| This article were conducted to study the effect of treatment sterilized by high temperature and high pressure in the solid-state fermentation on free gossypol detoxification of cottonseed meal (CSM) and solid-state fermentation on free gossypol detoxification and protein degradation on CSM by five strains of Candida spp. and two strains of Aspergillus niger solid-state fermentation, respectively.Growth curves of Candida spp. and Aspergillus niger were determined by optoelectronic turbidimetry and dry weight of mycelium method, respectively. The results showed that the terminal period of log phase of Candida spp. was occurred at 24 h of incubation at 28℃in the malt extraction liquid, and that of Aspergillus niger was happened at 24 h of incubation at 28℃in potato dextrose liquid. In order to achieve the optimal fermentation product, the seed culture fluid of Candida spp. and Aspergillus niger should be inoculated into the fermentation substrate at the terminal period of log phase of them.The control group was the material mixed with CSM, corn flour and wheat bran in the quality ratio of 7:2:1 and grinded by 60 mash screen. Exp.1 and Exp.2 were conducted to study sterilization of solid-state fermentation on free gossypol detoxification of CSM. Exp. 1 had treatment moistened in the ratio 1:0.9 of mixture to water but no sterilization, treatment autoclaved at 105℃for 20 min, treatment autoclaved at 112℃for 20 min, treatment autoclaved at 115℃for 20 min, treatment autoclaved at 121℃for 20 min. Exp. 2 had treatment moistened in the ratio 1:0.9 of mixture to water but no sterilization, treatment steam sterilized at 100℃for 30 min, treatment steam sterilized at 100℃for 60 min, treatment autoclaved at 115℃for 20 min, treatment autoclaved at 115℃for 40 min, treatment autoclaved at 121℃for 20 min. Exp. 3 was conducted to study Candida spp. and Aspergillus niger solid-state fermentation on free gossypol detoxification and protein degradation of CSM in the condition of CSM substrate autoclaved at 115℃for 40 min. Exp.3 had treatment sterilized but no inoculation, treatment inoculated C1, treatment inoculated C2, treatment inoculated C3, treatment inoculated C4, treatment inoculated C5, treatment inoculated A6, treatment inoculated A7, and treatment inoculated C1 and A6. Every sample after treated placed at the drying oven to dry at 80℃for 48 h, and grinded by 60-mash screen, then stored for determined at -20℃. The contents of free gossypol, bound gossypol and total gossypol on the CSM substrate before and after sterilization or fermentation were determined to investigate the mechanism of CSM free gossypol detoxification by microbe solid-state fermentation. The protein and peptide molecular weight distribution of CSM substrate before and after fermentation was analyzed by SDS-PAGE gel electrophoresis to investigate the degradation mechanism of CSM by solid-state fermentation, at the same time, the protein in vitro digestibility of fermented products was analyzed by dialysis tube method. Exp.1 and exp.2 showed that the detoxification rate of treat drying the CSM substrate containing water 47.37% at 80℃for 48 h was 54.57%~68.21%, and that of every treat sterilizing was above 85%, at the same time, the temperature and time of sterilization had no significant difference in the detoxification rate of CSM substrate(P>0.05). Exp. 3 showed as follow: 1)Compared with the free gossypol content of treat sterilizing that have better detoxified free gossypol, that of treats Candida spp. fermenting had no significant difference (P>0.05), and that of treats Aspergillus niger A6 and A7 fermenting increased to 211.451 mg/kg and 176.135 mg/kg from 24.739 mg/kg, respectively(P<0.01),and that of treat of mixed cultured fermentation by Candida spp. C1 and Aspergillus niger A6 was 112.244 mg/kg(P<0.01). 2)Compared with bound and total gossypol content of treat sterilizing, that of treat of microbe fermentation had no significant difference (P>0.05). 3)The solid state fermentation of three kinds of fungi all can degrade the large molecular weight(MW) protein to low molecule proteins and peptides, and especially, Aspergillus niger can degrade protein(MW=20~100 KDa) into low molecule mass(MW<14 KDa). 4)Compared with the protein in vitro digestibility of control, that of CSM substrate fermented by Aspergillus niger had a significant increase by 19.25%(P<0.05), and that of CSM substrate mixingly fermented increased by 8.18%, but they had no significant difference(P>0.05). 5)The productivity of the products fermented by Candida spp., Aspergillus niger or mixingly were 96.34±0.58%, 88.42±1.31% or 89.69±0.62%, respectively. Their crude protein contents had a very significant increase by 4.31%, 13.76% or 13.09%(P<0.01) with that of control. The crude protein contents of fermentation products had a very significant negative correlation with the fermentation productivity of products: y=97.52352-0.52748x(R2=0.9942,P<0.0001).The conclusion in this study was that: 1)The treatment by sterilization is the main function that led to the detoxification of free gossypol in CSM. 2)Aspergillus niger increased the content of free gossypol of CSM detoxified by sterilization, however, Candida spp. can detoxify the free gossypol of CSM, but both cann't degrade the gossypol. 3)Solid-state fermentation of CSM by Aspergillus niger possessed a stronger capability of protein degradation as a result is that the large molecular weight can be degraded to proteins or peptides with MW less than 14 KDa. 4)Aspergillus niger solid-state fermentation can significantly increase the protein in vitro digestibility of CSM substrate. 5)The fermentation could decrease the content of dry matter and increase the content of crude protein of fermented product, and the crude protein contents of fermented products and fermentation productivity had significantly a negative correlation.
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