Effects Of Dynamic Changes Of Microbial Community Structure In Mixed-Bacteria Fermented Cheese On Fatty Acid Synthesis And Metabolism

Mold-ripened cheese is a cheese based on the fermentation of lactic acid bacteria and the secondary fermentation of mold to promote its ripening.Its saturated fatty acid content is high,the proportion of unsaturated fatty acid content is low,and only a small amount of fatty acid is converted into flavor substances.The microbial community structure of mold-ripened cheese is in a state of dynamic changes during the ripening process,and the interaction between them affects the unsaturated fatty acid content of mold-ripened cheese and the content of flavor substances converted from fatty acids.In order to explore the relationship between the microbial community structure and fatty acid synthesis and metabolism in the process of mold-ripened cheese maturation,this paper firstly prepared a mold-ripened cheese with secondary fermentation of Geotrichum candidum and Actinomucor elegans,and measured some basic indicators;then,using metagenomics and lipidomics technology combined with bioinformatics analysis methods,the relative changes of microorganisms and lipid metabolites in the mold cheese were identified,and differential metabolites and differential metabolic pathways were identified,and combined with differential microorganisms to analyze,revealing the microbial effects of this mold cheese on fatty acid synthesis and metabolism at different ripening stages.The main research results are as follows:1.A mold-ripened cheese was prepared by the mixed fermentation of Lactobacillus sp.,Geotrichum candidum and Actinomucor elegans.The measurement results of basic indicators found that from 0 to 8 days in the cheese ripening process,the p H value and Na Cl content showed an overall upward trend,and the moisture content,fat content and protein content showed a downward trend on the whole;it was found that there are 8 kinds of saturated fatty acids and 6 kinds of unsaturated fatty acids in cheese free fatty acids;29 kinds of esters,17 kinds of alcohols,14 kinds of acids and 5 kinds of ketones were found in the volatile flavor substances of cheese.2.The results of metagenomic functional annotation showed that most of the microbial activities during cheese ripening were related to carbohydrate metabolism,amino acid metabolism,etc.,and a small amount was related to energy metabolism and lipid metabolism.3.The results of metagenomic species annotation showed that 73 genus and 104 species of microorganisms were identified at the genus level and species level,respectively,during the cheese ripening process.Among them,Lactobacillus delbrueckii was negatively correlated with Bacteroides uniformis;Candida tropicalis was negatively correlated with Lactobacillus acidophilus;Bifidobacterium animalis,Streptococcus thermophilus,Streptococcus infantarius and Streptococcus pyogenes were negatively correlated is a positive correlation.4.Differentially expressed genes in different ripening stages of cheese showed that the activities of carbohydrate metabolism,amino acid metabolism,energy metabolism and lipid metabolism occurred in cheese were most active at 2 days of fermentation;lipid transport and metabolism and secondary metabolite biosynthesis,transport and fermentation such as catabolism is most active at 4 to 8 days.5.The fatty acid synthesis pathway was analyzed,and it was found that Fab B(β-ketoacyl-ACP synthase),Fab A and Fab Z(β-hydroxyacyl-ACP dehydratase)and FAS1/2(fatty acyl-Co A)appeared in cheese after 0 days of ripening.The correlation analysis between metagenes and free fatty acids shows that Streptococcus sp.,Bifidobacterium sp.,Lactobacillus sp.,etc.are positively correlated with oleic acid,Candida sp.,Aspergillus sp.,etc.are positively correlated with linoleic acid,linolenic acid,trans-oleic acid,etc.correlation,and negative correlation with oleic acid.6.The combination of differential metabolic pathways found by lipidomics and metagenomic analysis found that Candida sp.,Streptococcus sp.and Bifidobacterium sp.may be directly or indirectly involved in glycerophospholipid metabolism,fat digestion and absorption,and linoleic acid metabolism.Alpha-linolenic acid metabolism and arachidonic acid metabolism;Lactobacillus sp.may be directly or indirectly involved in linoleic acid metabolism,alpha-linolenic acid metabolism,arachidonic acid metabolism,glycosylphosphatidylinositol(GPI)-anchored biosynthesis and glycerolipid metabolism.This study clarified the relationship between the dynamic changes of microbial community structure in cheese and the synthesis and metabolism of fatty acids,especially the effect on unsaturated fatty acids,so as to improve the content of unsaturated fatty acids,improve the flavor and enhance the nutritional value of cheese.