Development of a microbial fermentation process for detoxification of gossypol in cottonseed meal

The objective was to study effects of selected fungi, carbohydrate sources, urea, heat treatment and minerals on the reduction of free gossypol (FG) levels during solid substrate fermentation of cottonseed meal (CSM), and to determine the crude protein (CP) and amino acid (AA) content as well as the in vitro digestible CP and AA of CSM substrate fermented under optimal conditions. Six groups of autoclaved CSM substrate were incubated for 48 h after inoculation with either of the fungi Candida capsuligena ZD-1, Candida tropicalis ZD-3, Saccharomyces cerevisae ZD-5, Aspergillus terricola ZD-6, Aspergillus oryzae ZD-7, or Aspergillus niger ZD-8. One non-inoculated group was the control. Levels of initial and final FG and CP were assayed. Results indicated that microbial fermentation could greatly decrease FG levels in CSM, but it differed among species of microorganisms with C. tropicalis ZD-3 the most effective. The CSM substrate was supplemented with carbohydrate sources, urea and minerals, and one group of non-autoclaved CSM substrate was used to investigate effects of heat treatment. The treated CSM substrates were inoculated with C. tropicalis ZD-3 and incubated for 24 or 48 h. Results showed that CSM substrate supplemented with starch and sucrose enhanced detoxification of gossypol, but heat treatment and minerals were also effective in reducing FG levels during solid substrate fermentation of CSM. The detoxification effect with minerals was the best among treatments.