Soy has long been a valued food ingredient because of its protein-rich composition and its nutritive and disease-preventive qualities. In recent years, as new data has documented the health benefits of soy, consumer interest in soy-based foods has flourished. This humble legume is the only nutritionally complete plant protein containing all nine essential amino acids needed for human growth and health, in an easily digestible form. Its packed with high-quality protein with minimal fat, and contains heart-healthy polyunsaturated omega-3 fatty acids along with fiber, potassium, folic acid and iron. Its natural that food processors want to incorporate this wonder ingredient in all types of food products. Previously, soy products appeared mainly in the produce and dairy sections, but today, shoppers can find soy-based products in many aisles of the grocery store. Thats because many ingredient companies now offer a wide range of soy ingredients, including beverage bases, grits, bits, flakes, hulls, meal, butter, oil, powder, TVP/TSP and protein isolate, as well as the traditional tofu and tempeh. This gives processors many formulating options for adding the nutritional benefits and functionality of soy to prepared foods.

New developments in twin screw extrusion processing technology have given snack and breakfast cereal processors a practical tool to incorporate soy into cereal-based products. Soy flours, isolates, and concentrates are blended with other ingredients and cooked in a continuous process. Extrusion provides many opportunities for savvy processors to add health and nutrition claims to snacks and breakfast cereals traditionally made from corn, wheat, rice, bran and oats.

Label claims for soy-enhanced snacks and breakfast cereals must be in accordance with Title 21 of the Code of Federal Regulations Part 101 Section 82. There are three options for processors: Health claim; Nutrient content claim; and  Stucture/function claim.

 Health claim

According to FDA, " To bear the soy protein/coronary heart disease health claim, foods must contain at least 6.25 grams of soy protein per reference amount customarily consumed."
The food must also be low in saturated fat and cholesterol to satisfy this requirement. Once these requirements are satisfied, the label claim may read as follows: "25 grams of soy protein a day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease. A serving of [name of food] supplies _____ grams of soy protein."

"Diets low in saturated fat and cholesterol that include 25 grams of soy protein may reduce the risk of heart disease. One serving of [name of food] provides ______ grams of soy protein."

If the food also contains protein from other sources, the burden of proof for label claims falls on the food processor, as stated; FDA requires manufacturers to have and keep records to substantiate the amount of soy protein in a food that bears the health claim and contains sources of protein other than soy, and to make such records available to appropriate regulatory officials upon written request.

Nutrient content claim

If foods do not contain sufficient levels of soy to qualify for a health claim, they may qualify for a nutrient content claim, as follows: While a health claim about soy protein refers to a claim discussing the positive relationship between consumption of soy protein and reduction of cardiovascular risk, a "nutrient content" claim is a claim about the level of soy protein in the food (such as a label statement that indicates that a particular product is an "excellent source of soy protein"). Nutrient content claims are regulated by FDA separately and may appear anywhere on the label. A product bearing a health claim for soy protein may also bear a nutrient content claim if the product meets the requirements for both claims.

Structure/function claim

According to FDA, these claims are statements that describe the effect a dietary supplement may have on the structure or function of the body. A structure/function claim is one that discusses what a food substance does metabolically, so long as the relationship between that metabolic function and a potential disease is not known or is not clear. Structure/function claims, such as, "fiber makes one regular" or "calcium is used to build bones," are permitted on any food substance at any time and are not governed by any regulations other than the fact that the claim must be true.

Breakfast cereal and snack processors can easily incorporate soy into their products. Low-fat soy flour, processed by either a mechanical extraction process or high-pressure carbon dioxide extraction, is commonly used. Defatted flour products appear in enzyme-active or toasted forms, and in different particle sizes, from ultra-fine powders (soy flour) to more-coarse soy grits. Further processing soy flour produces dry, textured nuggets. These products can contain up to 55% protein content. Functionally, these ingredients are shown to improve product taste, texture and moisture while boosting protein values. Soy isolates and soy concentrates are also often used. Soy is typically used as 25% of the dry base, yet some products incorporate up to 50% of the dry base.

Expanded snacks
Using twin-screw extrusion, processors can create a variety of expanded snacks, from light, crispy puffs with open cell structure, to denser, more-crunchy varieties, simply by varying the ingredient mix and the processing parameters. Soy will affect expansion indices, as it tends to decrease expansion. Therefore, in creating expanded products, the process must be adjusted to compensate for variation of the recipe, reconfiguration of the screw profile, die, etc. Expanded snacks are produced at higher efficiencies and dramatically increased capacity on twin-screw extruders, compared to single-screw machines. In this area, improvements in technology are literally reshaping the product. Advances in die and cutter designs are giving processors an entirely new set of templates for creating innovative product shapes, far from the traditional varieties of puffed balls, twists and curls. Plus, recent developments in extruder design and control allow more textures and density combinations.

In a typical expanded snack production line, dry ingredients are blended and metered into the extruder barrel simultaneously with the liquid ingredients. Homogeneous dough is created by the co-rotating action of the screws. The extrudate is subjected to heat and shear to gelatinize the starch and cook the product. Finally, the positive pumping action of the screws forces the dough through the die. Expansion takes place as the steam in the extrudate flashes off. The product is shaped at the die by a combination of expansion, die aperture and die-face cutting, or formed into strands for post-extrusion shaping and cutting. The extruded snack enters a belt dryer, which decreases the moisture content. Finally, the product enters a coating drum where it receives a liquid flavor coating, or it may be dusted with a flavored powder.

Crunchy nuggets and inclusions

In addition, the twin-screw extruder can process soy-crisp ingredients that enhance products, such as nutrition bars, breakfast snacks, granola mixes, and specialty bakery products, with the nutritional benefits of soy in the form of consumer-preferred crunchy nuggets and crisps.  Proprietary soy inclusions with a variety of attributes (size, color, density, texture) can be processed for many different products.

