Nutritional improvement of food proteins by enzymatic modification, especially by plastein synthesis reaction.

The present paper reviews our recents studies on the plastein reaction applied to improve nutritional quality of conventional and unconventional proteins, with special emphasis on the papaincatalyzed incorporation of essential amino acids (used in ethyl ester form) into the proteins : L-methionine into soybean protein, L-lysine into wheat gluten and L-tyrosine into fish protein (after removal of phenylalanine). The paper deals also with an attempt to improve proteins extracted from the photosynthetic microorganisms, Spirulina maxima (a blue-green alga), Rhodopseudomonas capsulatus (a non-sulfur purple bacterium) and Trifolium repens L. (a type of white clover) by way of incorporating simultaneously the three amino acids, L-methionine, L-lysine and L-tryptophan. This process, when properly carried out, can produce plasteins whose essential amino acid patterns have approximated the FAO/WHO suggested pattern (1973). Besides the plastein reaction, its novel modification has been developed, which will be more conveniently applied to a larger-scale process for the amino acid incorporation. A brief discussion is added in this regard.