Characterization Of Microflora And Their Functions On Flavor Compounds In Shaoxing Rice Wine

Shaoxing rice wine is one of the most famous Chinese rice wines with its long histroy. It is fermented with glutinous rice and wheat Qu. Due to the special fermentation process, the microflora is complex leading to an unique flavor style. Therefore, it would be important to investigate the microflora systematically, which would help us understand the fermentative mechanism of Shaoxing rice wine and the formation of flavor compounds, eventually improving its quality.In this paper, the modern biological technique of next-generation sequencing was employed to analyze the microbial dynamics during Shaoxing rice wine fermentation. And volatile compounds and organic acids were detected by HS-SPME/GC-MS and HPLC, respectively. Finally correlations between microbial compositions and flavor compounds were built by partial least squares regression. The main results were as follows:1. The diversities of bacteria and fungi in Shaoxing rice wine were rich, changes of which varied considerably.2. Bacterial communities analysis showed that Bacillus could be the most dominant in Shaoxing wheat Qu. And all of the analyzed sequences were distributed among ten major genera including Saccharopolyspora, Bacillus, Staphylococcus, Thermoactinomyces, Lactobacillus, Leuconostoc, Lactococcus, Weissella, Pseudomonas and Enterobacter during Shaoxing rice wine fermentation. The abundance of Bacillus, Staphylococcus and Thermoactinomyces increased gradually from 0 d to 4 d, and then decreased from 4 d to 24 d. While bacteria belonged to Lactobacillus, Leuconostoc, Lactococcus and Weissella had the opposite tendency, and they became dominant from 4 d to 24 d.3. Results of fungal communities indicated that most fungi belonged to Thermomyces in Shaoxing wheat Qu. And there were eight different dominant genera during Shaoxing rice wine fermentation including Aspergillus, Thermomyces, Candida, Saccharomyces, Cryptococcu, Epicoccum, Fusarium and Rhizomucor. Fungi belonged to Aspergillus were predominant, and they increased from 0 d to 4 d and from 9 d to 18 d. The abundance of Cryptococcu increased rapidly from 0 d to 4 d, but decreased from 9 d to 24 d. Also interestingly, fungi belonged to Cryptococcu, Epicoccum, Fusarium, Thermomyces and Rhizomucor achieved peak on the 9th day of fermentation.4. The volatile compounds during Shaoxing rice wine fermentation were quantified by HS-SPME/GC-MS, and the optimum conditions were that the samples were extracted by 50/30 μm DVB/CAR/PDMS fiber at 50℃ for 40 min, and the sample ethanol concentration was diluted to 3 %vol. The results showed that a total of 64 volatile compounds were identified in Shaoxing rice wine. Among these, esters and alcohols were the main ones. Meanwhile organic acids were analysed by HPLC. Lactic acid, acetic acid, succinic acid and citric acid had a higher concentration, and they could constitute the main organic acids in Shaoxing rice wine.5. Correlations between flavor compounds and microbial compositions were studied by partial least squares regression approach. The results demonstrated Pseudomonas and Enterobacter could be the major contributors to the formation of volatile compounds. And Lactobacillus, Leuconostoc and Enterobacter were correlated to such main organic acids. In fungi, a considerate relationship between Thermomyces, Epicoccum and Fusarium with eight kinds of volatile compounds was found. Furthermore Candida and Cryptococcus had a significant effect on esters and alcohols. Correlations that explained the formation of organic acids were mainly derived from Candida.