| Zhejiang rosy vinegar is a product that retains the entire characteristics of traditional techniques among seasonings,with a history of more than 100 years.With glutinous rice fed in April or May as the raw material,the vinegar is made through a series of procedures,such as saccharification,adding water,stirring,and low-temperature aging.Vinegar fermentation relies solely on the natural multiply of various microorganisms in the air in steamed rice.The dynamic balance of microorganisms is achieved through survival of microorganisms and screening of the environment;in the mean time,starch is saccharified,liquefied and acetified,thus affording a unique local product.In this study,we designed a fermenter to replace the traditional technique for the modern production of rosy vinegar.We studied the microbial community structures and functions during fermentation of Zhejiang rosy vinegar from the perspective of molecular ecology,and performed an analysis of the correlation between microorganisms and flavors by Bidirectional Orthogonal Partial Least Squares(02PLS),with the main conclusions as below:(1)An exceedingly high stirring frequency can lead to an exceedingly fast increase in the alcohol level,which will inhibit the yeast,produce a large quantity of residual reducing sugar,and reduce the final yield of rosy vinegar.An exceedingly slow stirring frequency results in the slow growth of yeast.The increased acidity of the rosy vinegar inhibits the yeast and reduces the final yield of the rosy vinegar.Employment of a pneumatic stirring fermenter and a mechanically stirred fermenter at a stirring frequency of 5 days per time for the production of Zhejiang rosy vinegar can increase the yield.Only the rosy vinegar in group 2-2 had a higher senscory score than the traditional rosy vinegar,and the sensory scores in the other rosy vinegar groups were significantly lower than in the traditional rosy vinegar,indicating that the Zhejiang rosy vinegar produced using a pneumatic stirring fermenter at a stirring frequency of 5 days per time was of the best quality.Therefore,this means can be used for the modern production of the Zhejiang rosy vinegar.(2)Determination of the 9 organic acids in the Zhejiang rosy vinegar samples by HPLC showed that the contents of organic acids in all the rosy vinegar samples were significantly higher than in the deep-fermented vinegar produced by means of self-priming fermentation.PCA and HCA analyses of the contents of organic acids revealed that the different stirring methods had significant effects on the production of organic acids in rosy vinegar,while the stirring frequency had fewer effects on the formation of organic acids in the rosy vinegar.The composition of organic acids in rosy vinegar produced via pneumatic stirring fermenter was similar to that in the traditional rosy vinegar.Determination of amino acids in the fermented rosy vinegar samples using a fully automatic amino acid analyzer indicated that amino acids showed an upward trend with the increase in the stirring frequency,indicating that the increase in the stirring frequency can increase the content of amino acids in the rosy vinegar.Determination of the volatile components in the fermented rosy vinegar by SPME-GC-MS showed that the content and the total amount of volatile components in all the rosy vinegar samples were significantly higher than in the self-priming fermented rice vinegar.The content and the total amount of volatile components in the rosy vinegar samples produced by the reflux stirring fermenter were significantly lower than in other rosy vinegar samples.PCA and HCA analyses of the content of volatile components showed that the different stirring methods had significant effects on the production of organic acids in the rosy vinegar,while that the stirring frequency had fewer effects on the formation of volatile components in rosy vinegar.The composition of volatile constituents of rosy vinegar produced using a pneumatic agitating fermenter was similar to the traditional rosy vinegar.The production method using the pneumatic stirring fermenter at 5 days per time produced good flavor,which could replace the traditional technique for the production of Zhejiang rosy vinegar and thus achieving its modern production.(3)Determination of the contents of organic acids during fermentation of Zhejiang rosy vinegar by HPLC showed that the content of lactic acid during fermentation of Zhejiang rosy vinegar primarily accumulated during flowering,which was slightly increased in the initial stage of fermentation while continuously decreased in the subsequent fermentation process.The contents of a-ketoglutaric acid and malic acid were not changed significantly with the fermentation,mainly accumulating during the flowering process.Succinic acid,acetic acid,oxalic acid,pyruvic acid,pyroglutamic acid and tartaric acid showed a trend of continued increase as the fermentation went on.The content of volatile components during fermentation of Zhejiang rosy vinegar was determined by SPME-GC-MS,and analyzed by PCA and HCA.During the first section of the fermentation process(Od?40d),the change in the volatile components in Zhejiang rosy vinegar was mainly concentrated on the first principal component axis,and mainly on the second principal component axis during the second section of the fermentation process,indicating that the types of aroma produced in the two fermentation stages were different.(4)Analysis of the bacterial phylum level during fermentation of Zhejiang rosy vinegar showed that a total of 5 phyla were found at Od,namely Proteobacteria(40.65%),Firmicutes(55.09%),Actinobacteria(4.04%),Bacteroidetes(0.21%),and Fusobacteria(0.011%).A total of 25 doors were found during fermentation of rosy vinegar,in which Proteobacteria and Firmicutes were the dominant phyla in the entire rosy vinegar fermentation process,with a relative abundance greater than 95%.With the progression of fermentation,the relative abundance of Proteobacteria continued to increase while that of Firmicutes continued to decrease.Analysis of the genera of bacteria during fermentation of Zhejiang rosy vinegar showed that the abundance of Acetobacter and Lactobacillus during fermentation reached more than 80%(a leading role).With the progression of fermentation,the Acetobacter genus continued to increase and eventually stabilized,and Lactobacillus continued to decline.Analysis of the fungal phylum level during fermentation of Zhejiang rosy vinegar showed that a total of 5 fungal phyla were found in the vinegar samples at Od,namely Ascomycota,Fungi unclassified,Basidiomycota,zygomycetes(Zygomycota)and Glomeromycota,where the relative abundance of Ascomycota was the highest,reaching 98.83%.The relative abundance of Ascomycetes showed a downward trend.The relative abundance of Basidiomycota was low in the early stage of fermentation,while increased with the progression of the final fermentation.Fungi_unclassified was also increased with the progress of fermentation,during which the main fungi included Ascomycota,Fungi unclassified,Basidiomycetes,Zygomycetes and Glomeromycota.The relative abundance of Ascomycota ranked the highest throughout fermentation,followed by Fungi unclassified and Basidiomycetes.Analysis of the fungal genera during fermentation of Zhejiang rosy vinegar showed that over 200 genera were found throughout fermentation of rosy vinegar.The relative abundance of Aspergillus,Candida,and Thermoascus were large in the early stage of fermentation.Although the relative abundance of Aspergillus was unstable during fermentation,it generally showed a downward trend.Candida persisted throughout fermentation.Its relative abundance at Od was very low(0.074%),while reached 26.7%at 10d.Its relative abundance showed a downward trend throughout fermentation(5)Analysis of the correlation between microorganisms and organic acids during fermentation of Zhejiang rosy vinegar using 02PLS yielded 22 bacterial genera with the importance index of bacterial independent variable greater than 1 and 38 fungal genera.Microbial genera and the organic acids during fermentation of rosy vinegar were subjected to correlation analysis,whereby microorganisms with good correlation with formation of organic acids were obtained.Analysis of the correlation between microorganisms and volatile components during fermentation of Zhejiang rosy vinegar using 02PLS yielded 28 bacterial genera with the importance index of bacterial independent variable greater than 1 and 46 fungal genera.These microorganisms and volatile components during fermentation of rosy vinegar were subjected to correlation analysis,whereby microorganisms with good correlation with formation of volatile components were obtained. |
PDF Full Text Request