Dynamic Analysis Of Microbiata And Physicochemical Properties During The Fermentation Process Of Baoning Vinegar "Herb Daqu"

Baoning vinegar is one of the most four famous vinegars in China.During its fermentation process,the starter“herb Daqu" is fermented with raw materials and produced in an open environment with natural ventilation.The entire fermentation process is easily affected by fluctuations of the external environment.It contains highly complex microbial communities,substances and enzymes.They are changeable in the whole fermentation time.In this study,the samples of the herd Daqu in whole fermentation process from different layers was colleceted in winter and summer,and we also sampled the matured herb Daqu in different seasons.The microbiota was analyzed by high-throughput sequencing technology and traditional culture method.Combined with the monitoring of the physicochemical proporties,we wanted to illustrate their dynamic changes during fermentation and the differences betwwen different seasons and layers.The RDA(CCA)and Spearman correlation analysis methods was used to analyse the correlation between microbiata and physical and chemical properties,and according to these,we explored the reason of dynamic changes of the microbiota and its differences betwwen different seasons and layers.The main results are as follows:1.The results of the microbial plate counts showed that the dynamic of the Aerobic plate count and Bacillus count in the samples of different layers in winter and summer seasons were roughly in the trend of first rising,then falling,and then rising again,while the dynamic changes of moulds and yeasts count were in the trend of first rising,then falling.The peak count results of the outer layer were higher than that in the inner one,and the plate count results were different betwwen the samples of different seasons and layers.Traditional culture method research on the bacterial flora showed that the culturable bacteria during the entire fermentation process of the herb Daqu fermented in winter mainly include Staphylococcus,Bacillus and Serratia.High-throughput sequencing results showed that,the dominant bacteria in the entire fermentation process of the samples in winter and summer inclued:Staphylococcus,Pantoea,Streptomyces,Saccharopolyspora,Kroppenstedtia and Bacillus.The dominant fungus were Rhizomucor,Aspergillus,Hyphopichia,Fusarium,Thermoascus and Thermomyces.The microbiota changed dynamically during the fermentation process,and the dominant microorganisms bettwen different seasons and layers were mainly different in relative abundance.2.The monitoring of physicochemical proporties indicated that the Baoning vinegar herb Daqu was a medium-temperature Daqu.The moisture content gradually decreased during the entire fermentation process.the pH value fluctuated around pH 7 in the middle and later stages.The starch content was remaining 70 g/l00g throughout the fermentation process.The reducing sugar content of the two seasons showed a general downward trend.For the saccharification power,its value in the outer layer samples of two seasons showed a trend of rising first and then decreasing.The peaks were both reaching on the 7th day,which were 1245 mg/g.h and 1161 mg/g.h,respectively.While in the inner layer,it showed a gradual decrease trend,and it decreased to 107.11 mg/g.h and 48.57 mg/g.h respectively at the end of the fermentation stage.During the whole fermentation process,the liquefaction power showed an overall upward trend.The esterification power was at a very low level at the beginning,and fluctuated after a sharp rise.The physicochemical properties of samples in different seasons and different layers were difference to some extent.3.From the perspective of genus level,the dominant bacteria of all matured herb Daqu were:Streptomyces,Pantoea,Staphylococcus,Scopulibacillus,Saccharopolyspora and Kroppenstedtia.The dominant fungus were Aspergillus,Thermomyces,Rhizomucor and Hyphopichia.They were basically consistent with the microbiota which in the fermentation process.Compared with other vinegar Daqu,Scoplibacillus,Kroppenstedtia,Kosakonia,Thermomyces and Hypopichia can be treated as the unique biomarkers of Baoning vinegar herb Daqu to distinguish it from other vinegar Daqu.There were significant differences in the physicochemical indexes of the matured Daqu in different seasons.The pH values were all around 7.The moisture content of the samples in summer was the lowest,but they were all slightly higher than the industry standard.The sample in summer had the highest starch content.the reducing sugar content was the highest in spring one;the saccharification and liquefaction power of the sample in spring were the highest,while the highest esterification power one was in winter.4.Correlation analysis showed that pH value,moisture content and temperature were the reasons caused the dynamic changes of the microbiota during the fermentation process and the differences between different seasons and layers of Baoning vinegar herb Daqu,which is consistent with the Daqu solid fermentation(SSF)process is actually thermotolerant and drought-resistant community,and the mocrobiota can adapt to the enviromental stress during SSF process.The microbiota changed with the variations of the environmental conditions,and in thus caused the changed of other physicochemical proporties and enzyme activities.5.The comparison of using traditional culture method and high-throughput sequencing technology to explore the bacterial flora of samples in winter showed that the bacteria including Staphylococcus,Bacillus and Serratia were both detected by the two methods,but some predominant bacteria present in the samples were only monitored by high-throughput sequencing technology,and the predominant bacteria detected at each fermentation stage were different.The combination of the two methods can more fully reflect the true information of the microbiota in same samples,and was conducive to the establishment of herb Daqu species library.