Extrusion Process

UNEDITED

SESSION 2 / PAPER 6

NEW TECHNOLOGICAL SOLUTIONS – EXTRUSION PROCESS By Mian N. Riaz. Ph.D. Food Protein R&D Center, Texas A&M University

ORGANISED BY

NEW TECHNOLOGICAL SOLUTIONS – EXTRUSION PROCESS Mian N. Riaz. Ph.D. Food Protein R&D Center, Texas A&M University

Abstract Extruded snacks have the greatest potential for growth among the snack foods category. Extrusion technology provides the opportunity to process a variety of snack products by just changing a minor ingredient and processing condition on the same machine. Several different shapes, textures, and colors of snack foods are possible by using an extruder. The extrusion process can produce innovative snacks which capture the consumer’s imagination. An example of this is three dimensional snacks with a variety of shapes including animal, cartoon, and alphabet. Producing a successful snack is a fine balance between the consumers’s needs, like tastes and interests vs. a manufacturer’s production abilities, economics and quality control.

Designing snack foods today can be a complex process to meet changing consumer’s tastes and expectations. The consumer’s demand for “good for your health” “rich source of soy protein” and “unique flavor“ snack foods leads to the elusive search for something unique that also appeals to a wide variety of peoples. Most snack manufacturers use some form of existing technology as the basis for creating snack products, but incorporate variation that increase the resulting snack’s health image appeal by lowering fat and calories or adding nutrients. This can be accomplished by using extrusion technology.

Background: Designing snack foods today can be a complex process to meet changing consumer’s taste and expectation, e.g. “good for your health,” “rich source of soy protein” “offering a unique flavor” and the elusive search for something unique that also appeals to a wide variety of people. Most snack manufacturers use some form of existing technology as the basis for creating snack products, but incorporate variation that increase the resulting snack’s health image appeal by lowering fat and calories or adding nutrients (1). This can be accomplished by using extrusion technology. What is Extrusion? Food extrusion is a process in which a food material is forced to flow, under one or more varieties of conditions of mixing, heating and shear, through a die which is designed to form and/or puff-dry the ingredients (2). The food extruders can be visualized as a high temperature short time (HTST) device that can transform a variety of raw ingredients into intermediate and finished products. During extrusion, the cooking temperature could be as high as 180-190 C, but residence time is usually 2040 seconds (depends on types of extruders and speed of the shaft). For this reason the extrusion process could be called as HTST process. It is very important to understand the extrusion terminology, since each manufacture likes to use their own terminology based on their equipment. Extrusion technology provides several different advantages over the traditional methods of food and feed processing. Some of the advantages based on Smith (3) and Riaz (4) with modification includes the following. Extrusion technology provides the opportunity to process a variety of food products by just changing a minor ingredient and processing condition on the same machine. Several different shapes, texture, color, and appearances can be processed by minor changing in the hardware and processing conditions. Extrusion process is energy efficient, and low cost compared to other processes. Presently, most of the extruders are available with automation, which can increase the productivity. Since extrusion process is considered HTST the product quality is much better than other processes, since cooking is done in a very short time and less destruction takes place to the heat sensitive ingredients. It is very easy to scale up the extrusion process for larger installation. Types of Extruders: In the past the most common extruder in the snack food production have been the single screw extruders. Still most of the expanded snacks are made from single screw extruders because of the economic point of view. Many common snack foods such as fried or baked are corn base and produced by single screw extruders. However, with the new and complex new ingredients, different snack shapes and color the twin screw extruders have begum to take place for single screw extruder. Snack products like half products or third generation snacks, may require more advance extruders like, twin screw.

