Study On Screening Of Yeast On Degradation Efficiency Of Gossypol And Its Fermentation Process

The toxic substances in the presence of gossypol cottonseed greatly restrain the application of cottonseed meal in animal feed industry, through microbial solid fermentation to degrade the gossypol of cottonseed meal.Several gossypol-degradation yeast probiotic strains were isolated in this study. After determined their degradation ability, the best strain were selected for feed fermentation.A total of 33 strains yeast were isolated from peels,by the 26 S rDNA D1 / D2 region sequence analysis has carried on the classification and identification, identification results:Candida tropicalis(9 strains), Kluyveromyces marxianus(2 strains), Pichia kudriavzevii(6 strains),Pichia jadinii(1 strain),Meyerozyma guilliermondii(2 strains),Candida rugosa(2 strains),Candida mesorugosa(2 strains),Candida orthopsilosis(2 strains)and 7 unclassified strains.These new isolated strains coupled with other 87 yeast strain were inoculated into the solid medium with gossypol acetate as the sole carbon source to evaluate their gossypol acetate-degradation ability. The results demonstrated that Issatchenkia orientalis and Kurdish Pichia pastoris grow well, and a slower growth rate was observed for Candida utilis. To confirm their acetate-degradation ability, 1 or 2 strains were selected in each species, and inoculated into the liquid medium with gossypol acetate as the sole carbon source. Two strains Pichia kudriavzevii SD2 A and C. utilis SH87 yiled high biomass. As a result, further experiments were carried out for these two strains to utilized in cottonseed fermentation.The cottonseed meal by solid-state fermentation of raw materials, the rate through the comparison of different fermentation conditions under SD2 A SH87 gossypol degradation.The results showed that the best treatment conditions for SH87 were as follws: fementation time 36 h, moisture 42%, temperature 30℃; while that of SD2 A were 10 percent of inoculation amount, pH 6.0, moisture 42%, and temperature 37℃. After 36 h fermentation, 83.42% gossypol was degrated. During the mixed fermentation process, increasing the proportion of yeast amount improved the gossypol degradation rate. It indicate that the degradation of gossypol was mainly caused by the yeast strains.SH87 was chosed to prepare solid agents. In order to improve the production of active cells, the optimum conditions for solid state fermentation medium were studied. The best treatment conditions were as follows: fermented with box 2 d, solid state fermentation medium moisture 45%, dried to a finished fermented material at 13% moisture at 45 ℃; the ative cell numbers achieved 6.13×108 cfu·g-1.The degradation ability of SD2 A was improved by UV mutagenesis experiments. Compared with the wild-type strain, the mutant strain resulted in a 10.71% increase in gossypol degradation, which achived 93.95%. Cottonseed meal for solid-state fermentation strain SH87 amplification experiments 44 h after fermentation, the crude protein content increased by 7.25%, the degradation rate of gossypol was 87.02%.To determine the location of gossypol dgradation enzymes, the proteins were extracted and purified fron the liquid medium that cultured SD2 A, and then mixed with gossypol acetate at 37 ℃ for different hours. A sharp decrease of gossypol degradation was observed in the mixture. Which demonstrated that the extracellular enzymes play an important role in gossypol degradation. Replace liquid fermentation medium with glucose as the sole carbon source gossypol acetate material after extraction of gossypol acetate also degradation; guess this extracellular enzyme is not inducible.