A Study On Flavor Compounds Of Raw Material And Fermentation Process For Apple Cider Vinegar

Apple cider vinegar is a healthy drink which obtained by two-step fermentation from apple(juice).It has a mixed flavor of apple and vinegar.It contains not only good flavor,but also many health functions.In recent years,the sales of apple cider vinegar drinks which made by concentrated apple juice increased rapidly.The concentrated apple juice was always used as raw material to produce apple cider vinegar in the large-scale industrial production.The quality of apple juice has an important influence on the quality of the products,especially the flavor of the products.At present,it is lack of a unified,objective evaluation standard.hat easily leads to the fluctuation of product quality.Meanwhile,it is not clear that the change rules of the main flavor compounds in the fermentation of apple cider vinegar because the domestic fruit vinegar industry started relatively late.In this paper,GC-MS and HPLC were used to analyze the different flavor compounds of concentrated apple juice,and the principal component analysis(PCA)method was used to select the main flavor compounds,and established an objective and effective method of distinguishing the flavor quality of apple cider juice.This can provide the basis for purchasing the raw materials.In the same time,the composition and changing rules of the main flavor compounds during the fermentation process of apple cider vinegar were analyzed.This can provide reference for clarifying the evolution laws and characteristics of flavor compounds of apple cider vinegar.In this study,the subject investigated contained two groups of concentrated apple juice,the samples of the first group have good flavor and another group has relatively poor falvor.The contents of soluble solids,total acidity,pH and reducing sugar were analyzed and compared.The result showed that the samples of two groups had no significant difference.Then,HSPME-GC-MS and HPLC were used to analyze the volatile flavor compounds,organic acids,amino acids and carbohydrates of the samples.The PCA was used to select 13 kinds of main flavor compounds from 63 kinds of flavor compounds which detected by the instruments above,including 6 kinds of volatile substances,2 kinds of organic acids,3 kinds of amino acids and 2 kinds of carbohydrates.The cluster analysis was used to analysis the relationship of the samples which based on 13 kinds of main flavor compounds.Then the similarity values were compared.Finally,the method was established to distinguish the flavor quality of the concentrated apple juice basing on the 5 kinds of compounds,including aspartic acid,serine,methionine,fructose and glucose.8 kinds of concentrated apple juice were selected randomly to verify the method.The results showed that the method could be used to classify the concentrated apple juice into good and poor flavor quality.The composition and changing rules of flavor compounds in the whole fermentation process of apple cider vinegar were analyzed.105 kinds of flavor substances in the alcoholic fermentation and 38 kinds of flavor substances in the acetic fermentation were detected respectively.The PCA was used to select 9 kinds of main flavor compounds and 4 kinds of characteristic flavor compounds from flavor compounds of fermentation.The changes of flavor compounds in the fermentation process showed that the volatile flavor compounds can be divided into 5 categories by the change regulaion and formation of the most compounds happened in the stage of alcoholic fermentation;the formation of the main organic acids happened in the medium and late stage of alcoholic fermentation and the late stage of acetic fermentation,and tartaric acid and acetic acid can be considered as characteristic organic acid respectively in the two stages fermentation;the amino acids can be divided into 4 categories by the change regulation and formation of the most compounds happened in the early stage of alcoholic and acetic fermentation,then the contents decreased;the contents of main carbohydrates decreased during the fermentation.The malic acid,lactic acid and methionine are the main flavor compounds which not only have important influence on the quality of the concentrated apple juice,but also considered as the main flavor compounds in the fermentation process.Then the evolvement laws and mechanism of the three compounds were preliminary explored.