International Palm Oil Trade Fair & Seminar (POTS) , 21 – 24 Nov 2006

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Snack Consumption Patterns: The snack food market is constantly changing relative to product types, and although most snacks are not primarily consumed for their nutrients, many snacks are made with nutrition in mind. The snack food industry is experiencing extraordinary changes from the consumer’s point of view. Consumers want snacks to not only taste good, but also smell good, feel good, and look good. Snacks should give the consumer a homemade/fresh feel. Some of the snacks are developed with a special theme in mind like world soccer. These snack pellets are soccer ball shaped, which on frying or microwaving become soccer balls. Snacking overall is on the rise in the US owing to an increasingly hectic lifestyle with more time spent at work. Currently more than two-thirds of US women work outside the home and the number of two income families in the US has doubled over the last 20 years. Snacking is increasing from factors such as increases in one-person households, and more school age children obtaining their own meals and refreshments, a highly mobile population, and availability of snack foods in vending machines and convenience markets. Snacking now provide approximately 30 percent of many American’s daily calories (5). Various products which were once consumed mainly on impulse are becoming accepted as side-dish items, for example, corn chips or potato chips served in place of mashed potatoes. The established position of snack foods in the diet is demonstrated by the continuous growth in sales. In the last ten years, changes in life-style and eating patterns have led to a gradual increase in demand for snack foods. The pattern of snacking in different countries can be affected by several factors such as the lifestyle in each area, the economic climate, rival foods and public receptiveness of current views on nutritional matters. Snacks can provide an increased dietary intake of essential amino acids and other nutrients for developing countries. Types of Snack Foods: Each snack processor may use a specific unit operation and somewhat different technologies to produce unique snacks. There are many ways to classify the snacks. Snack manufacturers uses three main terms to identify the snacks: 1) first generation snacks: In this category all the natural products used for snacking, nuts, potato chips and popped popcorn are included; 2) Second generation snack: Majority of the snacks fall in this category. All the single ingredients snacks, simple shaped products like corn tortilla chips and puffed corn curls and all directly expanded snacks are included in this category; 3) Third generation snacks also called half-products or pellets: In this category, multi ingredients formed snacks and pellets, made by extrusion cooking are included.

Extruded Snacks This category has the greatest potential for growth among the snack foods. The snacks can be made to produce innovation which captures the consumer imagination. Some of the examples are three dimensional snacks, a variety of animals, cartoon, International Palm Oil Trade Fair & Seminar (POTS) , 21 – 24 Nov 2006

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and alphabets shapes etc. Producing a successful snack is a fine balance between the consumers’s needs, like tastes and interests vs. a manufacturer’s production abilities, economics and quality control. Raw material cost play an important role in the finished product’s selling price. Therefore, it is an advantage to use the lowest cost raw material to produce a successful snack.

Expanded Snacks The majority of extruded snacks are in this category. This group is also referred as “collet” or “second generation snacks”. In general, expanded snacks are made on high-shear extruders. These are high-fiber, high-protein, and low calories snacks. Some examples are corn curls, onion rings, three dimensional snacks, and potato sticks. These types of snacks can be seasoned with a variety of different flavors, oils, salt, sugars, etc. The quality of an expansion-cooked product depends upon the conditions of operation of the extruder and the main raw material used in the formulation. Several other factors can influence the degree of puffing of snacks during extrusion, i.e. amount of moisture in the feed material, dough residence time in the extruder barrel, and cereal particle size.

Fried Collets These are the most familiar extruded snacks in the market. A special die arrangement gives the product a twisted puffed shape. These collets are made on collet extruders. The product is then fried in vegetable oil, and coated with cheese and some other flavor. During frying the moisture level reduces from 8% to 1-2% in this product. The most common material used for fried collet is corn meal. Some other cereal grains can also be used for this type of product.

Baked Collets Baked collets are another example of the expanded extruded snacks. This include products such as baked corn curls, onion rings and potato sticks. Baked collets can be made with different cereal grains and tuber flours. Protein, fibers, cellulose, and bran can be blended with cereal grain up to 20% to make healthy snacks (6). Potato sticks usually made by mixing potato flour with corn or rice flour.

Third-Generation Snacks Third generation snacks (3G) snacks, also referred to as “half products” or pellets provide an alternative to fully prepared puffed snack foods. Third generation snacks or half products are extrusion cooked, and formed at low pressure to prevent expansion, and then dried to a final moisture content of about 10% to form a glassy pellet. In developing third generation snacks, "half" of the process is completed to prepare "pellets" which are shelf-stable for periods of up to a year without refrigeration, provided they are properly packed to retain their moisture. Many types of proteins and protein enrichments may be added to third generation snack type recipes such as meats (whole fresh shrimp, fresh chicken, beef, etc), dairy products (cheese, yoghurt, milk solids) and legume proteins (soy, pea, bean). Up to 30 to 35% levels may be added and still maintain high quality final products (7). Several minor ingredients have International Palm Oil Trade Fair & Seminar (POTS) , 21 – 24 Nov 2006

