Extension Of Product Shelf-life

Extension of Product Shelf-life for the Food Processor A strategic report compiled for the Food Processing Faraday by the Scientific and Technical Information Section, Leatherhead Food International.

Contents 1:

Page

Introduction

1

1.1:

Shelf Life

1

1.2:

Why Extend Shelf Life?

1

1.3:

Other Considerations

2

1.4:

Scope

2

1.5:

Benchmarking

3

2:

Extending Shelf Life? Safety Points to Consider

4

3:

Legislation

5

3.1:

Primary Legislation

5

3.2:

Secondary Legislation (Regulations)

5

4:

Conventional Technologies Extension of Shelf Life

6

4.1:

Introduction

6

4.2:

Hurdle Technology

6

4.3:

Heat Preservation

7

4.3.1:

Ohmic heating

8

4.3.2:

Microwave heating

8

4.3.3:

Other emerging heating technologies

4.4:

4.5:

5:

4.4.1:

Deep chilling

4.4.2:

Other emerging refrigeration technologies

Drying

9 10 10

4.5.1:

Microwave drying

11

4.5.2:

Heat pump drying

11

‘New’ Processing Technologies

13

High Pressure Processing

13

5.2:

Irradiation

15

5.3:

Natural Food Preservatives

17

5.3.1:

Natural antimicrobials

17

5.3.2:

Natural antioxidants

5.5:

7:

9 9

5.1:

5.4:

6:

Cooling

Other Developing Technologies

19 20

5.4.1:

Pulsed electric field

20

5.4.2:

Pulsed white light

20

5.4.3:

Ultra-violet light, pulsed ultra-violet light

21

5.4.4:

Ultrasound

21

5.4.5:

Combinations of preservation technologies with potential

22

Further Reading

22

Packaging

24

6.1:

Map

24

6.2:

Active Packaging

26

Decontamination Techniques

28

7.1:

Introduction

28

7.2:

Chemical Techniques

28

7.3:

8:

10:

11:

General considerations

28

7.2.2:

Water

28

7.2.3:

Ozone

29

7.2.4:

Chlorine (hypochlorite)

29

7.2.5:

Dimethyl dichloride

30

7.2.6:

Hydrogen peroxide

31

7.2.7:

Organic acids

31

7.2.8:

Peracetic (peroxyacetic) acid

32

7.2.9:

Other chemicals that may have a role as decontaminants

32

Thermal Techniques

34

7.3.1:

Hot water

34

7.3.2:

Steam

34

7.3.3:

Steam vacuum

35

7.4:

Other Technologies

35

7.5

Sources of Further Information

36

The Food Production Environment: Impact on Shelf Life

37

8.1:

Sourcing of Ingredients

37

8.2:

Storage of Ingredients

37

Processing Areas

37

8.3:

9:

7.2.1:

8.3.1:

Processing equipment

38

8.3.2:

Ventilation

38

8.4:

Clean Room Technology

38

8.5:

Cleaning Technology

39

8.5.1:

Traditional cleaning methods

39

8.5.2:

Clean in place (CIP) systems

40

8.5.3:

Novel cleaning methods

40

8.5.4:

Ultra-violet light

41

8.5.5:

Solid carbon dioxide (CO2)

41

Hygiene Monitoring - How efficient is cleaning?

43

9.1:

43

Visual Inspection

9.2:

Traditional Swab/Plate Methods

43

9.3:

Rapid Hygiene Monitoring

43

9.3.1:

ATP kits

43

9.3.2:

Colour hygiene tests

44

Estimating Shelf Life and the Use of Predictive Models

46

10.1:

Models Currently Available

46

10.1.1:

Combase

46

10.1.2:

Forecast

46

10.1.3:

Food Spoilage Predictor

46

10.1.4:

Seafood Spoilage Predictor

47

10.1.5:

ERH-CALC™

47

10.1.6:

Coolvan

47

10.1.7:

Water Analyzer Series

47

10.2:

Frozen Food Models

47

10.3:

Accelerated Shelf Life Testing

48

Sources of Further Information

49

1: Introduction This report was commissioned by the Food Processing Faraday in response to the identification of a need for information on the subject of shelf life extension among its members and other stakeholders. The Faraday also consulted with Regional Technology Transfer Centres (RTTCs) during the commissioning of the report. The RTTCs comments emphasised the need for the report to address the particular needs of small and medium enterprises (SMEs). The content and presentation of the report have been strongly influenced by these comments, and the result is aimed very much at smaller food processing operations.

1.1: Shelf Life The Institute of Food Science and Technology (IFST) defines the shelf life of a food as “The period of time under defined conditions of storage, after manufacture or packing, for which a food product will remain safe and be fit for use.” (It is important to note that this definition places safety before any other consideration) Every food product has a shelf life, because all foods deteriorate, albeit at very different rates and in different ways, and become unsafe or unpalatable. For example, fresh fish begins to deteriorate almost immediately, even at chill temperatures, due to the action of enzymes in the flesh and rapid microbial growth. On the other hand, fully sterilised canned foods may remain fit for consumption for several years.

•

Transfer of odours or flavours (e.g. tainting or flavour loss)

•

Changes caused by exposure to light (e.g. loss of colour)

•

Physical damage to packaging

These mechanisms are controlled by a number of factors, which may be product related (intrinsic), or environmental and process related (extrinsic). For example: Intrinsic factors: •

The composition and formulation of the

•

Product structure

•

Moisture content and water activity

•

pH and acidity

•

Level of oxygen and redox potential

product

Extrinsic factors: •

Storage temperature

•

Relative humidity

•

Exposure to light

•

Gaseous atmosphere

•

Processing

•

Hygiene

•

Packaging

Knowledge of how these factors, individually or in combination, affect the sensory, physical, chemical and microbiological characteristics of a food helps us to understand what limits its shelf life. But the same understanding also opens up the possibility to influence product shelf life by manipulating one or more factors. This is the basis of food preservation. In other words, the intrinsic and extrinsic factors above can be used by the food processor to extend the shelf life of products.

Examples of the mechanisms that limit shelf life include: •

Chemical or biochemical changes (e.g. browning, rancidity)

•

Microbiological growth and metabolism

•

Moisture migration into, or out of, the product

•

Gas transfer (e.g. ingress of oxygen)

1.2: Why Extend Shelf Life? There is clearly no point in investigating potentially expensive technical solutions for shelf life extension unless the end result represents a commercial advantage. In fact, in some cases, shelf life extension could be a positive disadvantage. For example, foods marketed as ‘fresh’ that have a shelf life of

1

three or four weeks may not be well received

now favoured and valued by consumers, and

by the consumer.

therefore by retailers. This means that many food processors will increasingly have to look

Some of the potential benefits of extending

to new technology and more sophisticated

shelf life are obvious, some less so. For

processing methods to maintain their position

example:

in the market.

•

Product can remain on sale on the shelf

1.4: Scope

•

Consumers favour products that

The aim of this report is to provide processors

‘keep well’

with practical information to help them to find

•

Fewer consumer complaints

appropriate technology that they can exploit to

•

More efficient production planning

gain all the benefits of extended shelf life.

•

Improved stock rotation

•

Reduced wastage and product returns

Some food preservation methods (e.g. drying

from retailers

and salting) have been in use for thousands of

More extensive product distribution is

years, and were probably developed to serve

possible

the then vital purpose of ensuring that food

Highly seasonal products can be

collected in times of plenty could still be

stockpiled

consumed when times were hard. Other

Most retailers require food deliveries

methods (e.g. canning and mechanical

to have at least 75% of shelf life

freezing) have been available for many

remaining

decades and hardly qualify as new technology.

for longer

• • •

•

New legislation (e.g. Animal ByProducts Regulations) identifies some

It is not the purpose of this report to provide

product that has exceeded its use-

an exhaustive review of all food preservation

by-date as ‘waste’ requiring

methods. The focus is on innovative new

expensive controlled disposal

technologies, or recent developments in existing (conventional) technologies,

Generally speaking, extension shelf life is more

particularly those that are, or may eventually

likely to be of benefit for highly perishable

be, of use to the smaller food processor. The

foods that are required to carry a ‘use by’

emphasis is on new practical developments

date. Many of those advantages listed above

that smaller companies may be able to use,

can be achieved with an increase in shelf life of

now or in the near future, to obtain real

just one or two days for some foods.

benefits in extended shelf life.

Nevertheless, more durable products that need only display a ‘best before date’ may also

Neither does this report go into great technical

benefit.

detail about the technologies described. The

1.3: Other Considerations

aim is to supply an overview in each case, to outline the potential applications, and to highlight the benefits and drawbacks of each

Some of the more traditional methods of

processing technology. Wherever possible, the

extending the shelf life of foods are becoming

interested reader is directed to sources of

increasingly unpopular. For example, many

further information throughout the report.

consumers do not want foods made safe and stable by the addition of high concentrations of salt or sugar, or by the use of chemical preservatives. The regulatory authorities too are beginning to look closely at the salt content of foods from a human health point of view. It is minimally processed foods that are

2

1.5: Benchmarking Before investigating the potential for extending product shelf life and the technology that might be used to achieve it, it can be a very worthwhile exercise to review the performance of a product to determine whether an extension will provide significant benefits. This exercise can also be used to define the baseline, from which the extent of those benefits can be measured. This can be done relatively easily by monitoring key indicators that are directly related to shelf life. •

Number of consumer complaints due

•

Quantity of product remaining unsold at

•

Extent of product failure in the

•

Typical shelf life of competitors

•

Degree to which shelf life influences

to product failure end of shelf life distribution and retail chain products production scheduling Carried out over a period of several months, this exercise should provide sufficient data to determine whether shelf life extension will provide benefits and to help quantify those benefits. The information collected will be vital for formulating a business case to extend shelf life.

3

2: Extending Shelf Life? Safety Points to Consider For many ambient stable and frozen food products shelf life is determined by a loss in quality leading to the product becoming unacceptable to the consumer. But in some cases, particularly for chilled foods, it can be the microbiological safety of the food that is the most important factor when determining shelf life. Food processors must be aware that when the shelf life of a product is extended, it is possible that the additional time on the shelf could allow food poisoning organisms to grow to dangerous levels This problem is most likely to occur in the chilled food sector. This is partly because many chilled foods undergo minimal processing that may not destroy microorganisms, but also because they are often vulnerable to contamination with food poisoning bacteria during production. However, microbiological safety issues are by no means limited to the chilled sector. For example, the development of long shelf life, ambient stored, modifiedatmosphere-packaged, part-baked bread products may produce an environment in which Clostridium botulinum (the organism that causes botulism) can multiply. This possibility has to be taken into account when such products are in development.

4

Some microorganisms can cause foodborne illness when present in very low numbers (e.g. Salmonella, and verocytotoxigenic Escherichia coli [a group that includes E. coli O157]), and these should be absent from all ready-to-eat products. There are other species, notably certain strains of Clostridium botulinum and Listeria monocytogenes, that may be present in chilled foods in low numbers, but which have been linked to severe foodborne illness when the conditions in the food are favourable for these organisms to increase in numbers. Both of these bacteria are able to grow, albeit slowly, at chilled temperatures. Extending the shelf life of chilled products could give enough time for dangerous levels to be reached. It is also possible that changes in processing could allow other hazards (chemical or physical) to be present in the finished product. It is vital that such possibilities are considered when an extended shelf life product is developed. The effect of the changes on product safety could be significant and so the HACCP plan for the product must be completely reviewed. Food processors must ensure that they have access to adequate expertise to do this effectively (e.g. a qualified food microbiologist). No extended shelf life product should be launched onto the market before the safety implications are fully understood and under control.

3: Legislation

Sources of further information

It is important to be aware of the framework

The Food Standards Agency

of food legislation that applies to many of the

http://www.foodstandards.gov.uk/

technologies included in this report. Although

enforcement/ foodlaw/

there are many possible methods of obtaining a longer shelf life for a specific food product,

Leatherhead Food International

the application of many of these is limited by

http://www.leatherheadfood.com/

law. Relevant food law is spread across a number of specific pieces of legislation, and

Campden and Chorleywood Food Research

these cannot be covered comprehensively in

Association

this report. The following represents a brief

http://www.campden.co.uk/services/

outline of the legislation that may apply, but it

legislation/ legislation.htm

is important to obtain expert advice wherever necessary.

EC Legislation http://europa.eu.int/index_en.htm

3.1: Primary Legislation The principal piece of primary legislation applying in the UK is the Food Safety Act 1990. Any extended shelf life product must first of all comply with the requirements of the Act in that it must not be ‘injurious to health’, and must be fit for human consumption. (Note: from 1/1/05, new EU legislation (Regulation (EC) No. 178/2002) will come into force that applies harmonised provisions for food safety requirements. These are essentially equivalent to the provisions already afforded by the UK’s Food Safety Act 1990.)

3.2: Secondary Legislation (Regulations) There are a number of food Regulations that may have an impact on the development of extended shelf life products. The Regulations covering the following areas may apply, and should be considered early in the development process. •

Composition

•

Novel Ingredients

•

Additives

•

Contaminants

•

Processing and Packaging

•

Labelling

•

Hygiene

5

4: Conventional Technologies Extension of Shelf Life

The following section deals with some recent

4.1: Introduction

commercial impact in the near future.

The shelf life of a wide range of foods has been successfully extended using ‘traditional methods’ for decades, and in some cases thousands of years. We can refer to these methods as ‘conventional technologies’, and they almost all fall into one of the following categories:

• • • •

Heat preservation Cooling Drying Chemical preservation

These four basic categories cover an enormous range of preserved food products that at first appear to be preserved by a similarly wide range of methods. However, almost all of these methods can be placed in to one of the above categories. For example: Heat preservation – pasteurisation, retorting and canning, aseptic processing, traditional cooking processes. Cooling – freezing and chilling. Drying – traditional drying (e.g. air drying), mechanical drying, baking, salting, conserving (e.g. jams). Chemical preservation – pickling, acidification, nitrite in meat curing, addition of sulphites, organic acids and esters. These technologies are very well established, and although continuously refined, have remained fundamentally unchanged for many years. These conventional technologies are not dealt with in detail here, but for more information on the traditional food preservation techniques you are referred to the ‘further reading’ list on page 50.

developments within those four conventional technologies that are predicted to make a

4.2: Hurdle Technology Modern consumers are moving away from heavily processed foods in favour of products that appear fresh and natural. This means that the market for foods preserved by traditional methods is changing, and sales of ‘minimally processed’ foods are growing steadily. Foods that utilise chemical preservatives, high salt or acid levels, and heavily heat processed foods, are under particular pressure from changing consumer preferences, and in some cases, from changes in the attitude of the regulatory authorities. Manufacturers therefore need to adapt to these changes by adopting less severe solutions, but this clearly means developing products that may have a seriously reduced shelf life. The safety of some foods can also be compromised (e.g. by reduction in salt or preservative concentrations). One solution to this problem is to use a number of different preservation technologies in combination to exploit the ‘hurdle effect’. Hurdle technology relies on the fact that preservation factors, such as heating, pH, water activity, redox potential, atmosphere, and chemical preservatives often have a synergistic effect in combination, and their effectiveness is therefore greater than would be expected by simply adding their respective effects together. The concept is applied mainly to microbiological spoilage of relatively short shelf life foods, and the idea is that the spoilage microbes may be able to overcome one or more factors (hurdles), but will not be able to ‘jump’ over all the hurdles present. For example, they may survive pasteurisation, and be able to grow at low moisture levels, but a small reduction in pH, or the addition of a preservative, may then be sufficient to inhibit their growth.

