| Soybean hulls(SBH)are an agricultural residue produced during processing of soybeans,the contents of crude protein(CP)in SBH about 10 %,crude fiber content in SBH is 34 %.Soybean hull is widely concerned because of its high fiber and energy.Due to the high level of fiber and a variety of anti-nutritional factors(ANFs)in soybean hulls,such as urease and antigen protein,etc.,they affect the digestion,absorption and utilization of other nutrients in feed by livestock and poultry,and have a negative effect on the growth(production)performance of livestock and poultry,limit the availability of soybean hulls as livestock feed.In this study,the effect of compound bacteria fermentation was explored by selecting suitable strains for fermentation of soybean hulls;study on the optimum addition of enzymatic hydrolysis and the combination of enzymatic hydrolysis and fermentation to reduce the anti-nutritional factors in soybean hull and improve its nutritional value;finally,the optimal fermentation time was determined by bag fermentation,and the quality of fermented soybean hulls was comprehensively evaluated.Experiment 1 Screening of strains and study on fermentation of soybean hulls with compound bacteriaThe purpose of this experiment was to screen out different kinds of strains suitable for fermentation and study the fermentation effect of compound strains.Firstly,the growth performance of different types of strains from different sources was determined,and each strain of Lactobacillus,Bacillus,and yeast with better growth performance was screened out;the soybean hulls were fermented by single strain and composite strain,their fermentation characteristics were analyzed;further adding wheat bran and urea as carbon and nitrogen sources to improve the fermentation effect.The results showed that the growth performance of Lactobacillus plantarum ZR1,Bacillus natto ND1 and Saccharomyces cerevisiae ZR4 were better than other strains,so they were used as fermentation strains to ferment soybean hulls.Compared with soybean hulls fermented by a single strain,the p H of soybean hulls fermented by compound bacteria decreased,and the gas production,viable count,and lactic acid increased significantly(P < 0.05),this indicated that the soybean hulls fermented by compound bacteria were better than that fermented by single bacteria;Moreover,the addition of 10 % bran as carbon source and 1 % urea as carbon source and nitrogen source during the fermentation of the bacteria could significantly improve the fermentation effect(P < 0.05),which increased the crude protein by 22.76 %(8.83 vs 10.84 %),decreased the neutral detergent fiber(NDF)by 10.67 %(65.16 vs 54.49 %),decreased the acid detergent fiber(ADF)by 16.10 %(45.94 vs 38.54 %),and decreased the urease activity to 0.10 U/g.The degradation rate of soybean globulin reached 23.29 %,and the degradation rate of β-conglycinin reached 24.20 %.The above results showed that the nutritional value of soybean hulls could be improved by increasing the protein content and reducing the content of fiber and anti-nutritional factors in the soybean hulls fermented by the selected three strains(adding 10 % bran and 1 % urea).Experiment 2 Study on enzymatic hydrolysis of soybean hulls with fiber degrading enzyme soybean hulls and treatment of soybean hulls by combination of bacteria and enzymeDue to the high fiber content in soybean hulls,the digestion ability of monogastric animals to fiber is limited,and experiment 1,it was found that the composite fermentation of three strains of bacteria could effectively degrade anti-nutritional factors in soybean hulls.However,for the fiber content of soybean hulls itself,the composite fermentation had limited degradation ability to fibers.Therefore,this experiment aimed to study the addition amount of cellulase and xylanase to hydrolyze soybean hull fibers,and to study the effect of the combination of enzymatic hydrolysis and fermentation on soybean hulls.Firstly,through a single factor experiment,different gradient cellulase(0,100,500,and 1000 U/g)and xylanase(0,100,250,and 500 U/ g)were set up.According to the production of reducing sugar,the optimal addition amount of cellulase and xylanase was determined,and the effect of composite enzyme was determined by adding two the composite enzymes and a single enzyme.The experiment was further divided into four groups: control group(soybean hulls without strain fermentation and enzymatic hydrolysis),strain fermentation group(fermentation group,compound fermentation of Lactobacillus plantarum ZR1,Bacillus natto ND1 and Saccharomyces cerevisiae ZR4),enzymatic hydrolysis group(compound enzymatic hydrolysis of cellulase and xylanase)and enzymatic hydrolysis + fermentation group(enzyme fermentation group),Lactobacillus plantarum ZR1,Bacillus natto ND1 and Saccharomyces cerevisiae ZR4 + compound enzymatic hydrolysis of cellulase and xylanase).The results showed that when the addition of cellulase was 100 U/g and xylanase was 250U/g,the reducing sugar production was 26.21 mg/g and 