The most refined forms of soybean proteins are the isolates, which contain 90% or more protein.
They are prepared by removing the water-insoluble polysaccharides, as well as the oligosaccharides and other low-molecular-weight components that are separated in making protein concentrates.
Defatted flakes or flours, which have received a minimum of moist heat treatment, are extracted with water plus alkali at a pH of 7 to 8.5.
Soy concentrates and isolates provide highly concentrated protein sources, high lysine content, bland flavor, and reduction of flatulence factors and reducing sugars, and they may lead to improve overall product quality.
Several soy protein isolates have been developed for providing different functional or physical properties to meet the requirements of various food systems. The solubility of isolates ranges from 25 NSI (nitrogen solubility index) to 95 NSI.
Isolates can emulsify from 10 to about 35 mL of oil per 100 mg of protein. On the other hand, where maximum emulsifying capacity of the proteins is not needed, and where thermal thickening and gelation occurs, initial solubility may not be too critical because stable emulsions can be formed with adequate energy input.
The film-forming properties of soy protein isolates are useful in certain meat products. Applying heat and pressure causes protein films to fuse together to form a firm, continuous textured mass that can be sliced and used as meat substitutes.
Soy protein isolates vary in their ability to form gels. Some are designed to form gels while others will not form gels at 14% solids content, with salt content also affecting the gel strength.
The viscosity properties (thixotropic) illustrate again that all isolates do not have similar properties. Some isolates will have the same viscosity at 18% solids as other isolates have at only 10% solids concentration.
Uses
• Meat Food Products
• Dairy Type Products
• Bakery Products, Cereals and Pasta
• Miscellaneous food applications include brew flakes (soy flakes/grits); soups, gravies, and sauces; confections; imitation nut meats; and nonfermented oriental soybean foods (such as soymilk and tofu).
• Canned soups, sauces, and gravies often utilize soy proteins to prevent separation of ingredients and to impart thickening which is so essential to the identity of these products.
• Other product concepts entering the retail market are those in the dry grocery products category. These consist of a pouch pack or boxed instant dinner concept, using soy proteins as functional ingredient
