Effects of the Structure and Antioxidant Activity of Legume Crude Polysaccharides after Bacillus subtilis Fermentation

Eight kinds of common edible legumes were fermented by Bacillus subtilis to produce novel legume polysaccharides under the condition of fermentation temperature at 37 ℃ for 7 days, and the changes of molecular weight, infrared spectra and antioxidant activities of the crude polysaccharides before and after fermentation were analyzed. Results showed that, the fermentation by Bacillus subtilis could effectively remove impurities in polysaccharides and improve the purity of crude polysaccharides. Total sugar contents increased from 3.35%~35.63% to 16.61%~77.11% after fermentation. The content of uronic acid in crude polysaccharides significantly increased after fermentation (P<0.05), and the molecular weight of crude polysaccharides increased from 0.45~14.80 kDa to 18.00~56.56 kDa after fermentation. The infrared spectra of crude polysaccharides of beans before and after fermentation also conformed to the characteristics of polysaccharide molecules. The scavenging capacity of broad bean crude polysaccharide to DPPH free radicals was significantly improved (P<0.05). Moreover, the scavenging capacity of cowpea, red bean, mung bean, lentil, broad bean and common bean crude polysaccharides on ABTS⁺ free radicals were significantly increased (P<0.05). The reduction abilities of eight kinds of crude legume polysaccharides to iron ions were all improved after fermentation (P<0.05). The molecular weight of legume crude polysaccharides was increased and the antioxidant activity of legume crude polysaccharides was affected by using Bacillus subtilis fermentation.