25.54 mg/g,respectively(P < 0.05).Compared with a single enzymatic hydrolysis,the reducing sugar production of cellulase and xylanase compound addition reached 40.43 mg/g,which was significantly higher than that of single enzyme(P < 0.05).Compared with the fermentation group,the concentration of lactic acid and the number of viable bacteria in the fermentation group were higher,and the p H value was lower(P < 0.05).The concentration of reducing sugar in the enzymatic hydrolysis group was 45.76 mg/g,which was significantly higher than that in the control group 10.91 mg/g(P < 0.05).However,the concentration of reducing sugar in the fermentation group was 36.63 mg/g,which was lower than that in the enzymatic hydrolysis group 45.76 mg/g,(P < 0.05).Compared with the control group,the fermentation group significantly reduced the activities of urease,globulin,and β-conglycinin in soybean hulls(P< 0.05).Compared with the fermentation group,the crude protein in the bacterial enzyme fermentation group was significantly increased by 35.24 %,the true protein was increased by 35.23 %(P < 0.05),the neutral detergent fiber and acid detergent fiber were significantly decreased by 36.26 % and 39.20 %,respectively,the hemicellulose was decreased by 29.35 %(P < 0.05),the urease activity was 0.09 U/g,and the globulin and β-conglycinin were decreased by 30.23 % and 35.84 %,respectively.Compared with the enzymatic hydrolysis group,the crude protein and true protein in the bacterial enzyme fermentation group increased by 25.84 % and 25.85 %,respectively,with a significant difference(P < 0.05).The neutral detergent fiber and acid detergent fiber decreased by 30.18 % and 31.17 %,respectively,and the hemicellulose decreased by 28.14 %,with a significant difference(P <0.05).The above results showed that the combined fermentation of bacteria and enzymes could improve the nutritional value of soybean hulls.Experiment 3 Effect of bag fermentation on nutritional value and quality of soybean skin in laboratoryEnzymatic hydrolysis and fermentation can both improve the nutritional value of soybean hulls,and the combination of enzymatic hydrolysis and fermentation can greatly improve the nutritional value of soybean hulls,which is better than the effect of single enzymatic hydrolysis or single fermentation.However,the effect of enzymatic hydrolysis +fermentation in laboratory bags is not clear,and the time of bag fermentation is still to be determined.Therefore,this study aims to use this method to carry out the packaging treatment of soybean hulls in the laboratory,determine the time of packaging treatment,analyze the effects of different treatments and different fermentation time on soybean hulls,and analyze the changes in the composition and quality of soybean hulls under the optimal treatment time.Firstly,the time of bag fermentation test and its effect on soybean skin were studied,the experiment was further divided into four groups: control group(soybean hulls without strain fermentation and enzymatic hydrolysis),strain fermentation group(fermentation group,compound fermentation of Lactobacillus plantarum ZR1,Bacillus natto ND1 and Saccharomyces cerevisiae ZR4),enzymatic hydrolysis group(compound enzymatic hydrolysis of cellulase and xylanase)and enzymatic hydrolysis + fermentation group(enzyme fermentation group),Lactobacillus plantarum ZR1,Bacillus natto ND1 and Saccharomyces cerevisiae ZR4 + compound enzymatic hydrolysis of cellulase and xylanase).Samples were taken at different fermentation time points to study the optimal time of bag fermentation and evaluate the quality of the soybean hull.The results showed that the fermented soybean hulls were fragrant and yellow,and the optimal fermentation time was 5d.Under these conditions,the p H value of the bacterial enzyme fermentation group was 4.87,which was significantly lower than 5.28(P < 0.05)of the fermentation group,and the difference was significant(P < 0.05).Compared with the enzymatic hydrolysis group,the crude protein in the enzymatic fermentation group was not significantly increased(P > 0.05),the true protein was increased by 5.38 %(P < 0.05),the neutral detergent fiber and acid detergent fiber were decreased by 15.84 % and 16.99 %,respectively,and the hemicellulose was decreased by 12.80 %,with significant difference(P < 0.05).Compared with the fermentation group,the bacterial enzyme fermentation group significantly reduced the antinutritional factors in soybean hulls(P < 0.05),in which the soybean globulin decreased by32.71 %,β-conglycinin decreased by 37.06 %,and urease activity decreased to 0.1 U/g.But enzymatic hydrolysis had no significant effect on anti-nutritional factors in soybean hulls.The combination of bag fermentation and enzymatic hydrolysis could significantly improve the quality of soybean hull,and the lactic acid produced by fermentation inhibited the production of harmful bacteria such as mold,prolonged the storage period,and saved the cost to a certain extent. |
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