Lecture 10 Preservatives

Food Chemistry Lecture 10: Preservatives

Introduction 

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A preservative is a natural or synthetic chemical that is added to products such as foods, pharmaceuticals, paints, biological samples, wood, etc. to prevent decomposition by microbial growth or by undesirable chemical changes Why add preservatives to food?  

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To prevent lipid and fat oxidation – taste and smell bad and harmful for consumption To prevent molds & bacteria from growing.

Difference between food additives and food preservatives 

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Food Additives – any substances that becomes part of a food product when added through processing, storage or packaging Food Preservatives – any additives that extend a food's freshness or shelf life and keep it from spoiling or oxidizing

Type of Preservatives  

Preservative food additives can be used alone or in conjunction with other methods of food preservation Synthetic Preservatives 

Common anti-microbial preservatives include • • • •

Calcium propionate Sodium nitrate Sodium nitrite Sulphites (sulfur dioxide, sodium bisulfite, potassium hydrogen sulfite, etc.) • Disodium EDTA 

Antioxidants • BHA and BHT

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Other preservatives (non-food) • Formaldehyde • Glutaraldehyde • Methylchloroisothiazolinone

Type of Preservatives 

Natural Preservatives  Organic

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acid

Citric acid Benzoic acid Sorbic acid Propionic acid Acetic acid

 Vitamin

C  Tocopherols

Food Additives 

Acids   

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Acidity regulators 

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Anticaking agents keep powders such as milk powder from caking or sticking. Calcium carbonate, Magnesium Carbonate

Antifoaming agents 

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Acidity regulators are used to change or otherwise control the acidity and alkalinity of foods. Citric, acetic and lactic acids

Anticaking agents 

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Food acids are added to make flavors "sharper", and also act as  preservatives and antioxidants. vinegar, citric acid, tartaric acid,  malic acid, fumaric acid, lactic acid

Antifoaming agents reduce or prevent foaming in foods. Silicone derivatives

Antioxidants   

Antioxidants such as vitamin C act as preservatives by inhibiting  the effects of oxygen on food, and can be beneficial to health. 

Food Additives 

Bulking agents 

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Food coloring 

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In contrast to colorings, color retention agents are used to preserve a food's existing color: Ascorbic acid

Emulsifiers 

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Colorings are added to food to replace colors lost during preparation, or to make food look more attractive.

Color retention agents 

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Bulking agents such as starch are additives that increase the bulk of a food without affecting its nutritional value.

Emulsifiers allow water and oils to remain mixed together as in mayonnaise, ice cream, and homogenized milk: Lecithin

Flavors 

Flavors are additives that give food a particular taste or smell, and may be derived from natural ingredients or created artificially

Food Additives 

Humectants 

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Preservatives   

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Stabilizers, thickeners and gelling agents, like agar or pectin (used in jam for example) give foods a firmer texture. While they are not true emulsifiers, they help to stabilize emulsions

Sweeteners 

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Preservatives prevent or inhibit spoilage of food due to fungi,  bacteria and other microorganisms: Nitrites

Stabilizers 

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Humectants prevent foods from drying out: Glycerine

Sweeteners are added to foods for flavoring. Sweeteners other than sugar are added to keep the food energy (calories) low: Table sugar

Thickeners 

Thickeners are substances which, when added to the mixture, increase its viscosity without substantially modifying its other properties: Guar gum, xanthan gum

Calcium Propionate   

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Calcium propionate or calcium propanoate is the calcium salt of propionic acid As a food additive, it is listed as E number 282 in the Calcium propionate is used as a preservative in a wide variety of products, bread, other bakery goods, processed meat and other dairy products In agriculture, it is used, amongst other things, to prevent milk fever in cows and as a feed supplement Propionates prevent microbes from producing the energy they need, like benzoates do. However, unlike benzoates, propionates do not require an acidic environment.

Calcium Propionate  

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Calcium propionate is used in bakery products as a mold inhibitor Mold contamination is considered a serious problem amongst bakers, and conditions commonly found in baking present near-optimal conditions for mold growth A few decades ago, mold was a serious problem but today's improved sanitary practices in the bakery, have virtually eliminated this form of spoilage – Calcium propionate and sodium propionate are effective against mold According to the Pesticide Action Network North America, calcium propionate is slightly toxic Calcium propionate can be used as a pesticide

Sodium Nitrate  

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Sodium nitrate is the chemical compound with the formula NaNO3 This salt, also known as "Chile saltpeter" (to distinguish it from ordinary saltpeter, potassium nitrate), is a white solid which is very soluble in water Sodium nitrate is used as an ingredient in fertilizers, explosives as well as in glass and pottery enamels; the compound has been mined extensively for those purposes Sodium nitrate is also synthesized industrially by neutralizing nitric acid with soda ash Sodium nitrate has antimicrobial properties when used as a food preservative. It is found naturally in leafy green vegetables

Sodium Nitrite 

As a food additive, it serves a dual purpose in the food industry:  

