Effects of multiple strains fermentation and enzymatic hydrolysis on nutrient composition and quality of soybean hulls

Abstract:

[Background] Soybean hulls as a crude feed have high digestibility, but their fiber content is high, and contains a variety of anti-nutritional factors such as urease and antigen protein, which limits its application in monogastric animal feed. [Objective] The aims of this study to reduce the content of fiber and anti-nutritional factors in soybean hulls by combination of bacteria fermentation and enzymatic hydrolysis. The packaging treatment of soybean hulls by using this method was conducted in the laboratory to evaluate the number of molds and the nutritional value and quality of soybean hulls for the foundation of future industrial application of soybean hulls. [Methods] The experiment was divided into four groups:control group (soybean hulls without fermentation and enzymatic hydrolysis group), strain fermentation group (Lactobacillus, Bacillus, and Saccharomyces mixture fermentation), enzymatic hydrolysis group (cellulase and xylanase enzymatic hydrolysis), and enzymatic hydrolysis + strain fermentation group (Lactobacillus, Bacillus and Saccharomyces compound fermentation + cellulase and xylanase enzymatic hydrolysis). The optimal time for packaging treatment was selected. [Results] Compared with the control group, the pH value, reducing sugar content, urease activity, globulin, and β-conglycinin of the fermentation group were decreased (P<0.05). The reducing sugar, crude protein, and true protein content in the enzymatic hydrolysis group was increased (P<0.05), while the neutral detergent fiber and acid detergent fiber were decreased (P<0.05). The pH value, the contents of neutral detergent fiber, and acid detergent fiber were decreased (P<0.05), while the reducing sugar content, crude protein, and true protein contents were increased (P<0.05) in the bacteria fermentation and enzymatic hydrolysis group. Compared with the fermentation group, lactic acid concentration, and viable bacteria number were higher, while pH value, urease activity, globulin, and β-conglycinin were decreased in the bacteria fermentation and enzymatic hydrolysis group (P<0.05). Compared with the enzyme hydrolysis group, the reducing sugar concentration, the neutral detergent fiber, acid detergent fiber, and hemicellulose in the bacteria fermentation and enzymatic hydrolysis group were decreased (P<0.05). In the bag experiment, the pH value of the enzyme fermentation group was 4.87 at the optimal fermentation time of 5 d, which was lower than that of the other groups (P<0.05). Compared with the fermentation group, the reducing sugar content, crude protein, and true protein in the bacteria fermentation and enzymatic hydrolysis group were increased (P<0.05), while the urease activity, globulin, β-conglycinin, neutral detergent fiber, acid detergent fiber and, hemicellulose in the bacteria fermentation and enzymatic hydrolysis group were decreased (P<0.05). Compared with the enzymatic hydrolysis group, the reducing sugar content, neutral detergent fiber, acid detergent fiber and, hemicellulose in the bacteria fermentation and enzymatic hydrolysis group were decreased (P<0.05). The content of mold in the bacterial enzyme fermentation group was only 0.89 lg(CFU/mL), which was lower than that in the other groups (P<0.05). [Conclusion] The combination of bacteria and enzymes can increase the crude protein and true protein content, reduce the content of fiber and anti-nutritional factors, inhibit the production of mold in soybean hulls, and finally improve the nutritional value and quality of soybean hulls.

Key words:cellulase;xylanase;anti-nutritional factors;microbial fermentation;combination of bacteria and enzyme;bag experiment;nutritional value