6

Examples of food products that apply hurdle

sterilisation processes on the other hand are

technology to extend shelf life:

designed to destroy all the microorganisms that would be able to grow in the finished

• • • • •

Cooked cured meat products

product under the conditions in which it is

Chilled fruit juices

stored and distributed. For some canned foods

Reduced sugar jams and spreads

that are intended for export to hot climates

Reduced fat spreads

this could mean applying a heat process

Mild flavour pickles and sauces

equivalent to 121 °C for 25-30 minutes at the slowest heating point in an individual pack.

An understanding of hurdle technology is

Whereas a thermisation process may be only

particularly useful in product design, and it can

65 °C for 15-20 seconds followed by rapid

be applied effectively by both large and small

cooling.

organisations. The essential questions that need to be asked at the product design stage

Recent developments in thermal processing

are:

have concentrated on minimising damage to the sensory characteristics of the product. This

What hurdles do I have in my product?

can be considerable, as is demonstrated by products such as sterilised milk retorted in

How high are they?

bottles, which now occupies a very small section of the market. For some products,

This is something that many food processors

prolonged heating at high temperature is not a

have in effect been doing for some time, but

problem. For example, some canned meats

without referring to it as hurdle technology. By

can be made using lower quality raw materials

describing the process in this way it becomes

because the severe heat process improves

much easier to apply to new products in a

palatability. However, more delicate products,

structured and formal way that can be

such as soups, sauces, dairy products and fruit

documented and reviewed.

juices can be badly affected by thermal processing.

Sources of more information The development of ultra high temperature Hurdle technologies: combination treatments

(UHT) and high temperature short time (HTST)

for food stability, safety and quality. Leistner,

processes in combination with aseptic filling

L. & Gould, G.W., New York. Kluwer

processes has helped to overcome these

Academic/Plenum Publishers, 2002.

problems.

4.3: Heat Preservation

UHT processes achieve commercial sterility by heating product (usually liquids) to very high

In essence, all heat preservation processes

temperatures (130-145 °C), and holding at

extend shelf life by the destruction of

that temperature for a very short time, often

microorganisms and/or by the deactivation of

for just a few seconds. The product is then

enzymes in fresh foods that could cause

cooled rapidly and filled into cartons, bottles,

spoilage.

pouches etc. in a sterile environment. This

The processes concerned range from very mild

means that the product remains at high

heat treatments (e.g. thermisation of raw milk)

temperature for the shortest possible time,

to very severe commercial sterilisation

thus minimising loss of quality, but maximising

processes applied to some canned foods.

the destruction of bacteria. The Tetra Pak

Thermisation and processes destroy a

system is one of the best examples of this

proportion of the heat sensitive

approach, but other systems are employed for

microorganisms in a product and increase the

a range of products.

time to spoilage, but a large proportion of the microflora may survive. Commercial

7

These systems lend themselves to liquid

Drawbacks

products, but are much more difficult to apply to foods containing solids, such as meat pieces or diced vegetables. Recent processing

• •

Capital cost of equipment Need to control product conductivity by

technology developments have focused on

formulation and pre-processing (e.g.

further improving in-container and aseptic

de-aeration.

systems for heat-processed foods, especially for products containing solid components.

Sources of further information

Some examples of such processing

APV ohmic heating.

technologies are as follows:

http://www.apv.com/HeatExchangers/ ohmicheating.htm

4.3.1: Ohmic heating Birmingham Uni presentation on Ohmic Ohmic heating generates heat by passing an

heating.

alternating electric current through a food that

http://web.bham.ac.uk/L.J.Davies/work/

has electrical resistance. Heat is generated

overview/sld001.htm

directly and there is no need to transfer heat into the food through a surface. The heating

Ohmic heating. Ruan R., Ye X., Chen P., Doona

rate is determined by the voltage applied and

C.J., Taub I. Thermal technologies in food

by the electrical conductivity of the product.

processing. Richardson P. Cambridge

The amount of heat that can be applied

Woodhead Publishing Ltd. 2001, 241-265.

depends on how much variation in conductivity exists in the product and by the residence

Preserving foods with electricity: ohmic

time.

heating. Rahman M.S. Handbook of food preservation.

Various applications for ohmic heating have

Rahman M.S. New York. Marcel Dekker, 1999,

been investigated, including continuous

521-532.

pasteurisation and sterilisation processes allied to aseptic filling. It has the potential to

4.3.2: Microwave heating

produce heat evenly through all the components in a product, even when quite

Microwaves are electromagnetic waves with a

large particulates are present. It therefore has

wavelength that can be measured in

a lot of potential for liquid foods containing

centimetres. They fit into the spectrum

solids, such as soups and sauces. Ready-meals

somewhere between infrared radiation and

and pasta are processed in this way in Japan,

radio waves. Microwaves generate heat by

but take-up in Europe is quite limited so far.

dielectric heating, which in simple terms involves the conversion of electrical energy

Advantages

into heat by making water molecules in the food oscillate rapidly in an electric field that

• • • •

Very energy efficient

changes direction. The molecules alternately

Reduced risk of fouling

absorb energy and then release it into the

Rapid heating (heating rates of up to 1 °C

food. The result is a rapid heating process that

per second)

can penetrate food quite effectively.

Easy process control Although microwave heating has been in use for many years in domestic and catering environments, the best established commercial use of microwave heating is the tempering of frozen meat to temperatures just below the freezing point to allow dicing or slicing prior to

8

further processing. Very large joints of meat

including blanching of vegetables, thawing and

can be tempered evenly in hours or even

pasteurisation of meat, drying applications and

minutes rather than days by conventional

post-baking of snack foods.

methods. Commercial pasteurisation processes have also been investigated.

4.4: Cooling

Advantages

The refrigeration of foods is a well established technology first developed over 100 years ago.

• •

Rapid and relatively even heating

Frozen foods have been commercially produced

Ease of process control

for about 80 years, and the chilled food sector has been expanding rapidly since the domestic

Drawbacks

refrigerator came into widespread use in the 1950s and 60s.

•

Capital cost of equipment Both chilling and freezing extend the shelf life

Sources of further information

of foods by slowing or completely preventing spoilage by microorganisms, and enzymic and

Industrial Microwave Systems

chemical reactions. However, there are

http://www.industrialmicrowave.com/

disadvantages with both processes.

FLAIR-FLOW II (F-FE 212/96): Microwave

For example, even at chill temperatures many

sterilisation, an AAIR project.

spoilage bacteria are still able to grow quite

http://www.flair-flow.com/industry-

rapidly (psychrotrophic bacteria), and these

docs/ffe21296.htm

may still cause spoilage and reduce shelf life significantly. The low temperatures in chilled

Handbook of microwave technology for food

food processing environments suit these

applications. Datta A.K., Anantheswaran R.C.

organisms well and they can colonise

New York Marcel Dekker, 2000.

processing equipment.

4.3.3: Other emerging heating technologies

Freezing processes can cause textural damage to foods when ice crystals form within cells in the food during freezing and damage their

Infrared (IR) heating

structure. Enzymic spoilage and oxidative rancidity are also able to proceed at

Radiation in the infrared part of the spectrum

temperatures well below freezing.

can be used to heat the surface layers of foods very rapidly and efficiently, and is used in

Refrigeration technology has been continuously

roasting, baking, or grilling processes. For

developed over the decades to improve the

example the baking of biscuits can be done

control, speed, cost effectiveness, and

more rapidly using an IR system.

application of both chilling and freezing processes. Recent developments have also

Radio frequency heating

focused on improvements in quality and extension of shelf life.

Radio frequency (RF) heating uses electromagnetic radiation at wavelengths

Some examples are as follows:

longer than those of microwaves and heats mainly by dielectric heating at lower

4.4.1: Deep chilling

temperatures, but increasingly by electrical conductivity heating as the temperature rises.

‘Deep chilling’ involves cooling a food to a

RF heating is rapid and even and has been

temperature just above its freezing point. Most

investigated for a number of applications,

foods freeze at temperatures below 0 °C, and

9

therefore deep chilling may achieve temperatures significantly lower than those

4.4.2: Other emerging refrigeration technologies

typically found in the chill chain, but without ice crystals being formed in the food. At these

Super freezing

temperatures, even psychrotrophic microorganisms grow only very slowly, or not

Super freezing refers to storage temperatures

at all. Therefore, the time for microbiological

in the range -40 to -60 °C, which is

spoilage to occur is greatly extended, as is

considerably lower than conventional freezing

shelf life. Furthermore, the growth of

(-20 to -30 °C). Storage at this temperature

psychrotrophic food poisoning organisms such

has been found to give significant

as Listeria is effectively prevented below 0 °C.

improvement in quality for some high value products, particularly oily fish such as tuna.

Deep chilling is used commercially to extend

Super freezing is used commercially in Japan

the storage life of some chilled foods, such as

for some fish products to achieve higher

ready meals and cooked meats. It is a very

quality, although the processing and storage

useful way of ensuring that large amounts of

costs are also correspondingly high. General

stock can be built up and stored before being

improvements in freezing technology may

released into the chill chain to meet fluctuating

allow the same approach to be applied to other

demand. The ‘cook chill’ system operates on

high value foods in the future.

the same principle. Dehydrofreezing Advantages Dehydrofreezing combines drying and freezing

•

•

Storage life can be extended significantly.

in a single process to produce improvements in

The life of some products may be

colour flavour and texture for some foods at

extended by several weeks.

low cost. The technique involves partially

The risk from the growth of

dehydrating the product to a moisture content

psychrotrophic food poisoning bacteria is

low enough (around 30% for vegetables) so

almost completely eliminated.

that it does not freeze when cooled to -20 °C. The method is used mainly for vegetables and

Drawbacks

fruits, and is said to give a higher quality product than conventional freezing.

• • •

Increased refrigeration and energy costs.

Rehydration times are also substantially less

Potential freshness and flavour loss during

than for conventional dried products. Energy

storage.

and transport cost benefits can also be

Very accurate temperature control is

achieved by dehydrofreezing, since the

required to avoid accidental freezing.

products weight is reduced, as is its volume. Dehydrofreezing differs from freeze-drying in

Sources of further information

that the product is not frozen under vacuum.

Food Refrigeration and Process Engineering

4.5: Drying

Research Centre http://www.frperc.bris.ac.uk/frperc.htm

Drying foods to preserve them is one of the oldest technologies in use in the food industry. Removing the moisture from a food product has the effect of reducing its water activity (the amount of water available in the product), and it is this that is the key factor in preservation. Once the water activity falls below about 0.6, no microbial growth is possible and so microbial spoilage does not

10

occur. Reduced water activity also inhibits

technologies, such as forced air convection or

chemical and enzymic spoilage. Many

vacuum drying, in practice.

conventionally dried products have a final water activity of 0.3 or less, and products such

Microwave drying has been applied to dried pet

as dried herbs and spices may have a shelf life

foods, fruit and vegetables, and is said to give

of a year or more, only limited by gradual

improvements in taste and texture and less

flavour loss.

shrinkage than conventional dryers.

Partial drying can also result in considerable

Advantages

increases in shelf life. For example, many dried fruits have a final water activity of between 0.6 and 0.85, achieved by removal of water and consequent concentration of sugars in the fruit. At this level, some moulds (xerophilic

• • • •

Improved sensory characteristics Potentially rapid heating and drying Reduced energy consumption Reduced running costs

moulds) are able to grow and cause spoilage. Fruits such as dried apricots need to be

Drawbacks

treated with quite large concentrations of sulphur dioxide, to prevent browning and microbial growth.

• •

Capital cost of equipment Possible product damage through the formation of ‘hotspots’ during drying

Drying technology has been continuously refined for many years, and a large number of

Sources of further information

conventional drying systems have been developed, including drum dryers, belt dryers,

Industrial Microwave Systems

spray dryers, and fluidised-bed dryers. The

http://www.industrialmicrowave.com/

principal aim of all drying systems is to remove moisture from the product rapidly and

Principles and applications of microwave

efficiently, minimising processing costs and

drying. Sanga E., Mujumdar A.S., Raghavan

loss of product quality. Different drying

G.S. Drying technology in agriculture and food

systems are best suited to particular products.

sciences. Mujumdar A.S. Enfield Science

For example, many dried dairy products are

Publishers, 2000, 253-289.

produced by spray drying, and diced vegetables are well suited to fluidised bed

4.5.2: Heat pump drying

drying. Heat pump dryers operate by cooling warm Two comparatively recent developments in

wet air drawn from the dryer over an

drying technology are:

evaporator coil, which cools the air to below its dew point. Water condenses on the coil and

4.5.1: Microwave drying

runs away. The dry cool air is then passed through a condenser, where it is re-heated

Microwave drying technology relies on the fact

before being passed through the dryer where it

that water molecules in food absorb energy

picks up more moisture from the product.

from microwaves and generate heat evenly

Conventional heat exchangers can be

throughout the product. This means that

combined with heat pumps to improve the

microwave dryers do not need to rely on

efficiency considerably.

heating by conduction and on the establishment of moisture gradients in the

Heat pump dryers are used widely for drying

food, both of which limit the efficiency of

wood, but have also been investigated for

conventional dryers. Nevertheless, microwave

drying pet foods, fish and fish products, and

drying is slow when used in isolation, and it is

confectionery.

usually combined with other drying

11

Advantages

•

Can operate at lower temperatures, or more rapidly than conventional dryers

• • •

Improved product quality Energy efficient Reduced processing costs

Drawbacks

• •

Capital cost of equipment Low drying temperatures may allow microbial growth during drying

•

Potentially difficult to clean

Sources of further information IEA Heat Pump Programme http://www.heatpumpcentre.org/

12

5: ‘New’ Processing Technologies

case of a ham for example, treatment is as effective at the centre of the mass of meat as it is near the surface.

Traditional thermal processes can be harsh and have an adverse effect on the sensory

•

all vegetative microbial cells and spores

properties and nutritional value of foods. In

may potentially be inactivated.

addition, many processors are seeking to minimise or avoid the use of conventional preservatives, such as sulphite, nitrite and

•

and manipulation of pH, to provide enhanced inactivation.

