Study On Soybean Peptides From Fermented Soybean Meal By Mixed Strains

Soybean peptide is a mixture of small molecular peptides hydrolyzed from soybean protein. It possesses better physicochemical properties and physiologically function than soybean protein, and have broad application prospect in food, medicine and feed additives. Microbial fermentation is one of the ways to prepare soybean peptides. Combining the productions of the protease fermentation with the soybean peptide enzymolysis, this method reduced the cost and overcame the shortcoming of poor taste and bitter flavour by enzymatic hydrolysis of soybean peptides. Up to now, the microbial fermentation was considered as a more advanced and efficient method to prepare soybean peptides with a good application prospect.In this study, the purpose is to prepare soybean peptides that can be used as feed additives with peptide nutrition and health-enhancing function from industrial by-product soybean meal through the mixed microbial fermentation. First of all, Bacillus strains with better protease activity were screened, to study the in vitro probiotic properties, and then to select the strains compatibly mixed with Aspergillus oryzae to ferment soybean meal for preparing soybean peptide. By using orthogonal experiment and response surface methodology to optimize the mixed fermentation conditions and the fermentation medium respectively in order to provide references for the industrial production of soybean peptide. The results showed as follows:(1) Bacillus selection for fermented soybean meal: By using protease activity and hydrolysis degree as the indexes, the experiment investigated the fermentation capacities of various strains through the technology of liquid and solid fermentations in order to screen out some fine strains for soybean meal fermentation. Three Bacillus strains which named CS16,CS21,CS27 with the high capacity to ferment soybean meal have been screened out after preliminary and secondary screening. It laid a foundation for further study on the technology of soybean meal fermentation.(2) In vitro studies on properties of Bacillus strains as potential probiotics: The survival counts of strains were determined by imitating gastroenteric environments, the antimicrobial activities on pathogenic S.aureus,E.coli and S.typhimurium in the intestinal tract, properties of enzyme producing and the safety test of acute toxicity were also studied. The result showed in 4h, the survival rate of tested Bacillus strains was 15%～50% in gastric juice, the survival rate above 50% in the bile salt and intestinal juice. The inhibition circle to pathogens is more than 10mm in diameter, the capability of amylase and protease producing is good and test of acute toxicity LD50>20g/kgBW, could be used as a candidate for feed probiotics strains.(3) Screening for mixed fermentation and its identification Bacillus strains: Some combined strains for degradation of soybean meal were screened by means of plate mixed cultivation and actual degradation. The results showed that, the strain CS27 was obtained which can compatible with Aspergillus oryzae, identified as Bacillus subtilis.(4) Study on the fermentation by mixed strains: By using orthogonal experiment and response surface methodology to optimize the mixed fermentation conditions and the fermentation medium respectively. The results showed that under the conditions of the medium with the ratio of material to water was 1:1.149, MgSO4 was 0.048%, molasses was 0.294%, respectively, the Bacillus subtilis and Aspergillus oryzae were inoculated simultaneously under 2:1, 30℃for 48h, the content of soybean peptide in the product was 21.74% which is 5.1 times than that without fermentation treatment(3.54 %), which provides a reference for the technological expansion of soybean peptide production in industry.