Genetic improvement of the chemical structures of saponin components in soybean seeds

Abstract

Dailyintake of soybean processed foods appears to be one of the factors responsible for the health and longevity of the Japanese. Soybeans contain a variety of functional food components, among which soybean saponins are a subject of increasing research interest. Saponins in the soybean [Glycine max (L.) Merr.; 2 n = 40] can be divided into two groups, group A and DDMP-conjugates. Group A saponins confer an undesirable taste to soy-based foods. However, DDMP saponins and their degraded compounds (groups B and E saponins) exhibit manyhealth benefits. These characteristics depend on the chemical structure of the saponin molecules and the total amount being ingested. Reducing the saponins with undesirable characteristics and increasing those exhibiting health benefits would contribute to the improvement of soybean-based foods. The composition of soybean saponins in soybeans is complex and depends on the variety and the part of the seed examined (e.g. hypocotyls and cotyledons). We previouslyreported that saponin composition in the soybean is regulated by11 genes on 5 loci. These genes control the utilization of soyasapogenol glycoside substrates and the oxidization of aglycone structures. The wild, annual soybean [Glycine soja (Sieb. & Zucc.); 2n = 40], a progenitor of cultivated soybean cultivars, is cross-compatible with the soybean and can produce fertile F 1 plants. Screening of wild and cultivated soybean genetic resources for saponin content and composition is an excellent tool for identifying lines that have a desirable taste and health benefits. This report reviews and summarizes recent research on genetic improvements to soybean saponin chemical structure.