‘New’ processing technologies based on physical techniques for food preservation have

•

covalent bonds and HPP affects

processed foods with an extended shelf-life

hydrophobic and ionic bonds), HPP has a

that are additive-free and have not been

number of unexpected and interesting

subjected to extensive heat treatment. The

functional effects, particularly on proteins.

potential of a number of processing

These can be useful and desirable. For

technologies has been investigated - they

example,

include high-pressure processing,

• • •

electroporation, high-intensity laser and noncoherent light pulses, and high-strength magnetic field pulses.

commercially to any extent and, together with

High Pressure processing (HPP) is also known as high-hydrostatic pressure (HHP) or ultrahigh-pressure (UHP) processing. Pressures of around 300 to 700 MPa (3,000-7,000 times the pressure of the atmosphere) are applied to a food product for a short time, to achieve what has been described as ‘cold pasteurisation’. The process offers a number of advantages over conventional thermal food processes:

•

Inactivation of vegetative microorganisms can be achieved without detrimental effects on flavour, texture, colour and nutrient contents.

•

Pressure is transmitted uniformly through

Faster thawing of frozen foods. Modification of the surface active Induction of a cooked appearance to meat, fish and egg-white proteins.

the only ones that have been developed

5.1: High Pressure Processing

Enhanced digestibility of meat proteins.

properties of proteins.

•

High-pressure processing and irradiation are

are considered here.

Since the chemical effects of HPP are different from those of heat (heat disrupts

of the consumer and deliver high-quality

microwave and pulsed electric field processing,

HPP may be used in combination with other techniques, such as heat, irradiation

sorbate.

the potential to address some of the demands

If the applied pressure is sufficiently high,

•

HPP can be used for in-pack foods in flexible packaging, which eliminates the need for additional aseptic packaging processes.

Outline of the HPP process HPP processing can be applied to foods before or after packaging. The food is placed in a pressure-transmitting medium, such as water, oil, or alcohol contained in a vessel of sufficient strength to withstand the pressures applied during the process. Pressure is applied by means of a piston or a pump. Although the process is usually described as ‘cold’, the application of pressure does cause a very small increase in temperature. Generally there is no permanent change in the shape or appearance of the foodstuff. It undergoes about 15% compression, which is

a food product, which means that, in the

13

recovered when the pressure is removed,

microbial pressure resistance. The effects on

usually with little damage to the structure.

relevant enzyme systems must also be investigated.

Conventional batch processing systems were the first to become available. Batch systems

Applications

can handle both liquid and solid products, which must be pre-packaged. In-line systems

Fruits

can only be used for pumpable products such as juices.

HPP can enable the retention of the bright natural colours, textural properties and

The effects of HPP on shelf life

attractive taste of fresh fruits for an extended period. Careful process design has enabled

The chemical and microbiological effects of HPP

manufacturers to develop novel fruit products,

depend on a number of factors, the most

such as fruit pieces in clear juice gel and whole

important being process temperature and

berries in syrup.

treatment time. Bacteria vary in their pressure resistance. Generally, Gram-negative

One of the most well known commercial

vegetative bacteria are less resistant to

applications of HPP is the production of long-

pressure than vegetative Gram-positive cells.

life guacamole.

In particular, Staphylococcus aureus appears to have a high resistance to pressure. Bacterial

Meat

spores, particularly Clostridium spores, are most resistant to pressure. Combining

Although HPP offers the potential to inactivate

pressure with heat treatment, for example 90-

food poisoning bacteria such as Listeria,

110 °C and 500-700 MPa, has been shown to

Salmonella and Escherichia coli, the meat

inactivate spores of Clostridium botulinum in

industry has not yet invested in HPP to any

certain food systems. Pressure cycling

great extent. The process is likely to prove

treatments have also proved effective. HPP is

very costly. In addition, HPP affects the

most effective at inactivating bacterium at acid

sensory characteristics of raw meat, and also

pH values.

promotes protein denaturation. However, HPP has been successfully applied to ready-to-eat

Yeasts and moulds, which generally cause food

meats, such as cooked ham and salami.

spoilage rather than illness, have been shown to be inactivated by a few minutes of

Milk and dairy products

treatment at pressures of about 400 MPa. However, these treatments are not sufficient to

These react well to HPP treatment; however,

reduce levels of mycotoxins such as patulin.

from the point of view of cost, HPP is unlikely to be able to compete with heat treatments for

Research has shown that high pressure affects

the safe production of milk. However, since

different enzymes in different ways. Some

pressure can bring about changes in the

enzymes may be partially or completely

functional properties of milk proteins, interest

inactivated, whilst others may actually be

in HPP processing of dairy products continues,

stimulated. Enzymes associated with spoilage

particularly for cheese processing and the

can cause deterioration in appearance and

modification of the foaming, emulsifying and

taste, and unless these enzymes are

gelling properties of milk proteins.

inactivated, spoilage will occur. Shellfish To ensure the safety of food treated in this manner it is essential that the effectiveness of

In addition to inactivation of bacteria, oysters

HPP on microbial inactivation be studied in

and shellfish that have been subjected to HPP

detail, together with factors that affect

are extremely easy to shuck. Taste and

14

appearance are claimed to be unaffected. ‘Gold

Other companies include Engineered Pressure

Band Oysters’ are on sale in the US.

Systems International (Belgium and US), UHDE Hochdrucktechnik (Germany), Elmhurst

Ready meals/sandwiches

Research (US), Stansted Fluid Power (UK), Resato International (Netherlands), and

Also on sale in the US are high-quality fajita

Unipress (Poland).

kits, comprising high-pressure processed guacamole, salsa, fresh peppers and onions,

Sources of further information

and beef or chicken strips. Avure Technologies AB Avure Technologies AB suggests that HPP

www.avure.se

technology can contribute to savings for sandwich producers. The process can give a

European Federation of Food Science and

longer shelf life to fresh high-quality foods

Technology

without loss of organoleptic quality. The

www.EFFOST.org

Company says that its technology could extend the shelf life of fresh cooked meat fillings and

Research Groups working on HPP

wet fillings by a factor of between 2 and 4. The fillings are packed in a flexible pack, such

Food Quality Group, University of Strathclyde

as a pouch, and then processed. The packaged sandwich fillings can be kept in a cold store by

Basic Strategic Research at the Catholic

the producer and, unlike conventional

University of Leuven (Katholieke Universiteit

products, do not have to be used within a day

Leuven Netherlands)

or two of delivery. CSIRO Australia (orange juice) Advantages Teagasc (dairy products)

•

High quality product with good sensory properties

• •

5.2: Irradiation

Some desirable effects on food proteins Potential to develop and exploit new

In spite of a huge body of evidence to support

markets

its effectiveness, consumer resistance has discouraged the development of food

Drawbacks

applications of irradiation in Europe. However, irradiation is now permitted in more than 30

• • • •

High capital investment and operating

countries worldwide. In the US, since final

costs

approval for the irradiation of red meat was

Some bacterial spores and enzymes may

granted by the USDA in 2000, its use for

survive HPP processes

treatment of ground beef to combat

Long and complex development

Escherichia coli O157 H7 has increased very

procedures needed for new products

significantly. Irradiated meat products, such as

Currently a ‘niche market’ process

fresh and frozen hamburgers, are selling at premium prices in supermarkets across the

Manufacturers of HPP equipment

US.

Flow International Corp., ACB Pressure

Outline of the irradiation process

System-Alstom and Kobe Steel are the most important equipment producers at present.

Ionising radiation transfers energy to

These companies specialise in large industrial-

molecules, promoting the formation of ions or

scale systems for the food industry.

free radicals and causing a small percentage of chemical bonds to break. In microorganisms,

15

irradiation disrupts DNA and so causes the

boxes, whereas electron beams are only

destruction of microbial cells. The extent of the

suitable for treating individual shipping boxes.

effect depends on the applied radiation dose. Microorganisms vary in their susceptibility to

In the UK, there is just one licensed processing

irradiation; in addition, factors such as the

facility, which treats herbs and spices. There

food medium, influence the dose necessary for

are 12 licensed plants in Europe.

effective treatment. The following table gives an approximate guide to the radiation dose

Applications

level (in kiloGrays) required to achieve different effects.

Effects of Irradiation

Fruits and vegetables

Radiation Dose (kGy)

Inhibit sprouting of

0.1 – 3.0

0.5 – 1.0

senescence and reduce spoilage is permitted at levels of 2 kGy. As an example, irradiation at

1.0 - 10.0*

bacteria (pasteurisation

this level is effective at eliminating spoilage moulds and bacteria from fruits such as strawberries.

process) Destroy microbial spores

senescence is permitted at levels of 1 kGy. Similarly, irradiation of fruits to delay

destroy insect pests Destroy vegetative

as onions and potatoes. In the UK, irradiation of vegetables to delay

meat, fish Retard fruit senescence /

inhibiting sprouting of bulbs and tubers, such

0.05 – 0.25

potatoes, etc. Destroy parasites in

Irradiation is a well-established treatment for

10.0 – 50.0 kGy*

Herbs and spices

*At present, the WHO recommends a

Treatment of herbs and spices at 10 kGy to

maximum for food irradiation of 10 kGy.

control pathogenic microorganisms is the only application presently licensed in the UK.

Irradiation equipment

Meat

The radiation used for treatment can be

Radiation doses of up to 10 kGy have been

gamma, x-ray or electron beam: all provide

shown to be sufficient to destroy most

sources of energy that act in a similar way.

foodborne pathogens, including Salmonella,

Gamma-rays are produced using a system

Campylobacter, E. coli O157:H7, and Listeria

centred on a Cobalt 60 or Caesium 137 source.

monocytogenes. However, this is not sufficient

Electron beams and x-rays are generated using

to eliminate spores of Clostridium botulinum

a machine that can be switched on and off.

and some other species. Research has also

The electron beam system is the easiest to use

indicated that irradiation is not a suitable

on-line in a food factory. The equipment is

treatment for eliminating viruses from meat

more compact and requires less shielding. A

products. Irradiation is not able to inactivate

French plant, for example, has installed such a

prions in meat products and would not be

system for killing Salmonella in deboned

effective against the infective agent of BSE.

chicken meat. The SPI Circe II accelerator unit provides a dose of 5 kGy and is capable of

At present, poultry treated at 7 kGy for control

processing 3 tons/hour.

of pathogens is permitted in the UK.

Gamma- and x-rays, because they penetrate

As mentioned previously, irradiated ground

further into solid materials, can be used to

beef products are gaining widespread

treat palletised products in standard shipping

acceptance in the US.

16

Cereals

Further sources of information

Cereals irradiated at a dose of 1kGy to prevent

EC Commission on Food Irradiation

sprouting are currently permitted in the UK.

http://europa.eu.int/comm/food/fs/sfp/ fi_index_en.html

There is interest in the use of irradiation of bulk crops to replace chemical fumigants and

Food Standards Agency – research programme

ozone-depleting chemicals such as methyl

http://www.food.gov.uk/science/research/

bromide.

RadiologicalSafety/a05prog/a05projlist/

Advantages

Puridec Irradiation Technologies http://www.reviss.co.uk/puridec/

•

Powerful decontamination technique that

foodirradiation/foodirradiation.asp

can destroy microorganisms and insects

•

and retard germination and sprouting in

Isotron

seeds, fruits and vegetables.

http://www.isotron.com/home.htm

Has very little effect on sensory properties.

•

It can be used to treat packaged foods

5.3: Natural Food Preservatives

and foods in a frozen state.

• •

Irradiation treatment could enable the use

The use of natural alternatives to synthetic

of fumigation chemicals to be reduced.

antioxidants and preservatives has become of

Relatively low operating costs.

intense interest in the face of consumer concerns about food additives and product

Drawbacks

•

labels bearing multiple E numbers.

Irradiation could be used to

Natural preservatives may act to enhance shelf

decontaminate foods with high bacterial

life by different routes:

loads that would otherwise be unacceptable for sale.

•

•

If irradiation eliminates spoilage bacteria, but not pathogenic bacteria, there may be

spoilage or pathogenic bacteria

•

no visual indication that a food is unfit for consumption.

•

Microorganisms may develop resistance to

Antimicrobial activity – inhibition of Antifungal activity – inhibition of yeasts or moulds

•

Antioxidant activity – inhibition or retardation of lipid oxidation.

irradiation.

•

• •

Irradiation can cause detrimental effects

Natural preservatives may show one or more

on the nutritional value of certain foods.

of these different types of activity. They also

It may also have an undesirable effect on

exhibit a wide range of mechanisms of action,

texture.

which, in many cases are very complex.

High capital investment costs. Consumer concerns about the safety of

5.3.1: Natural antimicrobials

the process and irradiated foods. Antimicrobial agents prevent or inhibit the Manufacturers of irradiation equipment

growth of microorganisms. (Although this definition includes some traditional

IBA Food Safety Division, Memphis, Tenn.,

preservatives such as sugar, salt and vinegar,

produces cobalt-based irradiation services.

these are not considered here.)

SureBeam Corp., San Diego, Calif., offers electron beam equipment.

17

Antimicrobial enzymes

can destroy or inhibit the growth of other bacteria. Bacteriocins are isolated from foods

Lysozyme (E1105), which is derived from egg

that normally contain LAB, such as meat and

whites, is the most commercially important

dairy products, and as such, are already part

antimicrobial enzyme. At present, it is the only

of the human diet. Bacteriocins are the only

enzyme permitted as a preservative. Lysozyme

antimicrobial peptides currently used in the EU

is used against lactate-fermenting Clostridium

as food preservatives.

species in milk, and in ripened cheese to prevent ‘late blowing’.

Nisin is the most well known bacteriocin. Although nisin occurs naturally it is only

Other enzymes of natural origin with potential

considered to be a ‘natural’ preservative when

applications as antimicrobials are beta-

used in concentrations that do not exceed

glucanases and chitinases, which attack fungal

those that occur in foods fermented with a

cell walls, and oxidoreductases such as

nisin-producing culture.

lactoperoxidase, glucose oxidase and catalase, which catalyse reactions that produce cytotoxic

Bacteriocins are particularly suitable for use as

compounds. Glucose oxidase and catalase may

part of a hurdle strategy for food preservation,

also inhibit lipid oxidation and so act as natural

particularly in dairy products, meat and fish.

antioxidants.

They are generally effective against Gram positive bacterial cells and spores. Nisin has

Antimicrobial peptides

been shown to inhibit the development of Clostridium botulinum spores in cheese

A range of peptides displays antimicrobial

spreads and the growth of Listeria in soft

activity.

cheeses such as cottage cheese. Nisin is also used to control late blowing in matured

Peptides with iron-binding properties

cheese, and to inhibit the spores of spoilage bacteria in canned vegetables.

