Fermentation Relationship Between Microorganism And Flavor Formation In Traditional Aspergillus-type Douchi

As one of the traditional Douchi in China,Aspergillus Douchi is a kind of flavoring non-staple food with the same origin of medicine and food,and the flavor of Douchi is one of the key factors to determine its quality.However,the traditional extensive production method of Aspergillus type Douchi is difficult to ensure the stability of Douchi quality,and there is a big food safety risk.Therefore,before the industrial production of good flavor Douchi,we should first form a comprehensive understanding of the flavor characteristics and flora distribution of Aspergillus type Douchi under the traditional technology,but the understanding of its law in the past is still not very deep.Therefore,the microbial community composition of traditional Aspergillus Douchi was analyzed by microbial culturability,16 S r RNA sequencing and macro gene shotgun sequencing;The basic quality and flavor components(volatile flavor compounds,free amino acids)of traditional Aspergillus Douchi were determined,and the physicochemical characteristics of Douchi were evaluated.Based on the above research data,the relationship between microorganisms and flavor formation in traditional Aspergillus Douchi was discussed,and the flavor differences between culturable microorganisms and traditional Aspergillus Douchi were compared.The process and results are as follows:In terms of traditional Aspergillus Douchi,the abundance of culturable microorganisms showed a downward trend.Among the 18 microorganisms isolated,the dominant microorganisms were bacteria,including Bacillus velezensis,Bacillus licheniformis,Staphylococcus gallinarum,Staphylococcus saprophyticus and Pediococcus acidilactici.The results showed that Staphylococcus was the only dominant genus in the whole process of post fermentation,and the average relative abundance was about 50%;The lactic acid bacteria represented by weissella,Pediococcus and lactobacillus were mainly distributed in the initial stage of post fermentation.The relative abundance of Bacillus increased slightly in the middle and late stage of fermentation,with an average relative abundance of 4%.According to the results of shotgun macrogene sequencing,the results of species annotation of macrogene sequencing were basically consistent with those of culturable method and 16 S r RNA sequencing.Bacteria occupied an absolute dominant position in the fermentation flora,fungi had a very low abundance in the whole fermentation process,and a small number of viruses were detected.The sequencing results of fermentation flora showed that amino acid metabolism and carbohydrate metabolism were the most active,and lactic acid bacteria(Staphylococcus,Pediococcus,Lactobacillus and weissella)were the main microorganisms involved in these two kinds of metabolism,which indicated that Aspergillus and other fungi were artificially inoculated in the starter making stage of Aspergillus Douchi,Bacteria are the key microbial community of Aspergillus Douchi flavor formation.The average temperature of traditional Aspergillus Douchi during koji making and post fermentation is about 30 ? and 45 ?.The koji making stage is salt free fermentation,and the salt content of Douchi during post fermentation is about 6%.The results showed that 16 kinds of free amino acids were detected in Douchi,and the total content of free amino acids increased gradually with the fermentation process,reaching 4.87 g / 100 g on the 21 st day after fermentation,while the content of fresh sweet amino acids was much higher than that of bitter amino acids;In terms of volatile components,the main flavor compounds were hydrocarbons,esters accounted for a relatively high proportion in the early stage,and the contents of aldehydes,pyrazines and acids increased in the middle and late stage.The flavor compounds with higher content(relative content > 1%)included acetic acid,2-Methylbutyric acid,3-methylbutyric acid,2-methylbutyraldehyde,methyl 2-methylbutyrate,isoamyl acetate,phenylacetaldehyde,cocoa aldehyde,benzoic aldehyde,pyrazine,etc2-pentylfuran and guaiacol were characteristic flavor compounds of fermented soybean products.The results of O2 PLS model construction [VIP(PRED)> 1.0] showed that there were 14 bacteria genera as the key bacteria genera,and the importance of Staphylococcus,Pediococcus,Lactobacillus and weissella was particularly prominent,and these genera were strongly related to free amino acids,organic acids,alcohols,esters,aldehydes,ketones,pyrazines and ketones.The results showed that the main volatile flavor components of Staphylococcus were aldehydes,ketones and acids;Bacillus is ketone,pyrazine and amine;Weissella,Pediococcus and Lactobacillus are acids and aldehydes.In this paper,from the two aspects of flavor and microorganism in the fermentation stage of Douchi,combined with a variety of analysis methods to explore the internal relationship between flavor formation and microorganism,clarified the important source of the formation of Douchi flavor,that is,the change of flora composition,and combined with the flavor determination after fermentation and cultivation of Douchi dominant microorganism to complete the preliminary evaluation.This will provide a research idea for further exploring the flavor formation law of Aspergillus Douchi,and establish the experimental basis and strain resources for the next step of compound fermentation.