Exuding Behavior of Soybean Oligosaccharides by Hot Water Immersing

Abstract

Exuding behavior of soybean oligosaccharides by hot water were studied through TLC and HPLC. Exuding oligosaccharides increased as immersing temperature increased, and the exudate was chiefly made up of sucrose, raffinose and stachyose. The ratio of these oligosaccharides was almost constant above 50°C; sucrose: raffinose: stachyose (63:6:31). However, only small amounts of the oligosaccharides were obtained below 40°C. The extension of immersing time enabled to let out larger amounts of the oligosaccharides with almost constant ratios. The amount of oligosaccharides exuded from hypocotyls alone was about 1.8 times as large in the case of 80% ethanol extraction, and 2.5 times as large as from whole soybeans in the case of hot water immersion. Hot water exudate was extracted with methanol and was separated into soluble and insoluble fractions. Eighty-four % of oligosaccharides in the MeOH soluble fraction was sucrose and 86% was stachyose in the MeOH insoluble fraction. Thus, crude fractionation into sucrose and stachyose was found to be possible. The oligosaccharide contents of 24 kinds of soybeans, including saponin Aa types and Ab types, were investigated. The result showed that Ab type soybeans had higher oligosaccharide contents than Aa type. The average sucrose content of Ab type soybeans was 4% higher. However, no difference in constituent oligosaccharide ratios was observed between both types.