These peptides show an antimicrobial effect that is explained by their binding essential iron

Nisin has shown promise in certain meat

needed for microbial growth. Food poisoning

systems, but other bacteriocins, specifically

such as Listeria and Salmonella are reported to

pediocin, have proved more effective, for

be inhibited by antimicrobial peptides,

example against Listeria in chicken.

although in real food systems the effect has been found to be limited.

Antimicrobials from plants

Lactoferrin, which is present in the milk of

Essential oils

many species, is of particular interest. Its hydrolysate, known as lactoferricin, has a

Essential oils, obtained from plants by steam

much higher activity than native lactoferrin.

distillation, pressing or extraction, in addition

Lactoferrin has been shown to inhibit

to their characteristic aroma and flavour,

attachment of pathogenic bacteria to meat

usually contain phenolic compounds with a

surfaces. The USDA approved this use on beef

certain level of antimicrobial activity. Among

in January 2002.

the herbs and spices with oils best known for their antimicrobial properties are chilli, garlic,

Bacteriocins – antimicrobial proteins

sage, thyme, oregano and rosemary. The

produced by bacteria

activity of essential oils against microorganisms is strongly dependent on the

Lactic acid bacteria (LAB) produce a wide

food system in which they are used. It also

variety of different bacteriocins, which have

depends on other variables, for example, plant

potential applications as effective natural food

variety, climatic factors and extraction method.

preservatives. Bacteriocins are proteins that

18

Only a few essential oils have been shown to

the vegetables to form antimicrobial

have useful antimicrobial activity at

isothiocyanates. For example, sinigrin in

concentrations suitable for use in food

mustard seeds is cleaved by myrosinase to

processing; they include allspice, bay, basil,

give allyl isothiocyanate (AITC, the main

cinnamon, clove, garlic, lemon grass, mustard,

component of mustard essential oil). The

oregano, rosemary, sage and thyme. Among

gaseous form of AITC has been shown to have

the many food applications of essential oils as

greater antimicrobial activity than the liquid,

natural preservatives that have been

and at very low doses is effective against

investigated are the use of oregano oil against

spoilage fungi.

Escherichia coli O157:H7 in aubergine salads and basil oil for washing lettuces.

Phytoalexins

Essential oils are acceptable to the consumer

Antimicrobial phytoalexins are synthesised in

as natural preservatives. They have a long

certain plants in response to invasion by

tradition of use and are generally regarded as

microorganisms. They include pisatin from

safe (GRAS). However, their characteristic

garden pea, phaseollin from beans and rishitin

sensory properties limit their application to

from potatoes and tomatoes. It has been

foods that already have a strong flavour.

suggested that these might potentially play a role as natural food preservatives.

In addition to antimicrobial activity, essential oils often exhibit useful antioxidant activity.

5.3.2: Natural antioxidants

Rosemary, sage and oregano extracts are among the commercially available natural

Antioxidants are capable of retarding or

antioxidants and are used in several

preventing the development of lipid oxidation

commercial blends of natural products. Among

and may increase food product shelf life by

the suggested applications are meat, poultry,

inhibiting the development of rancidity. In

fish, oils, and soups.

addition, the majority of these antioxidants have a positive image to the consumer, and

Natural organic acids

are associated with a number of positive health effects, such as reduced risk of heart

Naturally occurring acids, such as acetic acid,

disease.

malic acid, citric acid, lactic acid and oxalic acid, work as antimicrobials mainly by lowering

Natural antioxidant compounds work by a

the pH of food. Applications are generally

number of different mechanisms, and

limited to products in which acid flavour is

antioxidant mixtures may prove to work

desired.

synergistically, or sometimes antagonistically. As may be expected, food components can

Enzyme-released antimicrobials

affect antioxidant activity, and so careful testing in the food system of interest is

Two main types of antimicrobial compounds

essential before any novel approach to

are activated by enzymes. The first group are

preservation is adopted.

found in plants of the Allium family (onion, leek, garlic). Of these, garlic gives rise to the

There has been considerable commercial

most potent antimicrobial, allicin. Research has

development in natural antioxidants in recent

shown that these substances inhibit most

years. Among the most important are

microorganisms, providing a high concentration

tocopherol/tocotrienol; ascorbic acid; herb and

is used.

spice extracts, such as rosemary, oregano and sage; green tea extracts; organic acids;

The second group are found in the Cruciferae

lecithin; carotenoids; and flavonoids. Many

(cabbage, mustard, horseradish). Hydrolytic

suppliers, including RC Treatt, Bush Boake

enzymes act upon the glucosinolate content of

Allen, Kalsec, ADM, Jan Dekker International,

19

Overseal, and Chr. Hansen now offer a wide range of different natural antioxidants or antioxidant blends. Many natural compounds have both

5.4: Other Developing Technologies 5.4.1: Pulsed electric field

antimicrobial and antioxidant activity. These

Microorganisms in foods may be inactivated by

include organic acids such as citric acid,

the application of very intense electric field

lactoferrin, and plant extracts.

pulses. The process, which takes only a few minutes, causes only a minimal increase in

Advantages

temperature, and no appreciable physical or chemical changes in the treated food.

•

A consumer-friendly label with no (or fewer) E-numbers.

In pulsed electric field (PEF) systems, energy supplied by a high-voltage power supply is

•

The replacement of chemical

stored in capacitors and discharged as short

preservatives and antioxidants, some of

pulses through a food material in a treatment

which may be associated with safety

chamber. At Ohio State University, one of the

concerns.

leading centres for the development of PEF technology, researchers have reported very

•

The concept of natural antioxidants is

positive results for extension of the high-

welcomed by the consumer. Natural

quality shelf life of liquids such as fresh orange

antioxidants are perceived as being

juice, skimmed milk, apple juice, liquid egg,

beneficial to health.

cheese sauce and salsa.

Drawbacks

At present no commercial PEF systems are in place. It has been estimated that the capital

•

To achieve equivalent activity to that of

cost for future commercial systems is around

chemical preservatives, higher doses of

twice that of commercial heat processing

natural preservatives are often required.

systems, and that, for fresh PEF-treated orange juice, the expected increase in price to

•

Certain natural preservatives may have a

the consumer would be about 3%.

strong characteristic flavour or odour, which may limit the dose that can be

Further sources of information

used. Ohio State University

•

The nature of the foodstuff substrate has

http://fst.osu.edu/pef/

a significant effect on the activity of

•

natural preservatives, which makes it

US Soldier Systems Center (Natick) Dual Use

particularly important to test the

Science & Technology (DUST) project

performance of the preservatives in the

http://www.seabeecook.com/rations/

real system.

new/new_dehy.htm

Higher costs than conventional

5.4.2: Pulsed white light

compounds.

Pulsed light treatment is the application of intense short flashes of broad-spectrum white light. It is able to inactivate microorganisms by a combination of photochemical means and light-induced photothermal effects. The ultraviolet content of the light provides the photochemical energy, and the high intensity

20

of the light pulses provides thermal energy,

doses may have potential applications as part

which, because the pulses are of extremely

of a combination preservation strategy.

short duration, is restricted to the extreme

According to researchers at Campden and

outer surface of the material to be treated.

Chorleywood Food Association, low-frequency, high-intensity ultrasound combined with heat

Pulsed light treatment is most effective on dry

treatment acts synergistically to enhance the

smooth surfaces, where there are no fissures

inactivation of spoilage and pathogenic

that could protect microorganisms from the

microorganisms by as much as twenty-fold.

light. Promising potential applications for extended shelf life include bakery products

Further information

such as bread, cakes, pizza and bagels. Online pasteurisation of drinking water and

FDA Center for Food Safety and Applied

sterilisation of packaging materials are among

Nutrition – the uses of ultrasound in the food

the applications closest to commercial

industry

introduction.

http://vm.cfsan.fda.gov/~comm/iftus.html

5.4.3: Ultra-violet light, pulsed ultra-violet light Light in the UV-C region (wavelengths

5.4.5: Combinations of preservation technologies with potential

200-80 nm) produces the strongest antimicrobial effect. It requires a much longer

It has been stressed throughout that when

treatment time than pulsed light, and, since

considering the implementation of novel

penetration levels are low, it is only suitable

processing or preservation measures for foods

for surface treatment. Since UV may produce

it is necessary to carry out careful testing, not

off-flavours in foods, the most promising

only to ensure food safety, but also to evaluate

applications are in treatment of packaging

the effects on food quality. In many cases the

materials. UV-C is currently in commercial use

use of a combination of preservation

for disinfecting air particle filters and

technologies increases the effectiveness of

decontamination of processing surfaces.

microbial inactivation without a quality penalty. Many different combination treatments have

5.4.4: Ultrasound

been investigated or proposed, some examples are listed below.

Ultrasound treatment involves the transmission of energy at frequencies higher than 18MHz.

Ultrasound causes microbial inactivation by

At present, ultrasound is used in food

cellular cavitation, and the effectiveness is

processing for a number of applications that

increased when used together with high

are not related to food preservation, such as

temperature or with high temperature and

degassing and foam control, mixing,

pressure. The combination treatments produce

emulsification and meat tenderisation. At high

a particularly marked increase in the

intensities, ultrasound has a lethal effect on

effectiveness of ultrasound at inactivating

microorganisms, and so has potential as a food

enzymes. For example, in milk, ultrasound and

preservation treatment.

heat act synergistically in the inactivation of alkaline phosphatase, lactoperoxidase and

One of the limitations of the use of ultrasound

glutamyltranspeptidase. Similarly, heat,

for preservation of foods is that the intensity of

pressure and ultrasound act synergistically in

ultrasound required to achieve microbial

the inactivation of lipase.

inactivation is such that can also have physical effects on foodstuffs. Ultrasound produces cell

High-pressure processing is effective against

cavitation, localised heating and can lead to

microorganisms, but less so against bacterial

the formation of free radicals. However, low

spores. Combining high pressures with heat

21

treatment has proved effective in certain food

introduction’ published by Campden and

systems such as tomato and other vegetable

Chorleywood Food Research Association Group.

products. Novak J.S., Sapers G.M., Juneja V.K. (2003) Pulsed electric field treatment is most effective

‘Microbial safety of minimally processed foods’

for foods of low pH. Fruit juices are good

published by CRC Press.

candidates for PEF treatment. PEF also has a synergistic effect when combined with

Ohlsson T., Bengtsson N. (2002) ‘Minimal

moderately elevated temperatures (50-60 °C),

processing technologies in the food industry’

and this has been investigated for skimmed

published by Woodhead Publishing Ltd.

milk. Rodriguez J.J., Barbosa-Canovas G.V., Natural preservatives are best used in

Gutierrez-Lopez G.F., Dorantes-Alvarez L.,

combination as part of a hurdle strategy. To

Yeom H.W., Zhang Q.H. (2003) ‘An update on

achieve the best results at the lowest dose

some key alternative food processing

levels additional techniques such as modified

technologies: microwave, pulsed electric field,

atmosphere packaging, heat treatment, and

high hydrostatic pressure, irradiation, and

pH modification have been suggested. Specific

ultrasound’ in ‘Food science and food

examples include modified atmosphere

biotechnology’ by Gutierrez-Lopez G.F.,

packaging with oregano essential oil vapour;

Barbosa-Canovas G.V., published by CRC

lysozyme and nisin with pulsed high-pressure

Press.

treatment; and pulsed electric field, nisin and carvacrol.

Stewart C.M., Cole M.B. (2001) ‘Preservation by the application of nonthermal processing’ in

Irradiation can act synergistically with heat

‘Spoilage of processed foods: causes and

treatment - the combination is more effective

diagnosis’ by Australian Institute of Food

at destroying viruses in meat products, for

Science and Technology Incorporated Food

example. Chilled storage and modified

Microbiology Group, Moir C.J., published by

atmosphere packaging also work well in

AIFST Inc.

combination with irradiation for meat and poultry products.

High-pressure processing

5.5: Further Reading

Anon (2003) ‘Keeping the pressure up’ Sandwich and Snack News Magazine (May) 18-19.

General Hendrickx M.E.G., Knorr D. (2002) ‘Ultra-highAnon (2003) ‘Effect of preservation

pressure treatment of foods’ published by

technologies on microbial inactivation in foods’

Kluwer Academic/Plenum Publishers.

Comprehensive Reviews in Food Science and Food Safety, Vol 2 (Supplement), 42-45

Raso J., Barbosa-Canovas G.V. (2003)

http://www.ift.org/cms/?pid=1000633.

‘Nonthermal preservation of foods using combined processing techniques’ Critical

Barbosa-Canovas G.V. (2002) ‘Key goals of

Reviews in Food Science and Nutrition, 43 (3),

emerging technologies for inactivating bacteria’

265-285.

Food Safety Magazine, August/September, 3442.

San Martin M.F., Barbosa-Canovas G.V., Swanson B.G. (2002) ‘Food processing by high

Clark J.P. (2002) ‘Thermal and nonthermal

hydrostatic pressure’ Critical Reviews in Food

processing’, Food Technology, 56 (12) 63-64.

Science and Nutrition, 42 (6), 627-645.

Leadley C., Williams A., Jones L. (2003) ‘New technologies in food preservation: an

22

Irradiation Deeley C. (2002) ‘Food irradiation – setting new standards or a slippery slope?’ Food Science and Technology, 16 (2), 52-55. Mendonca A.F. (2002) ‘Inactivation by irradiation’ in ‘Control of foodborne microorganisms’ by Juneja V.K., Sofos J.N., published by Marcel Dekker. Microwave processing Bengtsson N. (2001) ‘Development of industrial microwave heating of foods in Europe over the past 30 years’ Journal of Microwave Power and Electromagnetic Energy, 36 (4), 227-240. Doores S., (2002) ‘Microwave inactivation of pathogens’ in ‘Control of foodborne microorganisms’ by Juneja V.K., Sofos J.N., published by Marcel Dekker. Natural preservatives Cleveland J., Montville T.J., Nes I.F., Chikindas M.L. (2001) ‘Bacteriocins: safe, natural antimicrobials for food preservation’ International Journal of Food Microbiology, (December 4), 71 (1), 1-20. Roller S. (2003) ‘Natural antimicrobials for the minimal processing of food’ published by Woodhead Publishing Ltd. Thompkinson D.K., Singh A.K. (2000) ‘Natural food preservation systems’ Indian Food Industry, (September/October), 19 (5), 330-338.

23

6: Packaging Food packaging performs a number of important functions. Apart from protecting the food product from its environment and enabling easy distribution of delicate or difficult to handle products such as eggs or fresh produce, it also has to carry product information and has a marketing function. It also has to be convenient for the consumer to use, suitable for safe food contact, and cost effective. Packaging has had a key role in the maintenance and extension of food shelf life for many years, and in some cases it has an integral role in the preservation system. For example:

• •

Maintaining sterility of canned foods Maintaining sterility of aseptically filled drinks

• •

Exclusion of moisture from dried foods Long-term physical protection of frozen foods

•

Exclusion of light from vulnerable products (e.g. oils and fats)

• •

of new applications and possibilities for packaging as a major technique for controlling shelf life. The potential of such developments as oxygen absorbers, carbon dioxide absorbers, antimicrobial release films, and antioxidant release films is beginning to command considerable attention.

