| The production of Zhejiang Rosy Vinegar has a history of more than one hundred years.It is named "Rosy Vinegar" because of its bright color and bright rose-red which popular in hangjiahu area of Zhejiang province.The acetic acid fermentation of Rosy Vinegar was carried out for more than three months by Liquid Surface Static Fermentation.However,this fermentation process was restricted by many factors,which made it difficult to realize the mechanization and large-scale production of Rosy Vinegar.In this study,the influence of different specific reaction area Q(The ratio of the area of contact between fermentation liquid and air to the total mass of fermentation liquid)of the Rosy Vinegar fermentation process was explored based on stirring fermentation tank instead of the traditional ceramic tank.Kinetics of the fermentation process,the formation of flavor substances in the fermentation process and the flavor difference under different aging conditions were studied after selecting the ideal Q value.The main conclusions are given below:(1)Q value of 1.5 is the optimal Q value for the fermentation of Rose Vinegar in this experiment and too large or small Q value is not conducive to acetic acid fermentation.When the Q value is too large,the acetic acid generation rate is faster;the peroxidation phenomenon is more serious in the later stage of fermentation.Further,the loss of volatile acids occurs and higher in acetic acid was observed,so that the final yield of Rose Vinegar has dropped.While the Q value is too small,the oxygen supply of fermentation liquid per unit volume is insufficient,the activity of acetic acid bacteria will be reduced,the acetic acid content will rise slowly,and the final yield will be low.(2)The kinetic models were fitted in the process of fermentation.The results showed that the optimal growth kinetic model of yeast in the alcohol fermentation stage wasSGompert model with the determination coefficients of 0.986.The best model for reducing sugar consumption and alcohol production during alcohol fermentation is a Logistic model with the determination coefficients(i.e.0.999)and the model is fitted very well.The best kinetic model of acetic acid bacteria growth in the acetic acid fermentation stage is SGompert modele with the determination coefficient of 0.914,and the best model of alcohol consumption is DoseResp model,the coefficient of determination is 0.976.The formation of acetic acid is more suitable by linear fitting.The fitting equation is y=0.048x+0.754 with the determination coefficients of 0.992.(3)Determination of organic acids and volatile components by HPLC and SPME-GC-MS showed that the content of acetic acid and lactic acid are important organic acid in Rose Vinegar.In addition,the content of lactic acids is close to 3 times of acetic acid at the beginning of the fermentation.However,the lactic acid content decreased continuously while acetic acid content is increasing as the process of fermentation.On the other hand,less abundant organic acids like L-Maleic acid,Succinic acid,L-Pyroglutamic acid,Tartaric acid,Pyruvate,Oxalic acid were showed minor fluctuation in the fermentation process;which is also played an important role in the flavor of Rose Vinegar.PCA analyses of the volatile components were clearly showed that the Rose Vinegar fermentation process was divided into three stages.The characteristic volatile components in different fermentation stages are obtained from the VIP score and factor loading diagram.The results exhibited that Propanoic acid 2-hydroxy-ethyl ester,Decanoic acid ethyl ester,Hexanoic acid ethyl ester,and ethanol are the characteristic volatile components in the early fermentation stage.However,the important flavor substances were detected in the middle fermentation stage such as ethyl propionate,ethyl hexadecanoate and phenyl ethyl propionate.Furthermore,during late fermentation,other essential volatile components like Phenylethanol,ethyl phenylacetate,ethyl 2-methyl propionate,isovaleric acid,acetic acid,2,3-butanedione were observed.(4)Determination of organic acids and volatile components in Rosy Vinegar under different aging conditions by HPLC and SPME-GC-MS showed that the total content of organic acid was higher in aged vinegar under the storage of long-time room temperature and high temperature compared with short-term low temperature.The total content of alcohols,acids,and esters are less in vinegar under long-time room temperature and short-term hightemperature compared with short-term low temperature,while the total content of ketones and aldehydes are much higher.PCA and OPLS-DA analysis of the volatile components showed that vinegar can be distinguished obviously according to the aging conditions,and the vinegars of short-term high temperature are more close to the vinegars of long-time room temperature,which imply that high temperature may be shorten aging period.Then according the OPLS-DA S-plot and OPLS-DA loading factors diagram results,the important aroma components that separates different vinegars from different ageing condition and characteristic aroma components in Zhejiang rosy vinegar under each ageing condition are obtained. |
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