Characteristics of Bacillus subtilis HNMY-13 and HNMY-15 strains in aflatoxin B1 degradation and Astragalus bio-transformation

Astragalus of traditional Chinese medicine (TCM) and Bacillus subtilis are extensively used in animal feed and for production of various fermented compounds. In order to observe the characteristics of HNMY-13 and HNMY-15 B. subtilis strains, this study focused on the optimization of parameters in liquid fermentation of the two strains in aflatoxin B1 degradation, and Astragalus polysaccharide yield. The optimal parameters: degradation of aflatoxin B1, the bacterial count, and the Astragalus polysaccharide yield analysis were examined in this study. It was shown that the percentage degradation of AFB1 by HNMY-13 and HNMY-15 strains were 80.48 and 79.55% at 37°C, and 80.66% and 81.34 with pH 7.0. The percentage degradation by HNMY-13 was 88.07% after 48 h fermentation and by HNMY-15 was 84.81% after 60 h fermentation, respectively. The viable count of fermented sample was 8.8×108 and 7.6×108 CFU·mL-1 using HNMY-13 and HNMY-15 strains, respectively. The polysaccharide yielded by HNMY-13 was 4.93% at 48 h which is 1.7-fold higher than that of the control group, while polysaccharide yielded by HNMY-15 reached peak of 3.54% at 60 h. In conclusion, HNMY-13 and HNMY-15 of B. subtilis promote production of Astragalus polysaccharide in the process of liquid fermentation and can also degrade aflatoxin B1 significantly; hence the combination could form a potential feed additive for animals.   Key words: Astragalus, Bacillus subtilis, liquid fermentation, aflatoxin B1, polysaccharide.