6.1: Map For most foods there is an ideal atmosphere that will optimise the shelf life of the product. This is true even for quite complex combination products. The purpose of modified atmosphere packaging is to provide an initial atmosphere in the pack that comes as close as possible to that ideal. For example, fresh cut produce continues to respire after packing and will rapidly use up the oxygen in the headspace of the pack, while levels of carbon dioxide increase. This promotes spoilage and reduces product shelf life. By supplying a higher initial level of oxygen in the pack, this can be overcome to some extent. Most MAP applications use a combination of three gases to produce an ideal atmosphere.

Oxygen barrier Microbiological barrier

•

Allows respiration to continue in fresh produce.

All of these are important, but they are

Prevents loss of initial colour (e.g. in red

essentially passive functions. In recent years

meats).

there has been rapid development of new

Inhibits anaerobic bacterial growth.

packaging techniques to produce systems that have a more active role in the preservation of food products.

•

gas mixtures. 20-100% in headspace inhibits some

atmosphere packaging (MAP), which has grown

bacterial and mould growth.

enormously over the last 20 years and now has a significant presence in a number of poultry, dairy products, chilled ready-meals, bakery products and seafood. The technology has developed from simple gas flushing designed to reduce oxygen levels in the pack, to sophisticated gas mixtures capable of producing significant extension of shelf life. More recently, other developments in the field of ‘active packaging’ have opened up a range

24

Carbon dioxide: The most important component in MAP

The best example of this is modified

sectors, including fresh produce, meat and

Oxygen:

•

Nitrogen: Inert gas used to displace oxygen and delay oxidation. Also indirectly inhibits aerobic microbial growth. Prevents pack collapse in high moisture and high fat foods that absorb carbon dioxide.

Other gases have also been investigated for

Product

possible application in MAP. These include

%

% Carbon

%

Oxygen

dioxide

Nitrogen

60-85

15-40

-

-

25

75

carbon monoxide, argon, nitrogen dioxide, and ozone. Of these, argon is the most promising

Red meat

from a commercial point of view. This inert gas

Poultry

fills the same functions as nitrogen, but is

White fish

30

40

30

-

60

40

Oily fish

more effective because of its higher molecular weight. Gas supplies

Hard cheese

-

100

-

Bread

-

60-70

30-40

Fresh pasta

-

-

100

Dried foods

-

-

100

Gases for MAP are most commonly supplied in pressurised cylinders, but liquid gases are also

Other food products for which MAP can extend

available, as are air separation systems for gas

shelf life include: ready meals; dairy products;

generation on site.

ground coffee; sandwiches; snack foods (e.g. crisps and nuts); dressed salads (e.g.

Packaging materials

coleslaw); cakes; and pastries.

The optimum gas mixture must be combined

Advantages

with a packaging material and pack sealing mechanism that allows the atmosphere in the

•

General benefits of a shelf life extension

pack to remain optimum as long as possible.

ranging from several days to several

For example, the packaging material must

months (i.e. less waste, wider

have sufficient barrier properties to prevent

distribution, improved production

gases diffusing out of, or into, the pack too

scheduling etc.).

quickly (This is a particular problem with carbon dioxide, which diffuses through plastic

• •

films more readily than other MAP gases.) But it must also be capable of forming a gas-tight

Improved hygiene from hermetically sealed packs.

•

seal. For this reason, a variety of laminates are used for MAP products, and it is important to

Improved product visibility.

Reduces the need for chemical preservatives.

•

ensure that the material used is matched to

Allows better separation of sliced products.

the gas mixture. Examples of laminates used include: nylon/PE; nylon/PVdC/PE; and

Drawbacks

nylon/EVOH/PE.

• It is also important to ensure that the ‘head

Increased costs:

•

space-to-product’ ratio is correct. If the

equipment

headspace volume in the pack is too large,

• • •

then the pack appears to the consumer to be poor value. If the headspace volume is too small the amount of gas mixture in the pack

Gas supplies Packaging material Analytical equipment to monitor gas mixtures

may be too low to have the desired effect. Applications

Capital cost of gas packaging

• • •

Quality assurance costs

Increased pack volume. Potential microbiological safety hazards (e.g. possible growth of Clostridium

MAP can give useful shelf life extension across a wide range of products, and not only highly perishable foods, such as fresh produce. Some

botulinum in low oxygen packs.

•

Vulnerable to seal failures and punctures caused by physical damage.

examples are given below, together with commonly used gas mixtures.

25

Sources of further information

or bakery products, and delaying oxidation of oils and fats.

Air Products http://www.airproducts.com/products/

•

Ethylene scavengers –

equipment/foodfreezers/index.asp

Also used in sachets or packaging films to absorb ethylene gas produced by some

Air Liquide

ripening fruits and vegetables. Can be used to

http://www.airliquide.com/en/business/

delay ripening and softening of produce such

industry/food/applications/

as bananas, avocados and potatoes.

map_packaging.asp

•

Carbon dioxide emitters –

Society of Food Hygiene Technology paper on

Carbon dioxide diffuses through plastic

MAP safety

packaging films more readily than other gases.

http://www.sofht.co.uk/isfht/

Sachets containing CO2 emitters can be used to maintain the original level. Useful for

irish_97_atmosphere.htm

preventing microbial spoilage in meat, poultry, Campden guidelines (paper publication)

fish, cheese and some fruits.

http://www.campden.co.uk/publ/ pubfiles/ tm34.htm

•

Ethanol emitters –

Sachets that emit ethanol into the pack Cryovac packaging

headspace have been developed in Japan.

http://www.sealedair.com/eu/en/

They can be used to increase the mould-free

products/food/default.htm

shelf life of bakery products.

BOC MAP fact sheet

•

http://www.boc.com/markets/

Films containing antioxidants such as

appdetail.cfm?appdetailid= 30&market_

tocopherol, BHA, or BHT can be used to inhibit

bs_id=46

oxidation of oils and fats in dried and high fat

6.2: Active Packaging

Antioxidant release films –

foods.

•

Antimicrobial release films –

Active packaging can be defined as packaging

Films impregnated with a range of

that interacts with the internal environment of

antimicrobial compounds (e.g. organic acids,

the pack. Some of the technologies currently

spice extracts, lysozyme, and other enzymes)

being developed are designed to modify the

have been developed to inhibit the growth of

atmosphere within the pack throughout shelf

spoilage and harmful bacteria on the surface of

life by absorbing or releasing gases, so that

meat, poultry, fish, bakery products, cheese,

the optimum gas mixture of an MAP system is

and fresh produce.

retained for a longer period. In other cases, Flavouring emitters –

the packaging is designed to interact with the

•

product itself, perhaps by the slow release of

Flavour compounds can be incorporated into

antimicrobial compounds or antioxidants.

polymers to produce packaging materials that minimise flavour loss and mask taints and off

Examples

•

Oxygen scavengers –

odours in a wide range of products.

•

Temperature compensating films –

Used either in sachet form, incorporated into a

Temperature compensating films, such as

label, or into the packaging film itself, to

‘Intelimer’ film, have a chemical structure that

absorb oxygen in the pack. Applications

changes abruptly and reversibly at a specific

include inhibition of mould growth on cheese

temperature. This ‘switch temperature’ can be anywhere between 0 °C and 45 °C. Below this

26

temperature, the film is an effective gas barrier, but it becomes much more permeable above the switch temperature. This can be used to compensate for the increase in the respiration rate of fresh-cut produce at higher temperatures. Current status of active packaging A great deal of research into active packaging is currently being undertaken, especially in Japan and North America. So far, only oxygen scavengers have had any significant commercial impact, although both ethylene scavengers and ethanol emitters are also used. The impact in Europe has been very limited to date, partly because of the effect of EU legislation on food contact materials, but also because of fears of consumer resistance. However, the European Commission has proposed a change to the regulations to allow active packaging applications, and it seems likely that there will be a surge in uptake of these systems in the next few years. Sources of further information Food Science Australia fact sheet (Active packaging) http://www.dfst.csiro.au/actpac.htm EU funded Actipak project http://www.voeding.tno.nl/ ProductSheet.cfm?PNR=Actipak Intelimer film http://www.landecag.com/Intelimer.asp

27

7: Decontamination Techniques

7.2.1: General considerations There are a wide variety of chemical

7.1: Introduction

decontamination agents that can be used and it may be a sensible precaution to rotate

The decontamination of raw foodstuffs, such as

different agents within a plant over time. This

raw meats and fresh produce, can enhance

helps to prevent the build-up of a resistant

food safety as well as reduce the numbers of

population of microbes.

spoilage microorganisms, and can help to achieve a longer shelf life for a product.

Safety for employees using chemicals should

Decontamination techniques can also help in

be taken into consideration. More information

prolonging the shelf life of ‘processed’ products

can be found in a health and safety executive

(e.g. cooked prawns) by removing

(HSE) information sheet entitled ‘Controlling

microorganisms that have re-contaminated the

exposure to disinfectants in the food and drink

product during or after processing.

industries’ Food Information Sheet No 29. http://www.hse.gov.uk/pubns/fis29.pdf.

Decontamination techniques currently used or proposed for industry include the use of

7.2.2: Water

chemicals, thermal or physical treatments, and other ‘alternative’ technologies. A number of

The effective removal of dirt and other

treatments used together can result in a

particles from fresh food using water has been

greater reduction of microorganisms than a

used throughout history. Simple washing can

single treatment.

slightly reduce surface microbial populations but the efficacy of water as a decontamination

It is important to note that decontamination

agent can be improved by ensuring that

technologies cannot usually be relied upon to

potable water is used, raising the temperature

completely eliminate pathogens or spoilage

of the water (up to 80 °C has been

microorganisms from foods. The main

suggested), using different application

exception to this is irradiation. But

methods (e.g. spraying, high pressure

decontamination does provide a means of

spraying), using the wash in conjunction with

reducing the initial levels of microorganisms

mechanical means such as brushes, agitation,

and so extend shelf life.

and/or using multiple washing steps.

7.2: Chemical Techniques

Water can also be used as a final step following other chemical sanitising methods.

There has been great interest in chemical

Water, particularly delivered using high-

decontamination techniques in recent years,

pressure hoses, can be used in meat carcass

especially in the US following serious food

trimming and is usually followed by the

poisoning outbreaks linked to raw meat and

application of a vacuum to remove

fresh produce. Many chemicals have been

contaminants. For fresh produce processing

evaluated for this purpose, and some have

water should be kept at higher temperatures

been approved by the US authorities and are

than produce to prevent bacteria and other

in commercial US. There has been less interest

microbes being drawn into the interior of the

in the UK, and European legislation does not

food product by a temperature-generated

contain a list of compounds that can be used.

pressure differential.

Any chemical used as a decontaminant must obviously be safe when applied to food and

Applications

there must be no antimicrobial residues left on the product, otherwise it could be seen as an

To remove and loosen dirt and reduce

added preservative and not a processing aid.

microbial contamination on fresh produce and meat carcasses.

28

Advantages

• • •

Natural sanitizer

Advantages

•

Consumer-acceptable Inexpensive

in the water used for washing

• •

Disadvantages

• •

Limited effectiveness

Can be generated when needed and does not need storage facilities

Drawbacks

•

Hot water can affect the colour, texture and flavour of produce

•

Operating costs are low

Use of untreated water may cause cross contamination

•

No chemical residue on treated product or

The capital cost of the initial equipment is high

•

The strong oxidising properties of ozone

Physical cleaning used with water can

can cause physical injury, such as black

damage produce and may lead to the

spots in bananas, or colour changes in

removal of waxy cuticles that are natural

some products

barriers to microorganisms

•

Ozone can be corrosive to materials used in processing equipment

7.2.3: Ozone

•

Difficult to control and monitor when organic loads vary

Ozone is a gaseous form of oxygen which,

•

Ozone can be toxic to humans

when dissolved in water, has been shown to be a powerful disinfectant. Ozone gas can be

Further information

generated either by using UV bulbs or corona discharges in an oxygen-filled atmosphere.

http://www.waterwise.co.uk/

Ozone has a short half-life and readily breaks

http://www.ozonetech.com/

down to oxygen so food treated with ozone will

http://www.boc.com/news/article_

have no residues left over from processing.

detail. cfm?ID=633

Ozone can be used as a gas during the chilled

http://www.praxair.com/

storage of various foods to reduce microbial spoilage. The gas dissolves into the water

7.2.4: Chlorine (hypochlorite)

contained in the food being stored and so reduces the levels of microorganisms on the

Chlorine-based chemicals, particularly liquid

exposed surfaces of the product. Ozone can

chlorine and hypochlorites, are probably the

also be used to decontaminate bottled water

most widely used sanitisers for

and to treat water used to decontaminate

decontaminating fresh produce.

meat and fresh produce. Chlorine compounds are usually used at levels Applications

of 50–200 ppm free chlorine and with typical contact times of 1–2 minutes. Although

Bottled drinking water production,

chlorine is more effective in solution at acid pH

decontamination of animal carcasses, in wash

levels, in order to minimize the corrosion of

waters for fruits, salads and vegetables, to

processing equipment, chlorine-based

extend shelf life during storage of various

sanitisers are usually used at pH values

products including fruit and vegetables. Ozone

between 6.0 and 7.5. Processing water should

has recently been suggested for use to

be kept at least 10 °C higher than the produce

decontaminate ready-to-eat meat and poultry

being treated to prevent microbes being drawn

products.

into the internal parts of the product by a temperature-generated pressure differential. The type of produce, the amount of organic matter and numbers and types of microbes

29

present on produce all affect the effectiveness

produce washing. CCFRDA Guideline No 38

of chlorine decontamination.

(2002).’

Washing produce in chlorine-treated water

Suppliers of equipment and sanitising

reduces the chance for cross-contamination

chemicals

between different batches of product. It is

http://www.proton-group.co.uk/

usual to rinse washed produce in clean water after decontamination. Chlorine compounds

7.2.5: Dimethyl dichloride

can then be classified as processing aids and residual chlorine on the produce could not be

Dimethyl dichloride (DMDC) is an effective

claimed to extend shelf-life, which would mean

sterilising chemical treatment used to

declaration on the label.

inactivate microorganisms, including moulds and yeasts, in a wide variety of beverages.

