| Object:This dissertation was to study the effect of different treatments on the contents of total gossypol (TG), free gossypol (FG) and bound gossypol (BG) in cottonseed cake (SCC) and its mixed substrates, and the reduction regularity of different types of gossypol, and then to explore the elimination mechanism of FG in CSC during solid-state fermentation.Methods:The dissertation consists of three experiments. The method of Experiment 1 was that the design of orthogonal experiment was carried out in this experiment from 3 factors and 3 levels which included the heating time (10 min,20 min or 30 min), heating temperature (100℃,110℃or 120℃) and humidity of CSC (40%,50%or 60%). There were 9 treatments in all according to the orthogonal table L9 (34). The method of Experiment 2 was that different treatments of CSC and its mixed substrates were fermented by C. tropicalis ZD-3, and then to determine the content of TG, FG and BG in fermented products, so as to explore the detoxification mechanism of microbial fermentation of CSC through the reduction regularity of various gossypol. The method of Experiment 3 was that CSC mixed substrates were fermented by mixed culture of different proportion of C. tropicalis ZD-3 with S. cerevisiae ZD-5, or C. tropicalis ZD-3 with A. niger ZD-8, and then through determining the content of TG, FG and BG in fermented products to explore the detoxification mechanism of microbial fermentation of CSC.Results:The results of Experiment 1 showed that the heating time, heating temperature and humidity of CSC all had extremely significant effects (P＜0.01) on the reduction of TG, FG and BG in CSC during heat treatment, as for FG the main effect factor was humidity of CSC, next being the heating time and last heating temperature, while for TG and BG, the main effect factor was heating temperature, next being the heating time and last humidity of CSC.There were extremely significant interaction effects (P<0.01) on the reduction of TG, FG and BG in CSC among the 3 factors, and the group of A3B3C2, that is to say, the treatment of heating time 30min, heating temperature 120℃and humidity of CSC 50%, was the best. During the heating process, the FG decrease mainly depended on the interaction of the heating time, temperature and humidity of CSC, and FG of reduction part was degraded completely, not changed into BG, therefore, the objective of CSC detoxification was accomplished. The results of Experiment 2 showed that under the condition of substrates being heated or not, the fermentation made the most of FG and BG degraded, rather than being formed into BG, and the amount of TG degradation was equal to that of FG and BG elimination, while the addition of FeSO4 in substrates could promote the degradation of FG and BG in the fermented products of CSC and its mixed substrates. The difference between two treatments was that the amounts of TG, FG and BG degradation of unheated substrate fermentation were smaller than that of heated substrate fermentation.The results of Experiment 3 showed that after CSC mixed substrates were fermented by mixed culture of different proportion of C. tropicalis ZD-3 with S. cerevisiae ZD-5, or C. tropicalis ZD-3 with A. niger ZD-8, the content of TG, FG and BG in the substrates were all extremely reduced (P<0.01), and the reduction parts were all decomposed. Between two kinds of mixed culture, the fermentation efficiency of C. tropicalis ZD-3 with S. cerevisiae ZD-5 was superior to that of C. tropicalis ZD-3 with A. niger ZD-8. Effects of the proportion between yeasts inocula on fermentation efficiency was significant (P<0.01), and when the ratio of C. tropicalis ZD-3 with S. cerevisiae ZD-5 was 3 to 1, the detoxification efficiency was the best, detoxification rate reaching up to 90.82%.Conclusion:(1)The heating time, heating temperature and humidity of CSC all had extremely significant effects on the reduction of TG, FG and BG in CSC during heat treatment, and the FG decrease mainly depended on the interaction of heating time, temperature and humidity of CSC, and FG of reduction part was degraded completely, not changed into BG. (2) The fermentation could make most of FG and BG degraded, rather than being formed into BG, and the amount of TG degradation was equal to that of FG and BG eliminated together, while the addition of FeSO4 in substrates could promote the degradation of FG and BG in the substrates. (3) Mixed culture fermentation by C. tropicalis ZD-3 with S. cerevisiae ZD-5, or C. tropicalis ZD-3 with A. niger ZD-8, could extremely reduced the contents of TG, FG and BG in the substrates, and the FG and BG of reduction parts were all decomposed. In addition, the fermentation efficiency of C. tropicalis ZD-3 with S. cerevisiae ZD-5 was superior to that of C. tropicalis ZD-3 with A. niger ZD-8. |
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