固态发酵对棉籽粕棉酚脱毒及蛋白降解的影响

Effect of solid-state fermentation on gossypol detoxification and protein degradation in cottonseed meal

【目的】研究采用假丝酵母（Candidaspp．）和黑曲霉（Aspergillusniger）对棉籽粕进行固态发酵后，棉籽粕中棉酚含量的变化及其中蛋白的降解规律。【方法】利用5株假丝酵母和2株黑曲霉，分别对棉籽粕进行单菌种及复合菌种固态发酵，试验设灭菌不接种组（灭菌组），灭菌分别接假丝酵母c1、c2、c3、c4、c5和黑曲霉A6、A7菌组，及灭菌接C1和A6复合菌组，共9个处理组和1个对照组，比较固态发酵前后棉籽粕底物中游离棉酚（FG）和结合棉酚（BG）的含量，采用SDS-PAGE凝胶电泳分析发酵前后棉籽粕底物中蛋白质和小分子肽分子质量的分布范围。【结果】（1）在高温高压灭菌处理对棉籽粕底物中大部分FG已脱毒的情况下，5株假丝酵母发酵组与灭菌处理组FG含量差异不显著，2株黑曲霉发酵组不但没有脱毒作用，反而使FG含量从灭菌处理组的24．739mg／kg分别增加到211．451和176．135mg／kg，假丝酵母和黑曲霉复合发酵组FG含量介于二者之间；（2）在灭菌处理已极显著降低（P〈0．01）棉籽粕底物BG和总棉酚（TG）含量的情况下，各菌株发酵对BG和TG的含量影响差异不显著（P〉0．05）；（3）假丝酵母及黑曲霉固态发酵均能将棉籽粕底物中分子质量在20～100ku的大分子蛋白降解为小分子蛋白和小分子肽，其中黑曲霉可将蛋白质降解为14ku以下的小分子蛋白和小分子肽。【结论】（1）微生物固态发酵能使棉籽粕棉酚脱毒主要是高温高压灭菌的作用；（2）假丝酵母对棉籽粕中游离棉酚有一定的脱毒作用，而黑曲霉增加了游离棉酚含量，二者对棉酚均无明显降解作用；（3）黑曲霉固态发酵棉籽粕具有较强的蛋白降解能力，可将高分子质量的棉籽蛋白降解为14ku以下的小分子蛋白和小分子肽。

[Objective]The gossypol detoxification and protein degradation by solid-state fermentation of Candida spp. and Aspergillus niger on cottonseed meal （CSM） were investigated in this experiment. [Method] Five strains of Candida spp. and two strains of Aspergillus niger were cultured singly or mixingly by solid-state fermentation methods,and the experiment was allotted into one control and nine treat- ment groups,including sterilized but no inoculation, sterilized and inoculated Candida spp. C1, C2, C3, C4, C5,and Aspergillus niger A6, AT, respectively, and mixingly inoculated C1 and A6 group. The contents of free gossypol （FG） and bound gossypol （BG） in CSM before and after fermentation were de.termined. At the same time, the distribution of protein and peptide molecular weight was also analyzed by the SDSPAGE gel electrophoresis. [Result] （1）Under the conditions that free gossypol was detoxified mostly by sterilizing with heating and high pressure,there was no significant difference of FG contents when fermen- ted by five strains of Candida spp. after sterilizing,while that of Aspergillus niger A6 and A7 fermenta- tion increased to 211. 451 and 176. 135 mg/kg from sterilizing 24. 739 mg/kg respectively, and that of mixed fermentation by Candida spp. C1 and Aspergillus niger A6 was moderate compared with that of two microbe fermentations above. （2）Under the conditions that bound and total gossypol contents in CSM significantly decreased by the sterilizing treatment （P〈0.01）, the effect of microbe fermentation on BG and TG contents had no significant difference （P〈0.05）. （3）All the solid-state fermentation of fungi se- lected in this paper can degrade the proteins with large molecular weight （MW=20-100 ku） to those with small molecular weight proteins and peptides, especially, the MW of protein can be degraded to 14 ku or less when fermented by Aspergillus niger. [Conclusion] （1）The treatment by sterilization was the main function leading to the detoxification of free gossypol in CSM. （2）Aspergillus niger increased the contents 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 pos- sessed a stronger capability of protein degradation as a result of that the large molecular weight can be degraded to proteins or peptides with MW less than 14 ku.