Research On High Quality Apple Cider Vinegar And Its Flavor

As a new type of fermented food,apple vinegar not only has a unique flavor,soft taste,but also has uniform texture,rich in nutrients and flavor substances.Using apple as raw material,apple vinegar is made by juicing,adjusting acid and sugar,alcohol fermentation,acetic acid fermentation and aging.The process of alcohol fermentation and acetic acid fermentation is especially important.Yeast and acetic acid bacteria are the most important strains in the fermentation process.In this study,firstly,the process of alcohol fermentation and acetic acid fermentation were optimizes,and the changes of main nutrients during fermentation were analyzes.In order to explore the effect of mixed fermentation using two bacteria,on the basis of single-fermentation fermentation,the process of mixed fermentation of tropical yeast and raw yeast was carried out,and the changes of organic acids,free amino acids and volatile flavor substances in the fermentation process were explored.The differences between the two fermentation methods were analyzed;the results can provide some reference for enriching the aroma substances of apple vinegar.The main findings are as follows:(1)Research on the fermentation process of apple vinegar.The single factor and response surface experimental design method were used to optimize the fermentation process of apple vinegar fermentation.The experimental results showed that the fermentation process was better at the fermentation temperature of 28°C,pH 4.5,fermentation time 72 h,and inoculum of 11 %.Using these conditions the alcohol content is 6.15 %.The preferred process for acetic acid fermentation: the rotation speed is 150 r/min,the fermentation temperature is 31°C,the inoculum is 10 %,and the initial alcohol content is 6.5 %.The total acid content under this condition was 51.35 g/L.(2)Nutritional analysis of apple cider vinegar during fermentation.The main physical and chemical indicators of the products in different stages of apple vinegar fermentation were tested,including total acid,protein,polysaccharide,polyphenol and flavonoids.Antioxidant properties mainly including DPPH free radicals,hydroxyl radicals,ABTS radicals and superoxide anion radical scavenging rates were analyzed.The results indicated the content of polysaccharides and protein decreased gradually with the increase of fermentation time.The changes of polyphenols and flavonoids were the same.The content of polyphenols and flavonoids increased during the stage of apple wine,but they decreased during the stage of apple vinegar,and the changes of antioxidants were the same as the changes of polyphenols and flavonoids flavonoids contents.(3)Effect of mixed fermentation on the flavor of apple vinegar.The inoculation ratio of aromatizing yeast and Candida tropicalis was determined by single factor experiment.The optimal inoculation ratio of aromatizing yeast and Candida tropicalis was 1:2 based on alcohol content and cell concentration.Mixed fermentation can increase the content of organic acids(9.03 g/L),can increase the content of umami(1236.71 mg/L)and sweetness(858.25 mg/L)in amino acids,and can improve the type and content of aroma substances(34 species,8.62 mg/L),the key flavor compounds of apple vinegar were identified by odor activity value and principal component analysis,they were ethyl benzoate,ethyl acetate,isoamyl acetate,acetic acid,phenylethyl alcohol,phenylacetaldehyde,furfural.Compared with acetoin,the mixed fermentation apple vinegar has the highest comprehensive score(1.06).The sensory score of the mixed fermentation apple vinegar was higher than that of the single-fermented apple vinegar,and the quality of apple vinegar was better.The results indicated that,in the process of apple vinegar fermentation,mixed fermentation using fragrant yeast and Candida tropicalis is an effective way to improve the aroma quality of apple vinegar.By adjusting the inoculation ratios of the two strains,the aroma quality can be obtained.The results can provide refers to the production of high qulity apple vinegar in the large scale liquid fermentation.