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