| Sea buckthorn polyphenols are abundant and diverse,but their forms are difficult to be absorbed by the human body.The β-glucosidase of lactic acid bacteria(LAB)can effectively convert polyphenols from glycosides with large molecular weight and poor permeability to small-molecule aglycones that are easily absorbed by the human body.Therefore,it is important to fully understand the changes of polyphenols during the fermentation of sea buckthorn by LAB and to determine the interaction between the β-glucosidase of LAB and sea buckthorn polyphenols to improve the bioavailability of polyphenols.This topic explored the microbial structure and bacterial diversity of jiangshui in Ningxia,and isolated the dominant LAB with high production of β-glucosidase and strong acid resistance for the fermentation of sea buckthorn juice.The biochemical properties of sea buckthorn juice at different fermentation stages were explored through the best fermentation process.The changes of total phenols in fermented sea buckthorn juice,the differences of various polyphenol metabolites and the metabolic pathways involved in polyphenol differential metabolites were studied.An interrelated response model was established for β-glucosidase activity of LAB and key polyphenol differential metabolites.The results of this topic provide a considerable theoretical basis for the relationship between the β-glucosidase of LAB and the action of sea buckthorn polyphenols,and also provide a certain scientific reference for the related research on improving the utilization rate of sea buckthorn polyphenols.The specific research is as follows:1.The MIDI microbial identification system combined with Illumina Novaseq technology to analyze the microbial structure and bacterial diversity in jiangshui of Ningxia.The results showed that the proportion of bacteria in jiangshui was the highest,and the content of Gram-positive bacteria was higher than that of Gram-negative bacteria.The second was fungi,while actinomycetes,AM fungi,and eukaryotes accounted for a very low proportion.Firmicutes and Proteobacteria were the dominant bacterial phyla,and Lactobacillus was the dominant bacterial genus.The proportion of opportunistic pathogens was small.The bacterial communities of samples from different regions and different fermentation times were not significantly different(P>0.05).2.LAB from Ningxia were isolated and the LAB with high β-glucosidase production were screened for sea buckthorn juice fermentation.254 strains of LAB were isolated from jiangshui in Ningxia by pure culture method.Among them,181 strains of LAB were high yield of β-glucosidase,and a total of 4 strains were obtained by further acid resistance experiments:YHG1-155,YHG2-137 and WHL1-2 were the Lactobacillus plantarum and YHG2-154 was the Lactobacillus fermentum.After comprehensive comparison of the above data,YHG 1-155 was selected for subsequent fermentation experiments.3.Taking sensory evaluation as the index,the process of YHG 1-155 fermentation sea buckthorn juice was optimized by single factor experiment,Plackett-Burman experimental design and response surface optimization experiment.The optimal fermentation conditions were as follows:fermentation time of 10 days,ratio of material to water of 1:4,fermentation temperature of 30.0℃,inoculation amount of 3.0%and sugar addition amount of 6.0%.Under this fermentation process,YHG1-155 could always maintain high vitality,pH value did not change significantly(2.79-2.90),organic acid content change trend was different,and antioxidant index increased compared with before fermentation.4.Studied on the relationship between the β-glucosidase of LAB and the transformation of fermented sea buckthorn polyphenols.The metabolic changes of phenolic compounds in sea buckthorn juice fermented by LAB were studied by Folin-Ciocalteau method and UPLC-MS/MS technology.The results showed that the total phenolic content of sea buckthorn changed significantly before and after fermentation.The changes of phenolic metabolites in different fermentation stages were extremely complex,among which the differential metabolites of phenolic acids and flavonoids were dominant in seabuckthorn polyphenols,while the differential metabolites of tannins,lignans and coumarins,and stilbene were less.The changes of phenolic acid,flavonoid and tannin metabolites were most significant at 0 d-2 d,2 d-4 d and 4 d-8 d,respectively.The metabolic pathway,phenylpropane metabolites and flavonoid and flavonol biosynthesis pathways were significantly enriched in the process of polyphenol metabolism of seabuckthorn(P<0.005).The change trend of β-glucosidase activity of LAB during fermentation was determined by p-NPG method.The results showed that the enzyme activity was closely related to the change of YHG1-155.Principal component analysis was used to analyze the correlation between 10 key polyphenol metabolites and β-glucosidase activity,and the response model for the β-glucosidase activity of YHG1-155 and key metabolites of polyphenols was established:F=0.649X4-0.377X20+0.525X33(F:β-glucosidase activity of YHG1-155,X4,X20 and X33 represent the contents of 2-Phenylethanol,Apigenin and Vitexin-2"-O-glucoside,respectively.)... |
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