Optimization of soybean protein qualities.

There are a number of antinutritional factors present in soybean; among tho se factors, the major part are heat-labile. Raw ripe seeds are not edible f or humans and animals, and have low nutritional value for use as foods or f eeds. Soybean protein resources require moist heat treatment to inactivate protease inhibitors, phytohemagglutinins and other heat-labile antinutritio nal constituents, as well as to transform raw proteins into more readily di gestible forms. Although thermal treatment of soybean is necessary, overhea ting will cause a loss in nutritional quality by reducing the Protein Effic iency Ratio (PER); it adversely affects also the functionality of soy prote ins in food manufacture. Heat processing of soybean needs not to be aimed t o total deleterious components inactivation; heat treatment should be based on inactivation of the most heat-resistant factors referred to as the "lim iting factors" of the process. In general, the degree of improvement of nut ritive value of soy proteins parallels the inactivation of antinutritional factors. Moisture content, type and heating intensity, heating temperature, pH and ionic strength of the solution and the particle size of soybean pro ducts play a very important role influencing the inactivation of antinutrit ional factors and increasing the nutritional value. Extraction of oil by no n-polar solvents, elimination of solvents from defatted flakes at low tempe rature and specific processes of drying such as freeze-drying, spray drying , rotative vacuum drying, etc. can improve the Protein Dispersion Index (PD I) of the defatted soybean proteins. The defatted soybean flakes for human food use have to keep a high PDI. The development of soy food protein indus try has been driven primarily by the ability of soy products to meet functi onal needs in processed foods at lower cost than animal-origin ingredients. From the industrial point of view, the functional properties of soybean pr oteins are very important for increasing the versatility and utility in the system of food and feed manufacture.