Screening Of Excellent Acetic Bacteria Strain For Greengage Vinegar Fermentation And Optimization Of Brewing Process

Greengage vinegar are characterised by a high acid content and the lack of specialised acetic acid bacteria for greengage vinegar making has led to problems such as long fermentation cycles,low ethanol conversion and lack of typical flavor in the production of greengage vinegar.Therefore,the selection and breeding of special acetic acid bacteria with acid tolerance for greengage fruit vinegar brewing is the key to improve the quality of greengage fruit vinegar.In this study,the selection and breeding of acetic acid bacteria for the brewing of greengage fruit vinegar,the optimization of acetic acid fermentation process and the changes of flavour substances and antioxidant activity in fermented greengage fruit vinegar were studied in depth to provide theoretical basis for the production of fermented greengage fruit vinegar.The main research contents and conclusions are as follows.（1）A strain J-27 with a high capacity for acid generation was screened using plate separation,acid production,and greengage vinegar fermentation experiments.The strain was fermented in greengage wine that has an initial ethanol concentration of 6%(v·v^-1).The overall acid concentration of greengage vinegar after fermentation was 45.51 g·L^-1.Acetobacter tropicalis strain J-27 was discovered using the 16S r DNA sequencing.Further mutagenesis of the strain J-2736 was performed at ambient pressure using plasma mutagenesis.The fermentation broth had 62.43 g·L^-1of total acid,which was 37.3%more than the parent strain J-27.It rose by 241.9%and 182.1%,respectively,as compared to Acetobacter pasteurianus HN1.01 and AS1.41.Additionally,Strain J-2736 was able to resist a p H of 2.6,10%(v·v^-1)ethanol,and 40 g·L^-1acetic acid.The results indicated that the acetic acid strain J-2736 exhibited excellent acid and ethanol resistance and high ethanol conversion,making it suitable for application in greengage vinegar production.（2）By whole-genome resequencing of tropical Acetobacter J-27 and J-2736,the main pathway involved in acid resistance of J-2736 was identified,and the difference in fermentation performance of the two strains was investigated.A total of 217 SNPs and 54In Dels variation points were obtained.The key mutation gene related to acid tolerance of Tropical Acetobacter J-2736 was CIW82.（3）On the basis of a single factor experiment,the effect of three factors on the selection of greengage fruit vinegar acetic acid fermentation was investigated:the initial p H value,fermentation temperature,and initial ethanol content.The experiment resulted in a greengage fruit vinegar fermentation total acid content and sensory evaluation score for the response value.Through a response surface optimization experiment,the optimal process conditions for greengage fruit vinegar fermentation were determined,namely:The fermentation temperature was set to 30°C,the initial ethanol concentration was 6%(v·v^-1),the initial p H value was 3.1,the total acid concentration was 64.85 g·L^-1,and the sensory score was 93.1.（4）The main metabolites in the fermentation process of greengage vinegar were analyzed.Glucose and fructose were the primary sugars in greengage vinegar,accounting for99.7%of the total sugar content,which continued to decrease throughout the fermentation process.Citric acid and acetic acid were the primary organic acids,accounting for 97.4%of total organic acids and increasing consistently during fermentation.Glutamic acid,threonine,alanine,valine,leucine,arginine,and lysine were the major amino acids,accounting for63.8%of the total amino acid composition.The most abundant volatile flavor chemicals were ethyl acetate,iso-amyl acetate,iso-amyl alcohol,acetic acid,iso-amyl acid,benzaldehyde,isoamyl aldehyde,acetaldehyde,and 3-hydroxy-2-butanone,which accounted for 93.5%of the total volatile flavor compounds and continued to grow.Together,these metabolites form the sensory system of greengage vinegar,which imparts its distinct flavor.（5）Greengage vinegar had a scavenging rate of 79.7%for DPPH and 39.5%for ABTS free radicals,respectively,and a reducing power of 86.49 g·m L^-1（converted to Vc）.DPPH free radical scavenging rate,ABTS free radical scavenging rate,and reducing power of greengage vinegar were raised by 1.5%,10.8%,and 71.7%,respectively,as compared to greengage juice.Greengage vinegar increased the DPPH free radical scavenging rate,the ABTS free radical scavenging rate,and the reducing power of greengage juice and greengage wine by 13.1%,22.5%,and 128.3%,respectively,indicating that greengage vinegar has more antioxidant properties than greengage juice and greengage wine,implying that greengage vinegar is worth developing and applying.