| Shanxi aged vinegar,one of famous vinegar in China,is brewed using traditional solid-state fermentation technology.During the fermentation process,various microorganisms grow and produce many metabolites,which give the vinegar unique taste and flavor.Among them,organic acids,the main source of acidity,make up the body of the vinegar flavou.However,the knowledge of the the regular pattern of organic acids during fermentation is also not very clear,which hindered the development of vinegar industry greatly.In this paper,the changes of organic acids and microbial communities were analyzed to reveal the regular pattern of organic acids during fermentation process and increase the knowledge of fermentation theory.Firstly,The changes of physical and chemical properties and kinds of organic acids were analyzed during the alcohol fermentation and acetic fermentation of two workshops.The result showed that acetic acid and lactic acid were main organic acids.The acetic acid content of two workshops finally increased to 3916.3 mg/100g and 3255.9 mg/100g,respectively.Lactic acid were mainly produced in alcohol fermentation and lactic acid content increased to 2648 mg/100mL at the late of alcohol fermentation.Then the lactic acid content of two workshops both decreased during acetic acid fermentation integrally and the lactic content were 1324.2 mg/100g and 2002.6 mg/100g,respectively.Also,low content of oxalic acid,citric acid,malic acid,tartaric acid,pyruvic acid and succinic acid were detected and they changed unregularly.Smart tongues were used to detect samples from different periods of acetic fermentation.Results showed that the samples could be distinguished with the data acquired from the electronic tongues.Furthermore,back propagation neural network(BP NN)was used to construct a model for quantitative prediction of acetic acid and lactic acid.For the testing samples,the correlation coefficients of acetic acid and lactic acid between observed and predicted values were 0.9615 and 0.9942 and the root mean standard errors of prediction were 54.4 mg/100g for acetic acid and 59.0 mg/100g for lactic acid,respectively.Thus,this research suggested a spot rapid method to analyze key organic acids.PCR-DGGE method was used to analyze the bacterial community during fermentation process.Results showed that most of bacteria during alcohol fermentation were lactic acid bacteria and the bacterial diversity increased gradually.At the stage of the acetic acid fermentation the species and quantity of lactic acid bacteria were both decreased and acetic acid bacteria appeared and increased gradually.The bacteria diversity increased first and then decreased during the whole acetic acid fermentation.Canonical correspondence analysis(CCA)was used to analyze the relationship between bacterial community and organic acids.Results showed that bacteria which contribute to acetic acid formation were Acetobacter pasteurianus>Gluconacetobacter liquefaciens>Lactobacillus panis>Lactobacillus helveticus,and bacteria which contribute to lactic acid formation were Lactobacillus reuteri>Lactobacillus malefermentans>Lactobacillus fermentum,respectively.Changes of microorganisms and bacteria diversity were probably the main reason for the difference of organic acids in two batches of samples.Some lactic acid bacteria and acetic acid bacteria screening from cupei were cultivated at 40? for 96 h and the organic acids in fermentation broth were analyzed by HPLC method.It turned out that lactic acid and acetic acid were main organic acids produced by lactic acid bacteria and acetic acid bacteria respectively.Meanwhile they also produced many other kinds of organic acids including citric acid,malic acid,pyruvic acid,succinic acid and so on.The tested lactic acid bacteria(Lactobacillus casei CP-L5?Lactobacillus sp.CP-L9)and acetic acid bacteria(Acetobacter pasteurianus CP-A11?CP-A12?CP-A13)behaved the obvious characteristic of producing acidity and they could be used for further research. |
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