Study On Microbial Diversity And Its Effect On Quality During The Spontaneous Fermentation Of Flat Peach Wine

Flat Peach is a natural hybrid variant of Prunus ferganensis with a unique flavor and rich nutrition.It is a typical respiratory leap fruit and winemaking through complex biochemical reactions is an effective way to overcome its seasonal defects.Under natural conditions,a complex and dynamic microbial ecosystem exists on the surface of the flat peach,and they play an important role in ensuring the health of the fruit and facilitating its conversion into flat peach wine.In order to clarify the evolution of microbiota and quality changes during the spontaneous fermentation of flat peach wine,this study used ITS/16S r RNA amplicon sequencing technology combined with traditional culturable microbial isolation techniques to study the diversity and structural changes of the flat peach wine community during the epidermis and spontaneous fermentation of flat peach wine,and to explore the enzyme-producing and fermentation characteristics of the isolable strains.The composition of physicochemical indicators,functional components,antioxidant activity,color parameters,organic acids and soluble sugars during the fermentation of peach wine was also determined.We also monitored the dynamic changes of volatile flavor substances by headspace solid-phase microextraction combined with gas chromatography dual mass spectrometry（HS-SPME-GC-MS/MS）,constructed microbial and physical and chemical quality indicators and flavor correlations based on multivariate data analysis,and combined PICRUSt2 software and KEGG,Meta Cyc and COG databases to perform functional prediction analysis of microbial flora structure during the spontaneous fermentation of flat peach wine.The specific research results are as follows:（1）Study on the diversity of microbial communities and fermentation characteristics during the spontaneous fermentation of flat peach wine.A total of 92 strains were isolated from the epidermis of Ingel peach of Shihezi 143rd regiment by culturable isolation technique.After molecular identification,the isolated yeast strains were found to belong to 8 genera and 12 species,including Filobasidium,Rhodotorula,Hanseniaspora,Rhodosporidiobolus,Pichia,Naganishia,Kazachstania,and Wickerhamomyces.Twelve strains of bacteria were identified in 6 genera and 10 species,which were Bacillus,Tatumella,Pantoea,Phytobacter,Enterobacter,and Rosenbergiella.The strains Pichia fermentans P4,Wickerhamomyces anomalus P10 and Hanseniaspora uvarum P43 had high enzyme-producing activity and good tolerance to p H,ethanol,glucose and SO₂,all of which were suitable for the brewing of flat peach wine.The results of high-throughput sequencing showed significant differences in the structural composition of microbial communities at different stages of fermentation.Kazachstania,Pichia,Aspergillus,Fructobacillus,Leuconostoc and Lactobacillus were the dominant genera during the spontaneous fermentation of flat peach wine.（2）Study on the dynamic change pattern of quality during the spontaneous fermentation of flat peach wine.The physicochemical indicators,functional components,color parameters,antioxidant activity,organic acids,soluble sugars and volatile compounds of the samples were studied during the spontaneous fermentation of flat peach wine.The results showed that the p H and total sugar content gradually decreased during the fermentation process and remained constant at the later stage of fermentation,while the total acid content showed an increasing trend.After spontaneous fermentation,the alcoholic content of flat peach wine reached 9.4±0.2%（v/v）and did not change anymore.The content of total phenols and total flavonoids first increased and then slowly decreased and stabilized.Spontaneous fermentation promoted the scavenging ability of ABTS⁺free radicals,the enhancement of DPPH free radical scavenging rate and the color of the wine.At the beginning of fermentation,tartaric acid,malic acid and citric acid were the main organic acids,and citric acid showed an overall increasing trend during the fermentation process.The soluble sugars during the spontaneous fermentation of flat peach wine were mainly sucrose,glucose,sorbitol and fructose,while the total content of soluble sugars decreased with the increase of fermentation time.Based on the HS-SPME-GC-MS/MS method to analyze the volatile compounds during the spontaneous fermentation of flat peach wine,a total of 53 volatile compounds were detected.Esters,alcohols and acids are the main contributors to spontaneous fermented flat peach wine,and low levels of volatile substances such as aldehydes and ketones may also affect its taste.（3）Analysis of quality and microbial correlations during spontaneous fermentation of flat peach wine.Multivariate data analysis was used to investigate the relationships between microorganisms and microorganisms,and between microbial genera and physicochemical and flavor indicators during the fermentation of flat peach wine.The fermentation process exhibited symbiotic relationships between the core microbial genera.Prediction of microbial functions using PICRUSt2 software revealed that the fungal community had the majority of functional pathways related to biosynthesis and precursor metabolite and energy production throughout the fermentation process.Bacterial communities related to biosynthetic functions were in the majority and had the most active metabolic functions at the end of fermentation.RDA analysis showed that changes in physical and chemical indicators in the fermentation environment could drive microbial community succession,especially quality indicators such as p H,total sugar,total acid,alcohol,citric acid,and sucrose could significantly affect microbial survival.According to the correlation analysis between microflora and volatiles,14 fungal and 11 bacterial genera were the main contributors to the production of volatile compounds during the spontaneous fermentation of flat peach wine.Some alcohols（ethanol,3-methyl-1-butanol,and 1-hexanol,etc.）,and esters（ethyl lactate,octyl formate,and isoamyl lactate,etc.）were well associated with yeast genera such as Kazachstania and Pichia,which are common in fruit wines.Among lactic acid bacteria,Fructobacillus,Leuconostoc,Lactobacillus and Weissella showed positive correlations with ethanol,isoamyl alcohol,isoamyl lactate and ethyl lactate.Overall,the microbial communities varied during the spontaneous fermentation of flat peach wine,and the overall quality of flat peach wine was related to the metabolic activity and fermentation behavior of microorganisms.