Figure 17

Soy Protein Levels

Isolated Soy Protein

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Soy Concentrate

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Soy Flour

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How Soy Protein Products Are Produced | Elements of the Soybean

As the world's foremost provider of vegetable protein, soybeans offer a complete solution to your food application needs. Soy protein products come in three basic categories: isolated soy protein, soy protein concentrates and soy flour / grits. The starting point for all soy protein products is the whole soybean, which contains about 40 percent protein. As the proteins are processed and refined, each takes on different characteristics. Here's a quick overview of the basic soy protein products.

Isolated Soy Protein

A versatile soy derivative, isolated soy protein is the most refined form of soy protein and is often used in finished meat products to improve eating quality, cooking tolerance and enhance succulence. It is also commonly used in baked goods to boost nutritional value. Its most common form is powder, but can also come in granules and structured fibers. Isolated soy protein contains 90 percent protein on a dry basis (see Figure 17).

Soy Protein Concentrates

This type of soy protein is prepared from defatted soybeans by removing the water-soluble carbohydrates. Soy protein concentrates take on the flavor of the foods they enhance and tend to improve the overall quality because they retain moisture and will hold flavor through multiple cooking processes. They contain about 70 percent protein and 23 percent dietary fiber (see Figure 17). The two most common forms of soy protein concentrates are textured soy protein concentrates and powdered functional soy protein concentrates.

Textured Soy Protein Concentrate
Available in flakes, small chunks or granules, repaired soy protein concentrates maintain the texture of foods and must be hydrated. They enhance mouth-feel and provide a firm texture that remains stable through cooking, freezing and thawing. Textured soy protein concentrates are processed to resemble a form of food ingredient, such as a fiber or chunk.

Functional Soy Protein Concentrate
These fine powders provide firmness, moisture control and they are used at low levels to enhance mouth-feel. Functional soy protein concentrate can be combined with textured soy protein concentrate to provide a juicy, meaty texture.

Whole Soybeans

These are an excellent source of protein and dietary fiber and can be used in sauces, stews and soups. Soynuts, whole soybeans that have been soaked and roasted, are similar in texture and flavor to peanuts.

Soy Flour/Grits

These are the least-processed forms of soy protein and typically contain higher levels of dietary fiber. They are prepared by grinding and screening soybean flakes either before or after removal of oil. Their protein content varies from 40 percent to 54 percent (see Figure 17). They also vary in fat content, particle size and the degree of heat treatment.

Textured Soy Flour
... is made from defatted soy flour and is compressed and dehydrated. Available in flakes, small strips, chunks or granules, it maintains the texture of foods. When rehydrated, it has a texture similar to ground beef and can be flavored and fortified. Textured soy flour contains about 50 percent protein, including standard moisture content.

Protein Quality Comparisons

The Protein Digestibility-Corrected Amino Acid Score (PDCAAS) is a relatively new method of protein quality evalution that takes into account the digestibility of a food protein and the amino acide content. The PDCAAS method utilizes the amino acid requirements of humnas. It has replaced the PRotein Efficiency Ratio (PER) that considered only the amino acid requirements of rats and measured the growth of rates that were fed test proteins. The PER underestimated the value of vegetable proteins. Today, the Food and Drug Administation uses PDCAAS for food labeling in the U.S. and it is considered the desired method for protein quality evaluation.

Food Proteins Currently in Use Isolated soy protein Soy protein concentrate Egg white Casein Beef Kidney beans (canned)

PDCAAS 0.92 0.99 1.00 1.00 0.92 0.68

SOURCE: Protein Quality Evaluation, Report of the Joint Food and Agriculture Organization / World Health Organization Expert Consultation, 1989

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