The Mechanism Study Of Improving Quality Of Mixed Solid-state Fermentation Of Soybean Meal

Solid-state fermentation of soybean meal was widely recognized to degrade anti-nutritional factors and improve protein utilization. However, the quality of fermented products from different manufacturers had much difference, and the same manufacturer’s product quality was not stable in the mass production. The difference of strain, fermentation equipment and fermentation conditions can cause these results. Part of the mechanism of solid-state fermentation was not clear also important factors. In this study combined with the distribution of the growth of microorganisms during fermentation, the physical properties of different particle size of soybean meal were analyzed. According to a series of indicators measured in the fermentation process to find the key factors to enhance the quality of fermented soybean meal.The proportion of different size presented normal distribution. The particle size of each meal of 16-20 mesh、20-40 mesh accounted for 22%. 4-8 mesh accounted for 8%, the following of 80 mesh was 3%. The meal of porosity was the lowest by 20-40 mesh of 55.36%. Soybean meal porosity below 80 mesh particle size was a maximum of 61.96%. The specific surface area of particles decreased with increasing particle size. Porosity and specific surface area of joint decision fermenting bacteria’s growth and development. So choosing the right balance was the key point.The experimental use of Bacillus subtilis, lactic acid bacteria, yeast as the fermentation bacteria, the Bacillus subtilis grow best in 12 h after the growth rate decreases; lactic acid bacteria and yeasts was in 36 h too, after the growth rate drop; wherein Bacillus subtilis, yeast secondary growth was observed at 48-60 h. In this experiment, the key points was 12 h of fermentation, which can select ventilation stir measures at this time.Adverse oligosaccharides complete degradation in 15 h,and soluble sugar keep stabilize in 36 h; alkaline protease accumulated along with fermentation, prompting rising p H; the crude protein and acid-soluble peptide content all peaked at 48 h. The fermentation time required more than 36 h according to the bacterial growth, and the fermentation time can not exceed 60 h according the viscosity changes of the fermentation。So under the experimental conditions, the optimal fermentation time was 48 h.The phenomenon of clamminess in solid-state fermentation of soybean meal is bound to exist, mainly due to sticky was the increased of protein and small molecule peptide, but too sticky meal will slow the rate of drying, increase the crushing energy consumption. According to the relationship between viscosity(y) and fermentation time(x) can be fitted equation: log y = 0.0134 x + 0.7773.The quality of the fermented soybean meal was completely in line with the standard of the agricultural department under the condition of this experiment, but it should also be based on the time point of the maximum number of aerobic bacteria flora appears, hold the balance between porosity and surface area, crude protein and soluble sugar content, acid-soluble peptides and viscosity to improve the quality of fermented soybean meal.