Coextruded products

Coextruded snacks and breakfast bars, with crisp cereal shells and soft fillings, delight consumers of all ages. Processors can incorporate soy flour into sweet or savory coextruded products, and add a healthy benefit to these consumer favorites. Pre-engineered dies let processors create many shapes, such as bars, pillows, nuts, balls, and long and short ovals. Fillings range from cream, jelly, and fruit purèe for sweetened snacks, to cheese and meat for savory products.

The coextrusion production line starts with dry-ingredient blending in a separate mixing vessel. The dry mix is fed to the extruder with the liquid ingredients. At this point, the screw flights are an open design to form amalgamous dough. The screw flights quickly become more severe, generating mechanical heat and shear within the product. Heating and/or cooling circuits in each section of the extruder barrel precisely control processing temperatures. Meanwhile, the soft filling is prepared and held in an agitating tank. As processing is completed, the extrudate enters the coextrusion die, which concurrently forms and fills the product.

Upon exit from the extruder, the malleable product is shaped and cut. A variety of flattening units, crimping rollers, pulling belts and stamping systems accurately create the desired profile of the co-extruded product. Next, the product may enter a belt dryer to reduce the moisture content, if required. Multi-belt drying systems are used for small products, and single-belt dryers for longer products. Finally, a liquid flavor coating can be applied, or the product can be enrobed in a sweet or savory coating.

Flaked products

Today, consumers increasingly munch on snack mixes and cereal flakes for between-meal snacks. Snack manufacturers can easily include soy-based flakes to snack blends with twin-screw extrusion technology. Extruded flakes require a fraction of processing time and energy compared to traditional flakes, and they exhibit similar quality and flavor profiles.

To process extruded flakes, dry ingredients, including grits, sugar and salt, are mixed and conveyed to a preconditioner, which hydrates and heats the mixture to commence gelatinization. The partially cooked product is fed to the twin-screw extruder. Inside the extruder, the twin rotating screws mix the extrudate, creating heat and shear to perform complete gelatinization. Malt syrup is injected directly to the extrudate through ports in the extruder barrel. Heating and/or cooling circuits in each section of the extruder barrel precisely control processing temperatures. This process forms a dense-phase extrudate, which will mimic traditional grits when processed through a flaking mill.The fully cooked product is forced through a die, which forms continuous strands. After a short cooling period, the strands are cut into nibs. Strands may be cut into various sized nibs; therefore, the size of the flake is no longer dependent on the size of the grit. After cooling, the pellets are flaked in a flaking mill and transferred to a toasting oven. A coating can be applied to add a sweet flavor or vitamin enrichment, followed by a final pass through a belt dryer-cooler.

Snack pellets

Pellet-based snacks (nonexpanded half products that require a heating step for expansion prior to consumption) offer the consumer the freshest snacks at the retail outlet. Snack pellets produced on twin -crew extruders offer higher throughputs and improved product quality. In addition, new ingredient combinations and cooking techniques are creating a new range of textures for third-generation snacks that give processors a marketing edge in providing exciting snacks for trend-hungry consumers.

Double take on extrusion technology

Consumers want it all when it comes to snack and breakfast foods: freshness, flavor, variety and nutrition. Manufacturers want processing equipment that can help them supply these dynamic markets. Twin-screw extrusion processing technology is a solution, giving processors the processing power and flexibility to produce expanded snacks and cereals, filled products, inclusions, flakes, snack pellets, breakfast bars and more, continuously, on automated equipment, and at high production efficiencies. The twin-screw extruder has established itself because of the requirements of quality (regarding processing of the final product), and process productivity and flexibility. Extrusion- processing advances have enhanced product textures (defined by their cellular structure) and made it possible to incorporate dramatically increased percentages of protein-rich soy into products, improving their consumer appeal. With new generation twin-screw extruders and improvements in die-flow design, higher throughputs are available on smaller extruders, optimizing investment and operating costs.

Twin-screw extrusion has opened up the processing opportunities for making products that were not possible using the single-screw extruder. Single-screw extruders are the simplest and the cheapest on the market, but their process functions are limited, particularly when the formulations become complex and require a high degree of mixing, or when flexibility and high quality products are desired. Twin-screw extruders work in a different way: The interpenetration of the screws creates a positive movement of the material, although the machine is not filled. Therefore, the throughput and screw speed are independent within a certain range of variations. When the flow is restricted by the screw configuration (counter-thread, mixing elements, die), material accumulates upstream, creating a working section (an active area where the material is worked by shearing), which contributes to its physical and chemical transformation and its heating by viscous dissipation. When compared with single-screw processing, twin-screw technology allows more efficient mixing, heat transfer, residence time distribution and, consequently, the shear-time-temperature, all essential in processing soy-based recipes.

Processors can get on the fast track to producing soy-enhanced foods by purchasing pre-engineered production lines. Turnkey systems provide all equipment from start to finish, including bulk ingredient storage, dry material feeder, preconditioner, twin-screw extruder, former, cutter and dryer, plus all equipment interfaces. As processors discover the benefits of twin-screw extrusion for processing soy-based products, this versatile and flexible processing tool may well become the way of the future.

Clextral  is a division of diversified industrial group Legris Industries and a world leader in extrusion for applications in food processing, chemicals, plastics and specialty papers. The company specializes in the design, manufacture, assembly and maintenance of industrial equipment and turnkey production lines.

Mike Shaw, Eastern regional manager, Clextral Group, works on food-extrusion projects and test-plant consulting, and facilitates co-processor projects for food processors. He holds an engineering degree, M.B.A. in marketing, and has 15 years food industry experience in extrusion, baking and packaging. For more information, email [email protected]