Applications

DMDC is added to the beverage immediately prior to bottling and the chemical undergoes

Chlorine is used in wash waters and assists

complete hydrolysis within a few hours to

with decontaminating the surfaces of fresh

methanol and carbon dioxide. This breakdown

fruits, vegetables, salads and fresh herbs.

into naturally occurring components means its

Chlorine treatments have also been suggested

use is as a ‘cold sterilant’ agent and not as a

for the decontamination of seeds for sprouting.

persistent antimicrobial in the product. DMDC

However, the effective use of chlorine for

is more effective as a sterilant at ambient and

decontaminating meat carcasses is disputed,

higher temperatures; however, it breaks down

and it not now considered acceptable practice.

more rapidly at higher temperatures and commercial suppliers recommend its use at

Advantages

around 10 °C. The activity of DMDC is also affected by the pH and alcohol content of the

• • • •

Readily available

treated product (products containing higher

Inexpensive

alcohol levels and lower pH require less DMDC

Well proven in use

for effective treatment). At levels lower than

Effective and simple to monitor

200 mg/l its taste is undetectable in products.

Drawbacks

•

May leave a residual taste or taint on the

Commercially available a ‘Velcorin®’ Applications

product

•

•

Chlorine rapidly loses activity on contact

Alcoholic and non-alcoholic wines, sports

with organic matter or exposure to air,

drinks, ready-to-drink teas, juice based

light or metals

beverages and carbonated and non-carbonated

The formation of potentially hazardous

artificial drinks.

chlorinated organic compounds upon treatment of fruits and vegetables with

Advantages

chlorine is a concern

•

Potential health and safety hazards

•

It does not affect the colour, taste, or odour of the beverage at use levels

Further information

•

It can reduce or eliminate the need for chemical preservatives in beverages

Guidelines are available for the use of chlorine

•

to wash fresh produce.

when used as a sterilant

• Campden and Chorleywood Food Research Association. ‘The uses of chlorine in fresh

30

Does not require declaration on the label Additional equipment required can be incorporated into existing filling lines

•

Low energy costs

•

Can remove the need for hot-fill allowing

•

more packaging options Drawbacks

• • •

Not completely effective against all

It has little impact on waste water or the environment

Drawbacks

•

Effective concentrations of hydrogen

microorganisms

peroxide may cause undesirable colour

Capital outlay for additional equipment

and appearance changes in treated

fitted to filling lines

carcasses

The chemical is hazardous and requires special handling

•

Unacceptable colour changes are reported with some types of fruit and vegetables, particularly mushrooms, strawberries and

Further information http://www.protectedbybayer.com/mpp/

raspberries Further information

global/applications/food_beverages/ beverages/

http://www.sanosil.com/index.htm

7.2.6: Hydrogen peroxide

7.2.7: Organic acids

The antimicrobial properties of hydrogen

The antimicrobial efficacy of organic acids

peroxide have been known for many years and

depends on type of acid, its concentration and

preparations where hydrogen peroxide is the

type of application. Efficacy also depends on

active compound are marketed as

pH, temperature and other factors in the food

decontaminating solutions for the food

matrix. Organic acids such as lactic and acetic

industry. In some countries the maximum

acid are probably the most widely used

concentration for meat and poultry carcasses is

chemical decontaminants to reduce bacterial

100 ppm. Dipping, spraying or treatment with

contaminants on beef, lamb, pork and poultry

hydrogen peroxide vapour is reported as

carcasses. Such acids are used prior to the

effective for some fruit and vegetable

chilling of carcasses as they are most effective

products. Combination treatments particularly

when applied at temperatures between 50–55

using hydrogen peroxide with acetic acid are

°C. Organic acids can be used in combination

reported as very effective for reducing

with other decontamination techniques, such

foodborne pathogens on some types of fresh

as high pressure water sprays.

produce. Research has found that organic acids may Applications

also be of use in the decontamination of fresh produce, including herbs. Citric, acetic, lactic,

To decontaminate meat and poultry carcasses.

tartaric acid, and other organic acids, alone, or

Has been suggested as useful as an

in combination with each other, as well as

antimicrobial in dairy products and to reduce

other cleaning agents such as chlorine and

mould contamination in dried fruits. To

surfactants, are all possible decontamination

decontaminate fresh fruit and vegetables.

agents.

Advantages

Applications

• • •

Rapidly breaks down leaving no residues

Decontamination of meat carcasses.

It leaves no odour and does not effect the

Decontamination of fresh produce. To reduce

taste of treated foods

the microbial load on fish and prawns. As a

It is non-toxic at use concentrations and

wash for poultry carcasses. As an external

has a neutral pH

decontaminant for cheese.

31

Advantages

• • •

Organic acids naturally occur in many

To use in waters for decontamination of fresh-

foods

cut, further processed and post-harvest fruit

Regarded as natural and environmentally

and vegetables. Used in poultry spray rinsing

friendly by the consumer

and chill water, and in red meat carcass

Readily available and relatively low cost

sprays.

Drawbacks

• •

Applications

Can cause the discolouration of meat

Advantages

•

concentrations peracetic acid does not

Their use may cause the emergence of

have an impact on colour, odour or taste

acid-resistant pathogens with reduced

of product

microbial competition on the

•

decontaminated meat

•

It breaks down mainly to acetic acid and water and so it is compatible with waste

The disposal of acids in wastewater can be a problem

•

When used at recommended

surfaces and off-flavours

treatment systems

•

It is supplied premixed so there is less

The use of organic acid treatments can

risk to processing personnel. It is non-

accelerate equipment corrosion

corrosive at use concentrations.

More information

Drawbacks

http://www.aamp.com/beefcarcslaug.htm

•

Is more expensive than hypochlorites

http://www.purac.com/documents/ literature/ FreshMeatEN.pdf

Further information

http://www.biokill.com.hk/PRODUCTS/ citrox.htm

http://www.ecolab.com/Initiatives/foods

http://www.agritrus.com/uses.htm#1

afety/ FST/Tsunami.asp

Organic acids. Samelis J., Sofos J.N. Natural

7.2.9: Other chemicals that may have a role as decontaminants

antimicrobials for the minimal processing of foods. Roller S. Cambridge Woodhead Publishing Ltd, 2003, 98-132.

Chlorine dioxide

7.2.8: Peracetic (peroxyacetic) acid

Chlorine dioxide extremely effective at low concentrations, typically levels of 3 ppm and 1 ppm are used for whole produce, and peeled

Sanitisers containing peracetic acid have been

potatoes respectively. When compared with

reported to maintain their efficacy in reducing

chlorine and hypochlorites, chlorine dioxide is

microbial loads over a broader pH range and in

less affected by organic matter and its activity

a higher organic loading than hypochlorite.

is unaffected by pH. Chlorine dioxide can be

Research has shown that in combination with

used to wash fresh fruit, vegetables and

surfactants such decontaminates can be

salads, although its use on some fresh produce

effectively used to reduce pathogens on fresh

may be restricted by legislation. It has been

produce. The maximum concentration for use

used in water for meat carcass washing and

on meat and poultry carcasses in 220 ppm.

processing, and in the preparation of ice to store fresh fish.

Available commercially as ‘Tsunami®’ Chlorine dioxide is difficult to store and transport and is usually generated on-site. This

32

process is expensive and carries serious health

organoleptic qualities of the food, residual

and safety concerns.

levels of this chemical following treatment have been considered excessive for human

Further information

consumption and CPC has yet to be approved for food use.

http://www.chlorine-dioxide.com/food/ index.htm

Further information

http://www.purate.com/ http://www.clo2.co.uk/

http://www.safefoods.net/cecure/cecure.htm

Trisodium phosphate

Acidified sodium chlorite

A mixture of water and food grade trisodium

Acidified sodium chlorite is prepared by mixing

phosphate (usually at concentrations between

sodium chlorite and citric acid (or another food

8-12%) is used to clean and decontaminate

grade acid such as phosphoric acid,

poultry carcasses. It acts as a detergent,

hydrochloric acid, malic acid or sodium acid

washing off faecal contaminants and dirt. It

sulfate). It can be applied onto food surfaces

decontaminates by acting as a surfactant due

by spraying or dipping at levels of 500-1200

to its high pH (pH of TSP solution is around

ppm. The time between mixing and application

12-13), minimising the ability of bacteria to

is less than 5 minutes. Chlorine dioxide is

attach to surfaces. It is used by spraying or

produced during application, but levels do not

dipping for up to 15 seconds, and is followed

exceed 3 ppm. Although there is no post

by a rinse in clear water. Trisodium phosphate

treatment water rinse required for its use for

solutions can be recycled. It has simple feed

poultry, meat and meat products there is a

and application systems.

post treatment water rinse applied to fruit and vegetables. There is also a withholding time

Unfortunately, it has a limited effect on

until the treated fruit and vegetables can be

spoilage microflora, and can be corrosive to

processed (i.e. cut up).

plant and equipment over extended periods of use. There are also waste treatment and

Further information

health and safety concerns. http://www.sanova.com/toc.htm Further information Activated lactoferrin http://www.rhodia-phosphates.com/ brochures/ phosprods/page7.asp

Lactoferrin in a ‘natural’ antimicrobial, the activated product (in a form that has the

Cetylpyridinium chloride

greatest antimicrobial properties) available for use as a decontaminating agent is derived

Cetylpyridinium chloride (CPC) is a quaternary

from milk. It is effective as a decontaminating

ammonium compound that has antimicrobial

agent because it prevents bacteria from

properties against many microorganisms. It is

attaching to carcasses. It also acts as an

not currently approved for food processing in

antimicrobial, preventing the growth of any

the US. Its potential is for use as a spray or

remaining cells. It is applied by an electrostatic

dip treatment to decontaminate carcasses, and

application followed by a water rinse to

studies have investigated its efficacy at

remove detached cells. In the US, it is

reducing foodborne pathogens using

permitted for use at up to 2% of a water-

concentrations between 0.5 and 1%.

based antimicrobial spray.

Although it is non-corrosive to metal, is not a severe health hazard, and has no effect on the

33

Nisin

•

Perceived by the consumer as a natural treatment

Nisin is an antimicrobial that is produced by bacteria found in milk, and is perceived as a

Drawbacks

‘natural’ food preservative. There are variable reports on the efficacy of nisin as a

•

decontaminating agent for meat, as nisin’s activity is affected by numerous factors such

Uses large quantities of water when compared with chemical treatments

•

Achieving adequate temperatures on the

as salt, fat content, pH, curing agents, storage

surface of meat product can be difficult

temperature, modified atmospheres and the

due to heat loss when water travels from

presence of other preservatives. Typically

nozzle to carcass

commercial preparations are supplied at 2.5%

•

nisin. The activity of nisin against some bacteria can be enhanced when used with co-

products

•

agents such as organic acids, or with other technologies such as high hydrostatic pressure.

Hot water can generate condensate on Hot water can affect the colour, texture and flavour of products

•

Can be expensive in energy costs

The addition of nisin to products can enhance pasteurization treatments allowing less

7.3.2: Steam

product-damaging heat regimes to be used.

7.3 : Thermal Techniques

Commercial processes for meat carcasses using steam pasteurization reduce bacterial counts by applying pressurised steam for

7.3.1: Hot water

around 6 seconds to the surface of carcasses after a washing step. This is usually followed

Hot water is used as an immersion treatment

by another cool wash to reduce heat damage

to control insects and post-harvest plant

to the carcass. Research indicates that

pathogens on fresh produce and it may be of

pressurised steam gives equivalent reductions

use as a sanitiser for whole produce that is

in pathogen numbers as for knife trimming or

then further processed for fresh-cut products

steam vacuuming. Processes using steam

or unpasteurised juices.

sterilization for the decontamination of herbs, spices, seasonings and seeds have also been

Research has indicated that for meat carcasses

developed. Material is exposed to saturated

a hot-water spray followed by a cold wash may

steam for a short time (a high

be more effective than a hot spray alone. The

temperature/short time [HTST] process), and

efficacy of hot water sprays can be improved

the product is dried and cooled.

by delivering the water under high pressure. Effective water temperature for the

Applications

decontamination of meat carcasses should exceed 74 °C, and research using water at

To reduce microbial counts on meat carcasses.

temperatures above 80 °C report no adverse

To decontaminate dried herbs, spices,

quality affects on the product. Hot water spray

seasonings and seeds.

treatments are via washing cabinets. Advantages Applications

• Decontamination of meat carcasses.

compared with hot-water sprays

• Advantages

34

Leaves no chemical residues on produce

Bacterial reductions are achieved without the use of corrosive chemicals

• •

Has reduced energy costs and water use

If used correctly, there is no visual quality effect on the carcass

•

For dried products, the process is more

effective than knife trimming and may remove

acceptable to the consumer when

the need for a visual examination by an

compared with irradiation

inspector. Treatment has been used as three even passes at a rate of 1 second per pass.

Drawbacks Applications

•

If applied for longer than 6 seconds, can affect the colour of meat products

•

To clean and decontaminate carcasses.

The effect on meat colour can cause plant personnel to reduce the application time

Advantages

or temperature that may lead to an ineffective procedure

• •

•

•

Improves visual appearance and

Requires expensive capital investment in

decontaminates small areas on a carcass

equipment

using a single treatment

Not suitable for all spices because causes

•

May be more effective than knife

the loss of volatile flavour and aroma

trimming and reduce the need for visual

components

inspections

The process raises moisture levels in dried powders, possibly resulting in higher

Drawbacks

mould counts

•

Can only clean small areas on a carcass at once

Further information

•

Tends to be used when faecal

http://www.ventilex.net/Steam%20

contamination is evident so would not be

Sterilization.htm

applied to microbial contamination on

http://www.revtech.fr/siteeng/

visually clean ‘areas’

food_decont.htm

7.4 : Other Technologies

Effect of steam condensation, hot water or chlorinated hot water immersion on bacterial

Other processes have been proposed for the

numbers and quality of lamb carcasses.

decontamination of fresh produce or meat

James C., Thornton J.A., Ketteringham L.,

carcasses. These include irradiation,

James S.J. Journal of Food Engineering, 2000

hydrostatic pressure, electric fields, pulsed

(March), 43 (4), 219-225.

light, microwaves, ultrasound, UV treatments, oscillating magnetic fields and biocontrol

7.3.3: Steam vacuum

agents. However, research into the efficacy of these treatments is limited and is ongoing.