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very useful effects on the texture, quality and flavor of the final products. Salt is very useful in assisting with uniform moisture migration throughout the third generation pellet after drying during the moisture equilibration period. Baking soda will give special flavor and textural attributes to the finished products after frying, puffing or microwaving. Oils or emulsifiers reduce stickiness during cutting and other processing step (8). Drying is very critical in the production of good quality third generation snacks. Proper drying will reduce the moisture content of the pellet to approximately 12 percent. Temperatures of 70-95 C and retention times of one to three hours are required. These products are economical to run and have built-in-marketability due to their high-bulk density. Third generation snacks can be prepared in homes or restaurants. Unlike typical snack foods, half-products do not yet contain oil that can oxidize to give off-flavor to the products. These pellets can be shipped from a central manufacturing distribution point, held until needed for the market, and then puffed, flavored and packed fresh and locally. New variations of the third generation snacks expand using infrared heating, hot air, or microwaving. The use of hot air systems reduces the oil uptake that occurs in frying and allows a controlled addition of oil to be made as required for flavoring. With consumer concerns about fats and oils, a half product snack that expands using hot air, offers snack food manufacturers an oil free snack with perceived health benefits. Elimination of frying oils reduces calories and allows a marketing opening for snacks with a "lite" image. With the multidimensional snack system, a wide range of raw ingredients can be used to blend together to make an excellent formulation for many types of third generation snacks. The extruder feed must contain a high level of starch to maximize expansion of the collet during exposure to hot oil or air. Levels of 60% or less total starch in the formula give only slight expansion in the puffing step and yield a final product with a crunchy, hard texture. Wheat, corn and tubers are widely grown crops in developing and industrialized countries, and they are cheaper and easily available in the market than the other cereal crops.

Co-Extruded Snacks This is a relatively new technology introduced in 1984 for the snack food industry. In this process two different materials are extruded from one die. The two materials can come from two extruders or from one extruder and one pump. This process can produce a snack with two different flavors, or two textures or two colors. The most common snack produced by co-extrusion is a cereal based outer tube with a cheese filling inside. There are three basic types of co-extruded snacks in the market; cereal-based tubes with cereal-based fillings, cereal-based tubes with fat-based fillings, and cereal-based tubes with water-based filling. The shelf life of these snacks is limited, because of migration of moisture and/or oil from the filling to the outer shell. In conclusion, snack can be processed by variety of different methods and techniques. Several new raw materials containing nutraceutical and functional properties are being introduced in the market every day for snack food products. Snacks can be made with a combination of different raw materials containing different properties. The role of snacks in a healthy life style is only starting to be developed. International Palm Oil Trade Fair & Seminar (POTS) , 21 – 24 Nov 2006

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The recognition of snacks as healthful will increase as industry changes products from merely good tastes to nutritious.

References: 1. L. Kuntz. Creating healthful salty snacks. Food Product Design. 1996. Vol. 6(9).3156. 2. J. L. Rossen and R. C. Miller. Food extrusion. Food Technol.,1973. 27:46-53. 3. O. B. Smith. “Why use extrusion” Symposium on Extrusion: Process and Product Development. American Association of Cereal Chemists. St. Paul. MN., 1971 4. M. N. Riaz. Extruders in Food Application. CRC Press. Boca Raton, FL. Originally Published by Technomic Publishing, 2000. 5. M. Hilliam, Have a snack. The World of Food Ingredients. Sep. 2001, p12-14. 6. G. Huber and G. J. Rokey. Extruded Snacks. In “Snack Food” Ed. Booth, R. G. Published by Van Nostrand Reinhold, NY. 1990. P. 107-138. 7. R. Sunderland. Production of Third Generation Snacks. Cereal Food Word. 1996. (41)1:12-14. 8. G. R. Huber. Recent developments and trends in the snack food industry. In M. Riaz, L. Rooney and M. Barron Eds., Snack Food Processing Shot Course Manual. Food Protein Research & Development Center, Texas A&M University, College Station, Texas, 2002

Mian N. Riaz. Ph.D. Head- Extrusion Technology Program Food Protein R&D Center, Texas A&M University College Station, Texas, USA 77843-2476 Tel: 979-845-2774; Fax: 979-458-0019 E-mail: [email protected]; www.tamu.edu/extrusion

International Palm Oil Trade Fair & Seminar (POTS) , 21 – 24 Nov 2006

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