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Enhance the color of preserved fish and meats Prevents growth of Clostridium botulinum, the bacteria which causes botulism

In the European Union it may be used only as a mixture with salt containing at most 0.6% sodium nitrite. It has the E number E250 While this chemical will prevent the growth of bacteria, it can be toxic for mammals. For this reason, sodium nitrite sold as a food additive is dyed bright pink to avoid mistaking it for something else Principal dangers of using sodium nitrite as a food additive is the formation of carcinogenic nitrosamines by the reaction of sodium nitrite with amino acids in the presence of heat in an acidic environment – cooked meats Recent studies have found a link between high processed meat consumption and colon cancer, possibly due to preservatives such as sodium nitrite

Sulfites 

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Sulfites are sometimes added to foods to act as enhancers or preservatives. They may come in various forms, such as:  Sulfur dioxide  Potassium bisulfite or potassium metabisulfite  Sodium bisulfite, sodium metabisulfite or sodium sulfite Some humans are allergic to sulfites. It is an undeclared allergen that may cause breathing difficulty within minutes after eating a food containing sulfites Asthmatics and people with allergies to aspirin (also known as salicylate sensitivity) are at an elevated risk for reaction to sulfites FDA prohibits the use of sulfites in foods that are important sources of thiamin (vitamin B1), such as enriched flour, because sulfites destroy the nutrient.

Sulfites 

Sulfur dioxide  Main

product from the combustion of sulfur compounds is often described as the "smell of burning sulfur" but is not responsible for the smell of rotten eggs  Sulfur dioxide is sometimes used as a preservative for dried apricots and other dried fruits due to its antimicrobial properties  The preservative is used to maintain the appearance of the fruit and prevent rotting. Its presence can give fruit a distinctive chemical taste

Sulfites 

Potassium bisulfite or potassium metabisulfite  A white crystalline powder with a pungent sulfur odour  The main use for the chemical is as an antioxidant or chemical sterilant.  Potassium metabisulfite is a common wine additive, where it forms sulfur dioxide gas (SO2)  This prevents most wild microorganisms from growing, and it acts as potent antioxidant, protecting both the color, and delicate flavors of wine

Sulfites 

Sodium bisulfite, sodium metabisulfite or sodium sulfite   

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Used in almost all commercial wines, to prevent oxidation and preserve flavor In fruit canning, sodium bisulfite is used to prevent browning (caused by oxidation) and to kill microbes In the case of wine making, Sodium bisulfite releases sulfur dioxide gas when added to water or products containing water. The sulfur dioxide kills yeasts, fungi, and bacteria in the grape juice before fermentation When the sulfur dioxide levels have subsided (about 24 hours), fresh yeast is added for fermentation. It is later added to bottled wine to prevent oxidation (which makes vinegar), and to protect the color of the wine from oxidation, which causes browning. The sulfur dioxide displaces oxygen in the bottle and dissolved in the wine.

Disodium EDTA    

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EDTA is a widely-used abbreviation for the chemical compound ethylenediaminetetraacetic acid EDTA refers to the chelating agent with the formula (HO2CCH2)2NCH2CH2N(CH2CO2H)2. EDTA forms especially strong complexes with Mn(II), Cu(II), Fe(III), and Co(III) In food application disodium EDTA is added as preservative to prevent catalytic oxidation by metal ions or stabilizer and for iron fortification Approved by the FDA as a preservative in packaged foods, vitamins, and baby food Oral exposures (and inhalation) have been noted to cause reproductive and developmental effects

BHA    

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Butylated hydroxyanisole (BHA) is a phenolic antioxidant Phenolic antioxidants prevent rancidity of fats and oils in food by protecting against lipid oxidation. BHA is able to stabilize free radicals by acting as free radical scavengers, further free radical reactions are prevented When the food additives amendment was enacted (1958), BHA and BHT were listed as common preservatives considered generally recognized as safe (GRAS). GRAS regulations limit BHA and BHT to 0.02 percent or 200 ppm of the fat or oil content of the food product. Both BHT and BHA have been removed from the GRAS list and subjected to tolerances BHA is also used as a preservative for dry foods, such as cereals. FDA limited BHA to 50 ppm of the total product. Studies have suggested that at very high levels in the diets of laboratory animals, BHA could cause tumors in rats, mice and hamsters, and liver tumors in fish. The National Institutes of Health considers BHA reasonably anticipated to be a human carcinogen.

BHT   

Butylated hydroxytoluene (BHT) is a phenolic antioxidant Oxygen prefer to react with BHT rather than lipid itself – protecting against lipid oxidation. Although not toxic itself, BHT may interact with other substances:   

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Protects against toxicity in some cases Potentiates toxicity in others For example, in animal studies BHT was demonstrated to be protective against mutagens such as benzopyrene and carcinogens when given during or before exposure to benzopyrene, but enhances toxicity when given after exposure.

