Analysis Of Volatile Components And Study On Age Discrimination Of Zhenjiang Aromatic Vinegar

Zhenjiang aromatic vinegar is Chinese typical fermentative food. It is famous for its color, aroma, acid, mellowness and denseness. Aroma is one of the most important sensory qualities of Zhenjiang aromatic vinegar, which is the result of kinds of volatile components in vinegar. But the present research on the he volatile compents of Zhenjiang aroimatic vinegar remains to be further in-depth,such as how do they change in the production and aging process,which have the odour activity,and what they have relations to the quality of Zhenjiang aromatic vinegar and vinegar ages and so on.This study had an comprehensive analysis on the generation and evolution of aroma of Zhenjiang aromatic vinegar and the influence of vinegar ages to the aroma, using Solid phase micro extraction (SPME), Gas chromatography-mass spectrometry (GC-MS) and GC-Olfactometry(GC-O),from production process to aging process,from the overall volatile compounds to the odour active compounds which has direct effect on the aroma. In addition, the ages of vinegar were marked confusedly currently on the market, so, we urgently need scientific ways to correct and recognize the ages of vinegar. We used volatile components of different ages of vinegar, odour active compounds and their odour activity value (OAV) and electronic sensory technology(electronic nose,electronic tongue and the fusion of two techniques) to tell differences from different ages of vinegar and to build up some corresponding methods to identify vinegar age.So wo can discriminate the ages of Zhenjiang aromatic vinegar correctly and rapidly.The main contents of this paper were as follows:1. Study on the volatile components in Zhenjiang vinegar changes in the process of production. By using SPME-GC-MS, we analyzed volatile compositions of Zhenjiang aromatic vinegar during each production stage (including accessories). Totally108kinds of volatile components were detected, in which, esters were most, and followed by heterocyclic compounds. Because the environment of solid-state vinegar is very conducive to the proliferation and fermentation of yeasts, the number of esters reached the maximum in the fermentation medium term of the acetic acid fermentation; Besides furfural, the contents of most heterocyclic compounds were very low in production stage of Zhenjiang vinegar, mainly from the cooking of raw material,"Chaomi" color and the fried phase of vinegar. Acetic acid,3-methyl butanoic acid,2-methyl butanoic acid and hexanoic acid and ethanol, Phenylethanol,3-methyl-1-butanol and2-methyl-1-butanol were the main acid and alcohol compounds in the production of Zhenjiang aromatic vinegar, respectively mainly produced in the alcohol fermentation and the acetic acid fermentation stage. Short chain fatty aldehyde was mainly produced in the raw material of cooking (liquefaction and saccharification). Zhenjiang vinegar’s saccharification and "Chaomi" color and the fried phase of vinegar all requried the heat treatment, which is good for the generation of two kinds of aromatic aldehyde namely benzaldehyde and phenylacetaldehyde..2,3-butanedione and3-hydroxy-2-butanone were the main two kinds of material of ketones in the production process of Zhenjiang vinegar, and the precursor compounds from the synthesis of tetramethyl pyrazine. Acetic acid fermentation stage especially the late stage were the main stage of generation of3-hydroxy-2-butanone. The solid-state acetic acid fermentation avails the production of3-hydroxy-2-butanone.2. Study on the changes of volatile composition of different ages of Zhenjiang vinegar.By using SPME-GC-MS,we analyzed the changes of contents of volatile components of Zhenjiang aromatic vinegar in6kinds of different vinegar ages of the new vinegar and the age of6,12,18,48and78months.â‘ 88kinds of volatile components were identified and heterocyclic compounds and ester compounds were most which respectively reached27and18kinds.With the increase of ages of vinegar, the number of volatile component of Zhenjiang vinegar increased. Overall aging of Zhenjiang aromatic vinegar had less influences on the acid compounds of volatile components, most of the alcohol content were significantly higher in the new vinegar than in the aging of Zhenjiang aromatic vinegar, Aging is conducive to the increase of content of ethyl acetate and some other ester. Phenylethanol, benzaldehyde,3-hydroxy-2-butanone,2,3-butanedione, phenyl ethyl acetate and ethyl acetate were the highest content of alcohols,aldehydes,ketones and esters of Zhenjiang aromatic vinegar respectively.â‘¡2-methyl-l-butanol/3-methyl-1-butanol contents’ratio in Zhenjiang vinegar had good stability, which could as a reference to identify the authenticity of Zhenjiang vinegar’s.