Screening Of Aroma-Producing Microbe For Traditio Nal Fermented Pepper And Research Of Its Aroma-Pr Oducing Mechanism

Traditional fermented pepper is a specialty of Hunan.It is one of the main seasonings of Hunan cuisine.The rich microbial species create the characteristic of fermented pepper sauce with strong flavor.However,the traditional fermented pepper has a long fermentation cycle,unstable quality,and the molecular mechanism of microbial co fermentation and aroma production still not clear.Based on the early analysis of microbial diversity in different fermentation stages of naturally fermented peppers,this study separated the advantages and aroma-producing microorganisms in different fermentation stages of naturally fermented peppers,and provided strains for the development of vegetable complex starter;Using RNA-seq technology to study the molecular mechanism of co-enzymatic and fragrance generation of superior,aroma-producing microorganisms,revealing the molecular mechanism of co-enzymatic and fragrance generation of superior,aroma-producing microorganisms from the transcriptome level;The changes of volatile flavors of inoculated and naturally fermented peppers were analyzed and compared,and the metabolomic level confirmed the excellent aromatizing performance of the selected fermenting microorganisms and the good inheritance of naturally fermented peppers.The main research results are as follows:1.Breeding research results of aroma-producing microorganisms in traditional fermented peppers486 strains of suspected lactic acid bacteria were isolated and purified from traditional fermented chili peppers.Through inoculation and fermentation,three excellent strains with excellent aroma production were selected using sensory score and acetoin content as aroma evaluation indexes.H3 D was identified as Lactobacillus plantarum,6-12 as Lactococcus pentosus and 6d-16 as Lactobacillus pentosus.The contents of acetoin in the fermentation broth of the three strains of lactic acid bacteria in 24 hours were 36.272,55.413 and 28.365mg/L.And the three strains of lactic acid bacteria have the characteristics of fast acid production,acid resistance,salt resistance and bile salt resistance,and are suitable for inoculating fermented pepper strains.2.Study on metabolic pathway of key flavor substances of fragrance-producing strainsAccording to the analysis of RNA-seq,1929 differentially expressed genes were screened from Lactobacillus plantarum H3 D under starvation stress and normal culture conditions,958 genes were up-regulated and 971 genes were down regulated.Pediococcus pentosus 6-12 screened 1177 differential genes,591 genes were up-regulated and 586 genes were down-regulated.Screening of Lactobacillus pentosus 6d-16 resulted in 1622 differential genes,839 genes were up-regulated and 783 genes were down-regulated.The differences of phosphotransferase system,glycolysis pathway,pyruvate metabolism,fatty acid synthesis and acetoin metabolism related to carbon metabolism in the fermentation process of three strains of lactic acid bacteria were analyzed.The related pathways,regulatory enzymes and differential expression of coding genes in the synthesis and metabolism of acetic acid,lactic acid,acetoin,diacetyl,2,3-butanediol and fatty acid of three strains of lactic acid bacteria were explored.3.Study on the Change of Volatile Flavor Substances During Fermentation of Inoculated Fermented Pepper and Naturally Fermented PepperInoculating lactobacillus can shorten the fermentation time of Capsicum.The fermentation time is 10 days for the p H of Capsicum to reach 4.5 and the total acid to reach0.5g/100 g,but 20 days for the natural fermentation capsicum.Using HS-SPME-GC-MS,a total of 203 kinds of volatile substances in each fermentation stage of naturally fermented pepper were detected,and the most abundant flavor substances were found on the 20 th day of fermentation(108 kinds).Among the 4 kinds of inoculated fermented peppers,181 kinds of volatile flavors were detected by inoculation of mixed strains.The 10 th day(107kinds)flavors of fermentation were the most abundant,which were close to the 20 th day(108kinds)of naturally fermented peppers.There are 131 substances in common,which is the highest in all inoculated fermentation samples,and has certain inheritance to the good flavor of naturally fermented pepper.Inoculated with Lactobacillus pentosus 6d-16 fermented peppers,a total of 151 flavor substances were detected,which were not as abundant as natural fermentation.The content of aldehyde and other aldehydes compounds in fermented peppers inoculated with Lactobacillus plantarum H3 D is higher than that of naturally fermented peppers in the same period.The inoculation of Pediococcus pentosaceae 6-12 fermented peppers has more types and higher contents of ketone compounds than natural fermented peppers.Fermented chili adds flavor.Two inoculation methods can add flavor to fermented peppers.