Nutritional qualities of soya protein as affected by processing

Abstract The nutritional qualities of soybean proteins are basically determined by amino acid patterns, amino acid availabilities (digestibility) and contents of biologically active components. Of these factors, the last two are most affected by processing conditions, whereas amino acid analysis is least affected, although it too may be modified in those cases in which soybean proteins are fractionated. In the preparation of the large variety of soya products presently available, soybeans are subjected to many different processes, all of which are discussed. Heat treatment appears to be the process which most affects protein nutritional quality; generally, quality first increases with heat treatment due to inactivation of biologically active factors, passes through a maximum and then decreases due to destruction and/or inactivation of essential amino acids such as cystine and lysine. Other processes affect protein nutritional quality to different degrees, inasmuch as they affect amino acid analysis, digestibility and content of biologically active components. When soybean proteins are used to extend animal proteins, supplement other vegetable proteins, or in vegetable protein mixtures, nutritional quality of the combined proteins appears to be affected in the same manner as that of soya proteins alone.