In order to improve the utilization rate of the milk thistle residue, this study used the synergistic fermentation of multiple strains and proteases to increase the small peptide content of the fermented feed produced by the milk thistle residue. Taking the small peptide content of the milk thistle residue fermented feed as an indicator, the optimal fermentation process was obtained by single-factor optimization experiments and the response surface methodology. The optimal fermentation process was as follows: fermentation time of 7 days, inoculum size of 15%, inoculation ratio of aerobic strains: anaerobic strains = 1: 2, solid-state fermentation water content of 66%, fermentation temperature of 36℃, and amount of protease was 0.25% acid protease+0.25% bromelain. Under the above process, the small peptide content of the fermented feed from milk thistle residue was greatly improved to 57.86%. These results inferred that the added proteases were beneficial to the growth of fermentative microorganisms, the secretion of protease and the increase of the small peptide content.
During the fermentation of corn stalk bio-feed, the quantity of bacteria in corn stalk bio-feed was counted by fluorescence quantitative PCR and plate colony counting respectively. The comparative analysis of these studies was used to explore the feasibility of fluorescence quantification methods and changes in microbiota during fermentation. The results showed that the standard deviation of fluorescence quantitative method was smaller than that of plate method, but the trend was similar. The biomass of Bacillus subtilis, Lactobacillus plantarum and Saccharomyces cerevisiae reached their maximum on the third, fifth and fifth day respectively, and then decreased gradually and maintained at a certain level. The experiment showed that the fluorescence quantitative PCR method can accurately quantify the number of bacteria in corn stalk bio-feed, and it is a better method to quantitatively detect the dynamic changes of different kinds of bacteria in corn stalk bio-feed.
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