不同发酵水分及菌酶协同发酵对豆粕品质的影响

[目的]探讨不同发酵水分及菌酶协同发酵对豆粕品质的影响。[方法]①采用单因素试验设计,设置5个不同水分处理组,料水比分别为1∶0.4、1∶0.5、1∶0.6、1∶0.7、1∶0.8,每个处理组3个重复;使用复合益生菌（枯草芽孢杆菌∶酵母菌∶粪肠球菌=1∶1∶1）发酵豆粕,通过测定分析发酵豆粕表观特征、营养指标及活菌含量,确定最适料水比。②采用单因素试验设计,设置5个不同中性蛋白酶添加量处理组,添加量分别为0、100、200、400、800 IU/g,每个处理组3个重复,进一步测定发酵豆粕表观特征、营养指标、活菌含量及蛋白质亚基分布,确定最佳中性蛋白酶添加量。[结果]①不同料水比条件下,各处理组发酵豆粕粗蛋白水平无显著（P=0.074）差异,料水比为1∶0.6时粗蛋白含量最高,较发酵前提高了9.39%;随着初始发酵水分的提高,发酵豆粕pH值极显著（P<0.01）降低,乳酸含量及3种菌的存活量极显著（P<0.01）升高,1∶0.6组发酵后乳酸含量显著（P<0.05）高于1∶0.4组和1∶0.5组;复合菌的存活量在料水比为1∶0.8时最高,总量达到1.43×10⁹ CFU/g。结合上述试验结果并考虑工业化生产条件,选择料水比为1∶0.6作为最适发酵水分开展后续试验。②在料水比为1∶0.6条件下,不同蛋白酶添加水平对各组发酵豆粕粗蛋白含量的影响不显著（P>0.05）,但随着蛋白酶添加量的增加,小分子蛋白水平线性提升,在蛋白酶添加量为800 IU/g的处理组中,<30 kDa范围内的蛋白质水平高达65.56%,较未添加组小分子蛋白质含量提高2.61倍;发酵豆粕中3种菌的存活量随着蛋白酶添加量的增加而降低,100 IU/g处理组枯草芽孢杆菌和粪肠球菌的存活量极显著（P<0.01）高于200、400、800 IU/g处理组,酵母菌的存活量极显著（P<0.01）高于400、800 IU/g处理组。[结论]选择料水比为1∶0.6并在底物中添加100 IU/g的中性蛋白酶协同发酵可有效改善豆粕的品质。

Effects of Initial Water Content and Co-fermentation with Probiotics and Protease on Quality of Soybean Meal

[Objective] This experiment was conducted to explore the effects of different initial water contents and co-fermentation with probiotics and protease on quality of soybean meal. [Method] ① A single factor experimental design was adopted to determine the optimal ratio of fermentation material to initial water. Five treatment groups with different initial water contents were set up, and the ratios of material to water were 1∶0.4, 1∶0.5, 1∶0.6, 1∶0.7 and 1∶0.8, respectively. There were three replicates for each treatment group. The compound probiotics （Bacillus subtilis∶yeast∶Enterococcus faecalis=1∶1∶1） were used as starter to ferment soybean meal, and the apparent characteristics, nutritional indicators and living bacteria contents of the fermented soybean meal were assessed. ②A single factor experimental design was used to set up five treatment groups with different neutral protease addition amount of 0, 100, 200, 400 and 800 IU/g. Each treatment group had three replicates. The apparent characteristics, nutritional indicators, live bacteria contents, and protein subunit distribution of the fermented soybean meal were further analyzed to determine the optimal neutral protease addition amount. [Result] ①There was no significant （P=0.074） difference in crude protein level of the fermented soybean meal with varied ratios of material to water. The highest crude protein level of the fermentation product was observed when the ratio of material to water was 1∶0.6, which was elevated by 9.39% compared with the soybean meal before fermentation. With the increase of initial water content of the fermentation system, the pH value of fermented soybean meal was decreased significantly （P<0.01）, while the content of lactic acid and the survival amount of the three species of microbes in the compound probiotics were elevated significantly （P<0.01）. The content of lactic acid after fermentation in 1∶0.6 treatment group was significantly （P<0.05） higher than that in 1∶0.4 and 1∶0.5 treatment groups. The survival amount of the three species of microbes in the compound probiotics was the highest when the ratio of material to water was 1∶0.8, with the total amount reached 1.43×10⁹ CFU/g. Considering the industrial production conditions with the above results, the optimal ratio of material to water for the subsequent experiment was determined as 1∶0.6.②With the ratio of material to water at 1∶0.6, different protease addition levels had no significant （P>0.05） effect on the crude protein content of fermented soybean meal. However with the increase of protease addition amount, the proportion of small molecular proteins in fermentation product increased linearly. In the treatment group with protease addition of 800 IU/g, the proportion of proteins with molecular weights less than 30 kDa was as high as 65.56%, which was 2.61 times higher than that in the group without protease addition. The survival amount of the three species of microbes in the compound probiotics was decreased with the increase of protease addition amount. The survival amount of Bacillus subtilis and Enterococcus faecalis in 100 IU/g treatment group was extremely significantly （P<0.01） higher than that in 200, 400 and 800 IU/g treatment groups, and that of yeast was extremely significantly （P<0.01） higher in comparison to 400 and 800 IU/g treatment groups. [Conclusion] The quality of soybean meal can be effectively improved by a co-fermentation with addition of compound probiotics and 100 IU/g neutral protease in the substrates at a ratio of material to water of 1∶0.6.