â‘¢The change of heterocyclic compounds was the most significant in the aging process of Zhenjiang aromatic vinegar. With the increase of age of Zhenjiang aromatic vinegar, the number of heterocyclic compounds increased significantly. The change was mainly caused by pyrazine and oxazole compounds. Pyrazines are the most substance in heterocyclic compounds, most of their contents increased obviously with the increase of age of vinegar.2-ethyl-4,5-dimethyl oxazole and other three kinds of oxazole compounds were firstly discovered in Zhenjiang vinegar in this work. The content of oxazole compounds increased significantly with age. The various varieties and high content of heterocyclic compounds were the important reasons for the characteristic flavor and odor of Zhenjiang vinegar especially the vinegar with larger age.â‘£Benzaldehyde, trimethyl pyrazine,,2,6-diethyl pyrazine, tetramethylpyrazine, trimethyl oxazole can better characterize the change of the age of Zhenjiang aromatic vinegar, which can serve as important marker of the changes of age of Zhenjiang vinegar.3. Study on the odour active compounds of Zhenjiang vinegar with different ages.â‘ The DB-WAX and DB-5MS as two different polarity columns, combined with AEDA, were simultaneously used for the analysis of odour active compounds in Zhenjiang vinegar with four different ages of the new vinegar and the age of12,48and78months.Two odour active compounds were firstly discovered in Zhenjiang vinegar,one was3-(methylthio)-propanal whose content was rare (less than GC-MS instrument detection limit) but extremely important to the unique aroma of Zhenjiang vinegar (aroma dilution factor (FD)>2048).Another was2-ethyl-4,5-dimethyl oxazole, whose FD factor was obviously increased with age of Zhenjiang aromatic vinegar.â‘¡AEDA and direct strength method, as two sniffing analysis methods, were used and combined to analyze the odour active compounds in Zhenjiang aromatic vinegar with four different ages. It was found that3-methyl-butanal,2,3-butanedione and3-methyl butanoic acid in the four different ages of vinegar, whose aroma intensity≥3and FD>256, were the basic components in Zhenjiang aromatic vinegar’s aroma.â‘¢The results of GC-O showed that differences of the flavor profile between the new vinegar and the aging vinegar were very apparent.The differences of heterocyclic compounds (mostly with almond flavor and taste, and strong smell) and esters with softer (mostly with fruity and sweet, and softer smell), especially the heterocyclic compounds, which were one of the main reasons for the characteristic differences of Zhenjiang aromatic vinegar’s flavors with different ages.4. Study on the recognition of different ages of Zhenjiang aromatic vinegar based on the volatile constituents and odour active compounds.â‘ The contents of volatile components and the OAV of the odour active compounds in Zhenjiang aromatic vinegars with different ages were analyzed by principal component analysis (PCA) and cluster analysis (CA),the results showed that the new vinegar and the long aged ones could be distinguished from other ages obviously, but the result was not very ideal for identifying the vinegars with short aging time and close ages.In addition, compared results of PC A and CA, it can be seen that the change of volatile components is mainly related with some components which make small contributions to the characteristic aroma in the short aging process of vinegar.â‘¡According to volatile components and the odour active compounds, LDA on can effectively separate the Zhenjiang aromatic vinegars with6different ages. The recognition rate in the training set and testing set reach was achieved with100%respectively. But the LDA result based on odour active compounds could more clearly reflect the different changes between Zhenjiang vinegar of different ages and show more accurate characterizations of the internal relations between them.5. Study on the recognition of Zhenjiang aromatic vinegar with different ages using the electronic sensory technology. Electronic nose and electronic tongue were combined to analyze the Zhenjiang aromatic vinegar with6different ages.â‘ In the recognition of different ages of Zhenjiang aromatic vinegar using electronic nose technique, LDA, support vector machine (SVM) and back-propagation neural network (BPNN) were used to build up models to recognize vinegar age.The result showed that the performance of BPNN was better than that of LDA and SVM,whose recognition accuracy rate in the training set and test set achieved98.75%å'Œ97.5%respectively.â‘¡Electronic tongue with LDA model and multi-sensor fusion (electronic nose and electronic tongue) with LDA model could distinguish the6different ages of Zhenjiang vinegar. The identification rate in the training set and testing set of these models all achieved100%; however, samples from the same age gathered closer in multi-sensor fusion (electronic nose and electronic tongue) with LDA model, and the boundaries between different groups were more obvious.