The application of steam or hot water with a

Irradiation is permitted to reduce microbial

suction or ‘vacuuming’ treatment is a process

loads for meat products in the US. However,

used in meat carcass decontamination that

the process is probably more suited to packed

combines the physical removal of faecal

products rather than carcasses, so that post-

contamination along with the sanitisation of

process contamination does not occur, thus

the carcass. Typically, the process uses a

ensuring a safer product. In the EU irradiation

vacuum wand that has a hot water (82-88 °C)

is permitted at the time of writing for the

spray inside. Steam is delivered by two

decontamination of dried aromatic herbs,

external spray nozzles that have two functions;

spices and vegetable seasonings, but the

to decontaminate the carcass as well as to

process must be declared on product labels.

sterilise the outside of the vacuum wand. The technique functions as a spot cleaner for carcasses. Research indicates that a commercial steam vacuum system is more

35

7.5 : Sources of Further Information Meat decontamination http://www.meatscience.org/pubs/ newsltr/attach/ncbafs1.pdf Reduction of microbial contaminants on carcasses. Castillo A., Hardin M.D., Acuff G.R., Dickson J.S. Control of foodborne microorganisms. Juneja V.K., Sofos J.N. New York. Marcel Dekker, 2002, 351-381. Fresh produce http://www.cfsan.fda.gov/~comm/ ift3-5.html http://www.pestlaw.com/x/international /WHO-19991100A.html

36

8: The Food Production Environment: Impact on Shelf Life The processing environment can affect the shelf life of many foods. The main way in which the environment influences shelf life is by increasing the microbiological loading of the product. For any product that is susceptible to microbiological spoilage, and which is neither sterilised in its final container, nor aseptically filled after sterilization, the number of microorganisms present at the point of production will be an important factor in keeping quality. Important gains in shelf life can be achieved simply by applying good hygiene practice throughout processing. A clean and contamination-free processing environment and well trained staff will help to minimize the levels of microbial contamination that are present on a food product as it passes into the distribution chain. Some specific measures that can be taken are detailed below.

8.1: Sourcing of Ingredients The microbiological quality of raw materials can also have a significant impact on the final shelf life of a product. A microbiological specification for each ingredient should be agreed with the supplier; this should set tight limits for contamination wherever possible, but must be realistic for the ingredient and account for the environment in which it is produced. There is no point in setting a target that is not achievable. It should also be remembered that processing water is an ingredient in many foods. This should always be of potable quality, and should be monitored regularly, especially where there are water storage tanks and extensive distribution pipework within a plant.

Further information Development and use of microbiological criteria for foods. Institute of Food Science and Technology London IFST 1999.

8.2: Storage of Ingredients The appropriate storage of raw ingredients can influence the final shelf life of a product. Temperature, humidity and light can all affect the quality, and perhaps the safety, of a raw ingredient. Storage areas should be well designed for easy cleaning and must be kept clean. They should be free from pests and a system for stock rotation should be implemented. Food processing premises should be designed and operated so that raw ingredients cannot cross-contaminate processed product. Cross-contamination can not only impact on the spoilage of a product but also can lead to food poisoning.

8.3: Processing Areas Careful attention to the design of a processing area can help in extending the shelf life of a product. Materials used in ceilings, walls and floors should be able to be easily cleaned and all areas should be accessible for cleaning. Further information CCFRA Guideline No 40 (2002). Guidelines for the design and construction of floors for food production areas (second edition) http://www.campden.co.uk/publ/ pubfiles/ g40.htm CCFRA Guideline No 41 (2003). Guidelines for the design and construction of walls, ceilings and services for food production areas (second edition) http://www.campden.co.uk/publ/ pubfiles/ g41.htm

37

8.3.1: Processing equipment Design of equipment is extremely important. Processing equipment that is easy to clean is essential, and potential contamination traps, such as dead areas in tanks, valves, or pipes that are difficult to reach should be avoided. Paying attention to ease of cleaning at the design or purchase stage will pay dividends in operation. Easy to clean equipment not only has inherent advantages, but also encourages staff to apply proper cleaning procedures. Further information CCFRA Guideline No 39 (2003). Guidelines for the hygienic design, construction and layout of processing factories http://www.campden.co.uk/publ/ pubfiles/ g39.htm

8.3.2: Ventilation The air supply to, and air flow in the processing environment can affect the microbiological quality of a final product, since many microbial contaminants can be airborne. The appropriate use of air filters to remove airborne particles and microorganisms from incoming air in processing areas can reduce spoilage and extend shelf life. Design and layout can also have a big effect on the flow of air. For example, the position of external and internal doors is very important. In high-care areas where microbial contamination can pose a major risk, air supply and air flow can have a significant impact on the safety and spoilage of high-risk products, particularly in extended shelf life chilled foods such as cheeses, pizzas and pastas, and those products not receiving an additional heat treatment prior to consumption. Further information CCFRA Guideline No 12 (1996). Guidelines on Air Quality Standards for the Food Industry http://www.campden.co.uk/publ/ pubfiles/ g12.htm

38

Best practice guidelines on airflows in highcare and high-risk areas (2001). Silsoe Research Institute. http://www.sri.bbsrc.ac.uk/ Controlling air quality in the food industry. Wray S. International Food Hygiene, 2003, 14 (1), 11-13.

8.4: Clean Room Technology Clean room technology supplies clean air drawn through high efficiency filters (HEPA filters) that can almost completely remove microorganisms and other particles to a physically separated area within the plant (the clean room). The flow of air is also controlled within the clean room, which is usually kept under positive pressure so that unfiltered air is unlikely to be drawn in through entrances and exits. The staff working in the area must be well trained and should be dressed in appropriate protective clothing. Cleaning procedures for the surfaces and equipment should be validated and implemented. The movement of staff and materials in and out of the room should be strictly controlled to prevent cross contamination. In this way, an environment that is almost microbiologically sterile can be maintained. Clean room technology can assist in achieving a longer shelf life for fresh products that have a stage in their production process where they are vulnerable to airborne contamination. It is a technology that prevents rather than treats the contamination. Incorporating clean rooms into a process can help achieve a longer shelf life by ensuring a low level of microbial contamination, if not sterility, and physically preventing cross-contamination from elsewhere in the processing facility. The technology can also keep a product free from allergens or genetically modified material and help with the avoidance of foreign objects, e.g. human hair. Applications Clean room technology is useful to products that are exposed to air during filling, during

the transfer from preparation line to the

environment generally at adequate intervals

packaging area or for component products that

can therefore have a big effect on shelf life.

are assembled into consumer-ready portion packages. Cheese, fresh pasta, and bakery products may all benefit from this technology,

8.5.1: Traditional cleaning methods

and it has also been used to assemble ready meals.

Traditional cleaning using simple physical methods (e.g. scrubbing), chemical detergents

Advantages

or disinfectants and/or heat can be very effective for reducing soil and microbial loads

•

•

Suitable for refrigerated products that are

in a food processing environment. Even quite

processed but contain little or no

complex processing equipment may sometimes

preservative

need to be stripped down, inspected, and

Can help extend shelf life for fresh

cleaned by hand if necessary.

products without impairing quality

•

Can allow alternative packaging options

Special care should be taken for the cleaning

because lower process

of high care areas and chilled food production

temperatures/filling options are available

lines. Cleaning options for processing areas

using this technology

dealing with dry goods are limited mainly to physical methods, since the introduction of

Drawbacks

water and water-based liquids to dry areas should not normally be permitted on a routine

• •

High Initial outlay and running costs

basis. For areas hard to access, such as

High level of staff training needed

overhead surfaces, disinfectants can be used in a fogging (as an aerosol) system.

Further information In all cases it is important to develop a Clean room technology and its benefit to the

documented schedule of cleaning procedures

food and beverage industry. Schicht, H.H. New

of proven effectiveness for staff to follow.

Food, 1 (1998), 2, 18-23. An enormous range of cleaning chemicals is Guidelines for clean room technology.

commercially available, and the choice of

Guideline No. 14. Dairy Practices Council.

chemicals can be difficult. It is important to

Guidelines for the dairy industry relating to

ensure that the detergents and sanitizers used

sanitation and milk quality, volume 1. Dairy

are appropriate for the product and plant.

Practices Council Keyport DPC 2001.

Recent developments such as cleaning foams

8.5: Cleaning Technology

may be useful alternatives to conventional cleaning chemicals. While cost is an issue, effectiveness is more important. The potential

Effective cleaning is of vital importance in

cost of poor cleaning to a business can be very

ensuring that food products do not become

large.

contaminated with microorganisms and/or physical soil that may reduce product quality

Applications

and shelf life. Although microbiological concerns are paramount, cleaning helps to

Can potentially be used to clean all areas of

prevent other problems. For example, the

food processing establishments.

presence on surfaces of small amounts of fat or oil that have already begun to go rancid can

Advantages

accelerate rancidity in further batches of product. Removing soil and microorganisms from all product contact surfaces and the

• •

Usually requires little capital outlay Effective if done thoroughly

39

Drawbacks

dismantle the system. The CIP system is finetuned so that surfaces are in contact with

• • •

Can leave a residue on equipment that

santiser/rinse solutions at the correct

can cause a taint in product

concentration, for the appropriate time and at

Health and safety issues

the correct temperature. CIP systems can be

Some cleaning chemicals can be corrosive

fully automated or manually operated.

to equipment Applications Further information CIP is widely used in the dairy industry, Health and safety during use of disinfectants:

particularly milk processing plants. It is also

http://www.hse.gov.uk/pubns/fis29.pdf

used in liquid soup and sauce processing, in the brewery industry, for beverages, margarine

On line review of food equipment and

manufacture and desserts (e.g. ice cream).

cleaning: http://www.hs.state.az.us/phs/oeh/fses

Advantages

/food_eq_cl_san.htm

•

Reduces the downtime involved in

Cleaning and disinfection. Holah J. Chilled

dismantling a system, cleaning and

foods: a comprehensive guide. Stringer M.,

reassembling

Dennis C. 2nd edition. Cambridge. Woodhead

•

Publishing Limited, 2000, 397-428.

Can help in increasing shelf life because cleaning can be done more frequently and effectively

Cleaning and disinfection. Royal Institute of

•

Public Health and Hygiene. A supervisor’s handbook of food hygiene and safety. Royal

fewer chemicals

•

Institute of Public Health and Hygiene, London RIPHH, 1995, 69-81.

Increased safety, exposing workers to Can reduce use of cleaning chemicals and water if set up correctly

•

Lower labour costs involved in cleaning a process line

CCFRA Guideline No 44 (2003). Guidelines for the hygienic design, selection and use of dry

Drawbacks

cleaning equipment. http://www.campden.co.uk/publ/ pubfiles/g44.htm

• •

High capital equipment cost Needs very careful monitoring and finetuning to ensure system is effective and

MAFF (1998) A practical guide to the

efficient

disinfection of food processing factories and equipment using fogging.

Further information

8.5.2: Clean in place (CIP) systems

http://www.seiberling4cip.com/

CIP lends itself to liquid or semi-liquid

8.5.3: Novel cleaning methods

evol&dev.htm

processing operations where the equipment system used is in almost continuous use. CIP

A number of novel alternative cleaning and

systems are usually a part of the initial design

sanitising techniques and materials have been

of equipment and they are built in to it as an

investigated. They include the following:

integral component. CIP relies upon the use of a series of detergents, rinses, sanitizers, etc., to flush and wash an enclosed processing plant (e.g. in a dairy) without the need to totally

40

Ozone

Applications

Research has indicated that ozone is effective

Can be used to reduce microbial numbers on

at killing microorganisms attached to surfaces

food contact surfaces and on packaging. It is

as well as within an aerosol. Ozone treated

also used to control contamination in process

water can be used to reduce microbial loads in

water. UV lights can also be used to control

clean-in-place systems and as an effective

mould growth on the surface of stored

treatment for surfaces within the food

ingredients such as syrups in bulk storage

processing environment, storage areas and

tanks.

transport vehicles. Advantages Applications

• Disinfecting agent suitable for use on most food contact surfaces within a food processing

The process leaves no residue so there is no risk of taint transfer to product

•

Can be fast and is easy to use

plant Drawbacks Advantages

•

Leaves no chemical residue on surfaces so

• •

production can begin soon after use without the worry of chemical taint or contamination occurring

• •

Capital cost to purchase equipment Some microorganisms (e.g. mould spores) have significant resistance to UV light

•

Cannot penetrate below a surface, organisms in cracks or pits are protected

Can be generated easily on site Effective sanitiser

Drawbacks

Further information http://www.hanovia.net/uv-applications/ default.htm

•

Capital outlay for generation equipment

http://www.lenntech.com/will1.htm

Further information

8.5.5: Solid carbon dioxide (CO2)

http://www.ozonetech.com/ozone.html

An alternative to conventional cleaning is

CCFRA R&D Report 109 (2000). The evaluation

cleaning with pellets of carbon dioxide. CO2 pellets are mixed with an air jet and directed

of ozone for airborne and surface disinfection.

against the surface to be cleaned under high pressure at about 20 bar. The method works

8.5.4: Ultra-violet light

because an abrasive action takes place as the CO2 hardens the layer of soil to be removed,

Ultra-violet (UV) light can be used to disinfect

which then cracks and starts to peel off. As the

surfaces. Lamps producing UV radiation at the

CO2 pellets sublimate they enlarge their

optimum wavelength to destroy

volume about 700 times. The action continues

microorganisms are positioned above the

because the cracks formed in the surface dirt

surfaces that require treatment. Exposure time

allows carbon dioxide pellets to get under and

depends on the energy produced by the lamps,

between the soil. The method is suitable for

the distance from lamp to surface, and on the

organic soil and for microorganisms.

nature of the surface to be treated.

41

Applications Useful in areas where heavy soiling occurs that is difficult to remove by conventional methods. Can be used in dry areas as no water is used in the process. Advantages

•

Does not have the environmental clean-up issues associated with cleaning chemicals.

Drawbacks

•

Still an emerging technology.

Further information http://www.icesonic.co.uk/App-FoodUK.pdf

42

9: Hygiene Monitoring – How efficient is the cleaning? Although the food-processing environment may appear clean, it is very important that the effectiveness of the cleaning regime is monitored with respect to both removing soil and to reducing microbial contamination. This

Applications Monitoring microbial and/or chemical contamination on food contact surfaces and in the general food processing environment. Can be used to test specifically for food poisoning organisms or spoilage bacteria. Advantages

is achieved by the implementation of routine monitoring, which can include:

• •

9.1: Visual Inspection A visual inspection for visible soil on surfaces, accessible parts of processing equipment and

debris, greasy surfaces and sometimes

indication of source Drawbacks

• •

•

Inexpensive Immediately identifies obvious problems

Drawbacks

•

Cannot detect microbiological contamination or non-visible cleaning agent residues

•

Cannot be used for internal parts of processing equipment

•

Subjective and non-quantitative

9.2: Traditional Swab/ Plate Methods Microbiological contamination, and cleaning fluid residues, can be checked using traditional sampling, swabbing and cultural/detection methods or agar contact plates. Wet/dry swabs or sponge swabs are used to sample contamination on surfaces at specific points in the plant according to a sample plan developed using a statistical approach. The swabs are then analysed in a laboratory.

Takes time (days) for results, meaning exposed to contamination

surfaces.

• •

Cost of laboratory analysis that days of production can have been

evidence that cleaning agents still remain on

Advantages

Can give a detailed breakdown between types of contamination, giving an

other parts of the premises can be included in an inspection regime. This will pick up gross

Swabs are inexpensive

Does not detect food debris on a surface

Further information CCFRA Guideline No 20 (1999) Effective Microbiological Sampling of Food Processing Environments.

