Study On The Formation Pathways And Control Of Furfural In Zhenjiang Aromatic Vinegar

Chinese traditional brewed vinegar,also known as grain vinegar,has rich taste and unique flavor.As an indispensable acid condiment in our daily life,traditional Chinese vinegar is rich in amino acids and sugars,which was conducive to the formation of5-hydroxymethylfurfural(HMF)and furfural.Furfural,as a key flavor contributor to the unique sweet aroma of Chinese vinegar,is often used as a quality parameter for thermal processing.However,the presence of excessive furfural will have potential adverse effects.This paper aims to clarify the formation mechanism of furfural in the production process of Zhenjiang aromatic vinegar,including the main stages of furfural formation,precursors and formation pathways.At the same time,the influencing factors of furfural formation and the inhibitors that can be applied are studied.Fifty-eight commercial vinegars from five regions of Zhenjiang,Shanxi,Sichuan,Fujian,and Tianjin,which were relatively common on the Chinese market,were selected to quantify and discuss the furfural,sugars,free amino acids,and organic acids content in vinegar in these different regions.It was found that the content of furfural in all vinegar samples ranged from 4.35 mg/L to 313.95 mg/L,with an average value of 136.71 mg/L.The relationships among the levels of furfural,free amino acids,sugars,and organic acids was investigated and evaluated by partial least squares regression(PLSR).Furfural was significantly positively correlated with xylose,deoxyribose and sucrose.Acetic acid and lactic acid are the two main organic acids in all vinegars.Taking Zhenjiang aromatic vinegar as an example,the entire production process was tracked and sampled to monitor the changes in furfural and HMF content.It was found that furfural was mainly produced during the decocting process,and HMF was formed in the decocting and subsequent aging process.A model of grain vinegar simulation liquid rich in sugars,amino acids and organic acids was first constructed to explore the potential precursors and mechanisms of furfural formation.It was found that the formation of furfural coexisted in multiple ways:(i)Maillard reaction of sugars and nitrogen-containing compounds was the main way,(ii)the direct cleavage of pentoses was the secondary way,and(iii)a minous pathway of the indirect conversion of pentosans.The formation of furfural from HMF or L-ascorbic acid does not occur in vinegar.Ribose,xylose,arabinose,amino acids,galacturonic acid,glucuronic acid and pentosan are all precursors formed by furfural,mainly xylose,arabinose,ribose,and amino acids.The wheat bran and rice husk used in acetic acid fermentation contain a large amount of pentosan,which is the source of the precursor sugar of furfural in Zhenjiang vinegar.The pentose in the fermentation broth is mainly derived from wheat bran.The acid soaking experiment of wheat bran and rice husk was used to simulate the acetic acid fermentation process,and the influence of acidity and enzymes on the content of xylose,arabinose and pentosan in the system was explored.It was found that the higher the acidity,the free xylose and arabin in the system.The higher the sugar content,and the greater the impact of acidity on the release of arabinose.The addition of cellulase,hemicellulase,pectinase,and xylanase showed varying degrees of influence on the sugar content in the wheat bran and rice husk soaking liquid.When xylanase was added,pentose and xylose were more,there was more xylose dissolved in the system.The possible influencing factors of furfural formation in the process of vinegar decoction were studied,and it was found that the type and amount of added sugars had an effect on the formation of furfural and HMF.The content of furfural depends on the added amount of ribose,xylose and arabinose.Acidity was the key factor for the content of furfural and HMF in Zhenjiang vinegar after decocting.The content of furfural compounds in decocted vinegar was related to the initial acidity of raw vinegar before decoction.The higher the acidity,the higher the content.The addition of fried rice is an important reason for the increase of HMF,but the furfural content is slightly decreased after adding parched rice color.Phenolics have a greater impact on the formation of furfural compounds in the process of decocting vinegar.The content of furfural and HMF in vinegar with vanillic acid,protocatechuic acid and chlorogenic acid was significantly higher than that of other groups,while catechins and epir Teas have an inhibitory effect on the formation of furfural and HMF.The addition of Na Cl can promote the formation of furfural and HMF to a certain extent.Finally,the formation kinetics of furfural in Zhenjiang aromatic vinegar during vinegar decoction was studied.The kinetic equation was established with different vinegar decocting temperature,different vinegar decocting time and furfural content after decocting vinegar.It was found that the vinegar decocting temperature and time had a great influence on the formation of furfural.At 80℃ and 95℃.Different inhibitors inhibit furfural and HMF to different degrees.The content of furfural and HMF decreased with the increase of Cys and GSH.The inhibitor of appropriate concentration has little effect on the flavor and physical and chemical composition of Zhenjiang aromatic vinegar.Cys and GSH show strong inhibitory effects in a short time of heat treatment,which is caused by the sulfhydryl group on Cys.The above findings can provide theoretical guidance and technical support for regulating the formation of furfural in Zhenjiang aromatic vinegar,and are of great significance for improving the quality stability of vinegar products and the improvement of product flavor.