Study On Breeding Of Strains For Gossypol Reducing And Optimizing Of Culture Parameters

China is one of the highest yield of cottonseed meal(about 4~6 million tons every year) countries in the world. As a protein resource, only a little of cottonseed meal was used in feed industry due to the presence of toxin, gossypol.To obtain strains for gossypol detoxification, 16 soild samples were collected and 144 wild strains were isolated. Among them, a strain(Y-2) possessed the highest initial detoxification(45%). The strain Y-2 was identified as Pichia guilliermondii by traditional and molecular genetic identification. This strain was non-pathogenic yeast, and was first reported used on degredation of gossypol. Mutant YUV-51 with the highest detoxification was obtained by UV mutation. The detoxification rate was up to 55%. Mutant YUV-51 had stable detoxification by continuously cultivating 12 generations.Single factor experiment was used to confirm optimum conditions. Based on the results, the optimum fermentation conditions of cottonseed meal under help of the Pichia guilliermondii were confirmed, respectively.The marked impact of Pichia guilliermondii fermentation factors were confirmed as follows: temperature, wheat bran adding, and the ratio of substrate to water. The optimum fermentation conditions of detoxification were confirmed using Design Expert. The results show that detoxification was up to 62% under the optimum fermentation conditions: incubation temperature at 31.7°C, 16.3% wheat bran in substrate, initial moisture content of solid substrate 50.9%.Heat-moisture treatment was used to check gossypol's stability, the higher the temperature and moisture, the lower the gossypol content. The free-gossypol's decrement was lower than total-gossypol, so most probably, the gossypol was degradated by yeast instead of being transformed into the bound-gossypol. In liquid state fermentation, gossypol(molecular weight 518) decreased and new material(molecular weight 499) appeared, one material(molecular weight 477) increased remarkably, this two matters maybe the intermediate metabolite of gossypol.In the end, the content of nutrient composition in the meal was determined under optimum condition. It demonstrated that the content of protein increased 5%, amino acid increased 5.08%, the total sugar decreased 5.5%.