Molecular design of soybean glycinins with enhanced food qualities and development of crops producing such glycinins.

Abstract

Soybean (Glycine max L.) protein has a function to lower cholesterol level in human serum (Kito et al., 1993) and is one of the best plant food proteins in terms of nutritional and organoleptic qualities. However, it is usually inferior in these respects to animal proteins. For example, the amino acid composition of soybean protein does not satisfy infant requirement: sulfur containing amino acids are deficient. Improvement of nutritional value and functional properties of soybean proteins is one of major objectives in the food industry (Kinsella, 1979). Soybean proteins consist of two major components, glycinin and β-conglycinin (Derbyshire et al., 1976). Of these two proteins, glycinin is superior to β-conglycinin with regard to nutritional value (Millerd, 1975) as well as functional properties (Kinsella, 1979). Five subunits are identified as constituent subunits of glycinin and classified into two groups: group I (A1aB1b, A1bB2, A2B1a) and group II (A3B4, A5A4B3) (Utsumi, 1992). The subunits belonging to group I have better nutritional value than those of group II. Therefore, a group I subunit of glycinin is a suitable target for such improvement to create an ideal food protein. Protein engineering appears to be a promising method in achieving improvement of glycinin qualities because the primary sequence of glycinin can be modified consciously and systematically.