Some beneficial health effects of BHT:    

There are reports that BHT inhibits formations of some types of tumors. Protective against carbon tetrachloride poisoning. There is some evidence that it slows aging in mice Research is underway concerning the use of BHT in AIDS treatment

Formaldehyde 

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An aqueous solution of formaldehyde can be useful as a disinfectant, as it kills most bacteria and fungi (including their spores) It is also used as a preservative in vaccinations. In medicine, formaldehyde solutions are applied topically to dry the skin, such as in the treatment of warts The International Agency for Research on Cancer (IARC) has determined that occupational exposure to formaldehyde causes nasopharyngeal cancer in humans Formaldehyde has been banned in cosmetics in both Sweden and Japan

Glutaraldehyde 

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Glutaraldehyde is a colorless liquid with a pungent odor used to disinfect medical and dental equipment – solution of 0.1% to 1.0% concentration may be used for system disinfection and as a preservative for long term storage Also used to kill insect – as insecticide It is also used for industrial water treatment and as a chemical preservative However, it is toxic, causing severe eye, nose, throat and lung irritation, along with headaches, drowsiness and dizziness

Methylchloroisothiazolinone      

Methylchloroisothiazolinone is a preservative with antibacterial and antifungal effects It is effective against gram-positive and gram-negative bacteria, yeast and fungi It is found in many water-based personal care products and cosmetics It is also used in glue production, detergents, paints, fuels and other industrial processes It was first used in cosmetics in the 1970s In high concentrations it can cause chemical burns and it is a skin and membrane irritant and so it was largely removed from most cosmetic products except for those with only short duration skin contact such as rinse-offs

Natural Preservatives 

Organic Acids    

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These have been used for a long time as food preservatives and are antimicrobial in nature They are primarily used to prevent mold growth Organic Acids are readily available, easy to use and are very inexpensive Basically, the ability of an Organic Acid to prevent the growth of micro-organisms depends upon the pH of the foodstuff Therefore, some food products use a combination of organic acids so that the food will not grow fungi over a range of pHs Organic Acid preservatives may affect food pH slightly Organic acid do not have any toxic, carcinogenic, estrogen mimic or mutagenic properties

Natural Preservatives 

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Citric Acid  Found in citrus such as oranges, lemons and limes, Citric Acid is sour tasting. It is added to some food stuffs such as candy and soft drinks to make them sour. So not only is it used as a preservative, it's also a flavoring agent. It is also used to adjust pH. Benzoic Acid (BA)  First isolated from Styrax benzoin, a tropical tree, many types of fruits including strawberries & drupes have Benzoic Acid in them  BA is also found in cheese, spices such as cinnamon, clove & nutmeg, teas, cocoa, mushrooms and honey.  Like other organic acids, BA is used to prevent the growth of fungi & bacteria. It is added to fruit juices, soft drinks, pickles and other similar foodstuffs.

Natural Preservatives 

Sorbic Acid 

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Propionic Acid   

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Originally isolated from Mountain Ash (Sorbus sp.) berries, Sorbic Acid is used to prevent the growth of molds in cheese, wine, fish, margarine Another name for Sorbic Acid is "sorbates". Fermented products such as Swiss cheese & yogurt may have a high concentration of Propionic Acid Propionic acid is produced naturally in the digestive tract and is a natural component of sweat Propionic Acid is typically used in bakery goods, breads, meat, meat products and pizza. It is not used in many other foodstuffs due to it's strong odor.

Acetic Acid   

The simplest organic acid, this is primarily used to adjust pH. Most people know Acetic Acid as vinegar. Acetic acid is a byproduct of fermenting fruits and grains

Natural Preservatives 

Vitamin C (Ascorbic Acid)    

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Not only a necessary nutrient, Vitamin C is also an inexpensive food preservative Ascorbic Acid is water soluble and is a good anti-oxidant and anti-fungal compound It is also tart or sour and is used as a flavor enhancer Humans, primates and other animals have lost their ability to synthesize their own Vitamin C, and this is why it is an essential vitamin. Obviously, this is a very safe food & feed preservative. DID YOU KNOW? • Vitamin C and Vitamin E work together in the body. Vitamin C 'recharges' Vitamin E, so that Vitamin E can work again as an antioxidant quenching free radicals which protects cells from damage

Natural Presevatives 

Tocopherols (Vitamin E)    

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There are four tocopherols: Alpha, Beta, Delta & Gamma Alpha Tocopherol accounts for 80% of the activity of Vitamin E but Gamma Tocopherol is also biologically active Most Alpha Tocopherol on the market is chemically synthesized Natural tocopherols are all of the D or biologically active form, whereas synthetics are a 50:50 mix of D:L and therefore only have half the activity of natural E Vitamins. Tocopherols preserve food by preventing oxidation and oils from going rancid Typically, when used as a food preservative (versus using tocopherols for vitamin nutrition), the mix will contain little Alpha Tocopherol and more of the other Tocopherols