Structural characteristics of oligosaccharides from soy sauce lees and their potential prebiotic effect on lactic acid bacteria

Oligosaccharides have attracted much attention due to the beneficial health effect on human beings. Oligosaccharides were extracted from soy sauce lees (SSLO) and were purified in this work. It was a mixture of oligosaccharides, which accounted for 80.5% of the total weight, and free monosaccharides. Only two monosaccharides, xylose and mannose, were detected in the molecular chain of SSLO. Their relative molar percentages were 53.2% and 46.8% for the oligosaccharide and monosaccharide fractions, respectively. A dose-dependent behaviour was observed for the growth promoting effect of SSLO on Lactobacillus bulgaricus and Streptococcus thermophilus. When 200 μg/ml of SSLO was applied, the L. bulgaricus concentration was 15.7-fold higher than the control, whilst the S. thermophilus concentration was 34.7-fold higher than the control. The analysis of DPPH radical scavenging activity indicated poor antioxidant activity of SSLO. It also suggested that the prebiotic effect was not correlated with antioxidant activity.