Analysis of Free Sugars in Soybean Seed and Soybean Oligosaccharide Syrup by High Performance Liquid Chromatography

The compositions of free sugars in soybean seeds and soybean oligosaccharide syrup were investigated through high performance liquid chromatography and enzymatic hydrolysis with β-galactosidase. A Sugar-D column was used with aceto-nitrile-water solution (75:25, V/V) as the mobile phase at a flow rate of 1 ml/min, and a refractive index detector was used for the detection of sugars. Under such conditions, it ensured good separation for the sugars with stable baseline. The relative standard deviations and recovery rates were between 1.0% to 2.0% and 96.7% to 106.7%, respectively, for fructose, sucrose, melibiose, raffinose, and stachyose. Through the analysis, we found that both soybean seed and soybean oligosaccharide syrup contained fructose, sucrose, melibiose, raffinose, stachyose, and two unknown substances, while the latter also contained glucose (galactose) and another unknown compound which was inferred as manninotriose based on the result of α-galactosidase degradation. The growth activator of bifidobacterial in soybean oligosaccharide syrup was mainly manninotriose and stachyose.