Effect of Bacillus cereus Br on bacterial community and gossypol content during fermentation in cottonseed meal

Abstract

To define new methods for the detoxification of free gossypol (FG) within cotton seed meal (CSM), FG during CSM fermentation with Bacillus. cereus Br were measured. Four conditions were studied: CSM inoculated with Br (Br + CSM), CSM without any inocula (CSM), sterilized CSM inoculated with Br (Br + sCSM), and sterilized CSM without any inocula (sCSM). Samples were taken at various times during the fermentation and the contents of free gossypol (FG), crude protein (CP), and amino acids were measured. The polymerase chain reaction and denaturing gradient gel electrophoresis (PCR-DGGE) method was used to analyze the changes in bacterial community structure during the fermentation. After the Bacillus. cereus Br was inoculated into CSM, the FG concentrations decreased to the minimum level of detection at 12 h, while CP and amino acids concentrations reached maxima at 18 h. The initial content of FG and CP decreased significantly when the CSM was pre-sterilized, and decreased to minima after 12 h fermentation. The changes in bacterial community structure mirrored the changes in FG and CP. B. cereus Br was dominant in the CSM + Br group during the first 12 h of fermentation, after which Br growth was inhibited by native bacteria in CSM. In contrast, B. cereus Br was always dominant during fermentation of autoclaved CSM. These results suggest that the native microbes of CSM significantly influenced the detoxification rate, and inhibited B. cereus Br growth during fermentation. But pre-sterilization of CSM significantly affects the FG content and quality of CSM. The B. cereus Br was capable of detoxifying FG from CSM, and the optimal time of fermentation was 18 h. Key words: Bacterial community, free gossypol, detoxification, fermentation, cottonseed meal.