9.3: Rapid Hygiene Monitoring The need for a quick result in determining the cleanliness of processing areas has lead to the development of a number of ‘kits’ that give an indication of the hygienic status of a surface.

9.3.1: ATP kits ATP kits detect a chemical (adenosine tri phosphate) found in all living cells, including microbes and most food materials. The system uses this chemical to produce visible light, the amount of which can be measured. The greater the amount of light or ‘bioluminescence’ produced, the more living material is present. Therefore, it can be used as an indirect means of quantifying the amount of soil on a surface, and standards can then be set for different processing areas. The test can be applied on site and results are available within minutes. ATP kits can also be

43

used to measure residue levels in cleaning

9.3.2: Colour hygiene tests

liquids such as rinse waters. Colour hygiene kits do not require any ATP kits were originally developed to measure

specialist equipment and are usually self-

numbers of microorganisms in food, especially

contained tests that rely upon a single, and

dairy products. However, it is difficult to

sometimes a series of colour changes, to

remove the large amounts of non-microbial

indicate the hygiene status of a surface. Some

ATP present in most foods, and so the method

kits have been developed to detect residual

was adapted to measure the total amount of

protein on a surface and rely upon this to

ATP in a sample, giving an overall measure of

determine the cleanliness of the surface. These

cleaning effectiveness.

kits detect proteins and amino acids and are suited to high-protein environments, such as

Applications

meat.

Rapid monitoring of food contact surfaces to

Other kits detect the presence of residual

measure cleaning effectiveness and to indicate

carbohydrates and phosphates, and have been

when cleaning is necessary.

developed for use where low-protein composite manufactured product residues may be

Advantages

present, such as fruit and vegetable processing environments. A recent development has been

• • • •

Very rapid

colour hygiene kits that detect a group of

Can be used on site by unskilled

compounds that are found in all living cells.

operators

These tests have a similar role to ATP tests,

Laboratory facilities not required

but with no need to use a luminometer, and

Quantitative results

they are claimed to be more sensitive than kits detecting protein residues.

Drawbacks Applications

• • •

Chemical residues (e.g. from cleaning chemicals) can affect the results

Single-use tests in processing environments

Does not differentiate between general

and food preparation areas to determine the

soiling and microorganisms

levels of food residues on surfaces.

Relatively high purchase and operating costs

Further information

Advantages

• •

http://www.aboatox.com/hygiene_ monitoring. html#atp http://www.biotrace.com/content. php?hID= 2&nhID=16&pID=10

Very rapid Can be used on site by unskilled operators

• • •

Laboratory facilities not required Requires no purchase of equipment Relatively low consumable costs

http://www.charm.com/pdf/charmIIpocketswab.pdf

Drawbacks

http://www.promega.com/ http://pb.merck.de/servlet/PB/menu/ 1108160/ index.html

• • •

Semi-quantitative tests Tend to be less sensitive than ATP tests Gives no indication of the microbial loading on the surface

44

Further information http://www.neogen.com/ http://www.charm.com/pdf/vericleen.pdf http://www.hygiena.net/ http://www.biotest.de/ http://service.merck.de/microbiology/ tedisdata/prods/4976-1_31200_0001.html Hygiene in food processing. Lelieveld H.L.M., Mostert M.A., Holah J., White B. Cambridge. Woodhead Publishing Ltd. GBP135, 2003. Introduction to hygiene in food processing. Hutton T. Chipping Campden CCFRA. 30.00 pounds, 2001, 64pp, En Key. Topics in Food Science and Technology No. 4. Hygiene management in food factories. Thomas P. Oxford. Chandos Publishing Ltd, 72.00 pounds, 2000. The food hygiene handbook. Sprenger R.A. 11th edition Doncaster. Highfield Publications, 1999.

45

10: Estimating Shelf Life and the Use of Predictive Models Establishing the shelf life of many food products can be an expensive and timeconsuming business. It is essentially a process of informed trial and error, and the only really effective way to establish shelf life is to keep the product under typical storage conditions until spoilage occurs. But there are techniques now available that can be used to save a significant amount of time and expense by helping to predict what the shelf life will be. Used correctly, these techniques can result in reduced product development times and costs, allowing the time to market to be cut considerably. Simple mathematical calculations have existed for many years to predict the stability of some products. For example, the ‘Preservation Index’ and ‘CIMSCEE’ models for acetic acid preserved products, such as pickles and acid sauces, respectively, and ‘mould-free shelf life determination’ for bakery products. These are still applicable today although their application can be limited and not necessarily relevant to new product formulations that exploit the use of preservatives and/or alternative ingredients. The advent of the personal computer allowed the development and broad application of complex equations or ‘mathematical models’ to predict shelf life, or factors affecting shelf life, such as water activity or temperature, for many food groups. In many cases, these models have been incorporated into software packages that display the results (i.e. predicted time for spoilage, time to safety hazard, final moisture content, etc.) in a simple display form. The use of mathematical models to predict the shelf life and characteristics of different product formulations should always be used with caution and as a guide only. A great deal of experience is needed to interpret the output of the models, and an appropriate expert (e.g. a microbiologist for microbial safety and spoilage) should always be consulted. Any

46

actions or changes to product formulations implemented as a result of the predictions must be validated by appropriate trials.

10.1: Models Currently Available 10.1.1: Combase The microbiological safety and likely spoilage of a range of food formulations can be predicted using the Internet-based, publicly and freely available database of food microbiology data known as ComBase. ComBase, contains accumulated data on the growth, survival and death of foodborne pathogens and spoilage organisms across a broad range of environments relating to foods. A collection of predictive models using the ComBase data, such as Microfit and Growth Predictor, is available to download from the Internet. Further information http://wyndmoor.arserrc.gov/combase/ http://www.ifr.ac.uk/combase/

10.1.2: Forecast Campden and Chorleywood Research Association (CCFRA) has developed a collection of bacterial spoilage models. Ongoing research is increasing the range of models available through Forecast, as well as considering the effects of fluctuating temperature, dynamic processing environments, modified atmospheres and new product types. Forecast is available as a charged-for service. Further information http://www.campden.co.uk/content.htm

10.1.3: Food Spoilage Predictor Developed by researchers in Australia, Food Spoilage Predictor can be used to predict the rate of microbial spoilage in a wide range of chilled, high-protein foods, such as meat, fish, poultry and dairy products. The system uses a

small data logger that is integrated with the

Further information

software containing the models. It can predict remaining shelf life at any time in the cold

http://www.frperc.bris.ac.uk/pub/

chain and can also calculate total shelf life. The

pub13.htm

system is available for purchase in the UK.

10.1.7: Water Analyzer Series 10.1.4: Seafood Spoilage Predictor The Water Analyzer Series of programs can be Seafood Spoilage Predictor can be used to

used to predict water activity of component

predict the shelf life of seafood stored either

products under a range of differing conditions.

under fluctuating temperatures or under

The programs include: predicting water activity

constant temperature conditions. It was

of a component mix; programs to determine a

developed by the Danish Institute for Fisheries

safe moisture content for a product to prevent

Research and is available free on the Internet.

mould or the amount of water that can safely be put in a product; the water activity of a

Further information

product at different ambient temperatures; the expected water activity of a product

http://www.dfu.min.dk/micro/ssp/

formulation and how this can be changed; models to determine the efficacy of packaging

10.1.5: ERH-CALC™

films in maintaining water activity of a product; models to determine the changes in

The ERH-CALC™ software package is

moisture and water activity of a product over

applicable for perishable bakery products.

time in a packaged product; and the

Users can input basic recipe formulations and

calculation of vitamin breakdown over time.

the software calculates the theoretical equilibrium relative humidity (ERH). From this

Each model is available to download from the

data, the model then predicts the mould-free

Internet free of charge for evaluation purposes

shelf life (MFSL) of the ambient stored product

for a limited period. After this time, it can be

(using a simple calculation for MFSL). The

purchased.

software is available for purchase. Further information Further information http://www.users.bigpond.com/ http://www.campden.co.uk/publ/ pubfiles/ erhcalc.htm

webbtech/wateran.html

10.2: Frozen Food Models

10.1.6: Coolvan Although frozen foods are not subject to the Developed by the Food Refrigeration and

same deterioration by microbiological action as

Process Engineering Research Centre, Bristol,

most chilled/ambient stored products, the

UK, Coolvan predicts the temperature of food

quality of frozen products does deteriorate

during a single/multi drop journey in a

during storage, and a point will be reached

refrigerated van. Knowing the changes of

where the product is no longer acceptable to

temperature in a food can help in predicting

the customer, denoting end of shelf life. Frozen

shelf life as well as enabling a producer to

foods can have flavour, textural or colour

ensure that a chilled food will be at the correct

changes due to enzymatic action, loss in

temperature when it reaches the retailer. The

nutrients (e.g. vitamin C) and physical changes

software is available for purchase.

such as moisture loss or ice formation. Many of these changes have been described in equations or 'mathematical models' to help predict shelf life.

47

For more information

Further information

http://www.fsci.umn.edu/Ted_Labuza/P

Accelerated shelf-life tests. Mizrahi S. The

DF_files/papers/Frozen%20Food%20Shel

stability and shelf-life of food. Kilcast D.,

f%20Life% 20.pdf

Subramaniam P. Cambridge Woodhead

10.3: Accelerated Shelf Life Testing Another method of determining the shelf life of a product quickly is accelerated shelf life testing (ASLT). This is particularly applicable to products where the anticipated shelf life is long, and where the practicality of storing samples for many months or even years would cause an unreasonable delay in the product coming to market. ASLT is a means of compressing the life of the product into a shorter time-span, usually by increasing the storage temperature. This means that the changes that occur in a product during its life are speeded up. The extent of these changes can then be used to estimate the shelf life at the true storage temperature. The results of ASLT need to be interpreted with care. For example, in most cases ASLT cannot be applied to the microbiological changes that occur in foods because microbes have specific temperature ranges in which they grow. Elevated temperatures can often prevent a microorganism from growing, or can permit the growth of microorganisms not relevant at the normal storage temperature of the product. There are other physical issues in foods relating to shelf life that are changed by raising the temperature, so that observations at the elevated temperature are not necessarily applicable at normal storage temperature. However, ASLT can be useful in very specific applications, such as: the determination of potential spoilage of canned foods in the tropics; for mould-free shelf life of bakery foods; spoilage of beer; to study bloom development on chocolate; to determine the stability of edible oil; and to study oil stability in situ in products, such as crisps, biscuits and margarines. Surprisingly, it is also possible to apply ASLT to some frozen foods.

48

Publishing Ltd. 2000, 107-128.

11: Sources of Further Information General reading Shelf life. Man D. Oxford Blackwell Science Ltd. GBP19.99, 2002, 113pp, En. Food Industry Briefing Series. Shelf-life evaluation of foods. Man C.M.D., Jones A.A. 2nd edition. Gaithersburg. Aspen Publishers, 2000. The stability and shelf-life of food. Kilcast D., Subramaniam P. Cambridge. Woodhead Publishing Ltd, 2000. Food shelf life stability: chemical, biochemical and microbiological changes. Eskin N.A.M., Robinson D.S. Boca Raton. CRC Press, 2000. Shelf life of foods - guidelines for its determination and prediction. Institute of Food Science and Technology. London. IFST, 1993. Internet Department of Environment, Food and Rural Affairs: http://www.defra.gov.uk/ Health Protection Agency: http://www.hpa.org.uk/ Hygiene advice from the UK Food Standards Agency: http://cleanup.food.gov.uk/ Institute of Food Science and Technology: http://www.ifst.org/ Royal Institute of Public Health and Hygiene: http://www.riphh.org.uk/ The Society of Food Hygiene and Technology. http://www.sofht.co.uk/ The UK Food Standards Agency: http://www.foodstandards.gov.uk/

Trade associations Biscuit, Cake, Chocolate and Confectionery Alliance (BCCCA), 37-41 Bedford Row, London WC1R 4JH. Tel +44 (0) 207 404 9111. Web site: http://www.bccca.org.uk/ British Sandwich Association. Picton House, Lower Church Street, Chepstow, Gloucestershire. NP16 5XT. Tel: +44 (0) 1235 821820. Web site: http://www.sandwich.org.uk/ British Retail Consortium. 21 Dartmouth Street, London, SW1H 9BP. Tel: +44 (0) 20 7854 8900 http://www.brc.org.uk/ Chilled Food Association (CFA). PO Box 6434, Kettering, NN15 5XT. Tel: +44 (0) 1536 515395. Web site: http://www.chilledfood.org/ Food and Drink Federation (FDF). 6 Catherine Street, London WC2B 5JJ. Tel: +44 (0) 207 836 2460. Web site: http://www.fdf.org.uk/home.aspx Fresh Produce Consortium (UK). Minerva House, Minerva Business Park, Lynch Wood, Peterborough, PE2 6AR. Tel: +44 (0) 1733 237117. Web site: http://www.freshproduce.org.uk/ Meat and Livestock Commission (MLC). Head Office, Meat and Livestock Commission, PO Box 44, Winterhill House, Snowdon Drive, Milton Keynes, MK6 1AX. Tel: +44 (0) 1908 677577. Web site: http://www.mlc.org.uk/ Soil Association, Bristol House, 40-56 Victoria Street, Bristol, BS1 6BY. Tel +44 (0) 117 929 0661. Web site: http://www.soilassociation.org/ Technology transfer centres The Department for Food and Rural Affairs (DEFRA) have funded Regional Food Technology Transfer Centre that act as a point of contact for small and medium-sized regional

49

food companies with food-related technical needs. Agrifood Centre (Newton Abbot): Tel: 01626 325858 http://www.agrifoodcentre.co.uk/sfdsn1. html CHARIS (Ayr): Tel: 01292 670166 http://www.hri.sari.ac.uk/flashframeset. html Food Technology Centre (Middlesbrough): Tel: 01642 499113 http://sst.tees.ac.uk/ftc/ Food Innovation Centre (Sheffield): Tel: 0114 2253976 http://www.shu.ac.uk/schools/slm/fic/ Food Knowledge and Know-How (Reading): Tel: 0118 9316520 http://www.fkk-reading.co.uk/ London Food Centre (London): Tel: 020 7815 7988 http://londonfood.org.uk/ North West Food Centre (Manchester) Tel: 0161 247 2493 http://www.nwfoodcentre.com/ East Midlands Food Technology Centre (Nottingham); Tel: 01636 817000 http://science.ntu.ac.uk/external/fhc/ organisation.htm Training courses Campden and Chorleywood Research Association http://www.campden.co.uk/ Chartered Institute of Environmental Health http://www.cieh.org/training/courses/ foodsafety/ Leatherhead Food International

Please note: Leatherhead Food International

http://www.lfra.co.uk/

uses every possible care in compiling, preparing and issuing the information herein given, but can accept no liability whatsoever in connection with it.

50

Food Processing Faraday Partnership Ltd

Leatherhead Food International

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