Analysis of Saccharification Products of High-Concentration Glutinous Rice Fermentation by Rhizopus nigricans Q3 and Alcoholic Fermentation of Saccharomyces cerevisiae GY-1

Unraveling the microbial community and succession during the maturation of Chinese cereal vinegar Daqu and their relationships with flavor formation

Daqu, the fermentation starter of Shanxi aged vinegar (a traditional Chinese cereal vinegar), is produced by natural fermentation of barley and/or peas under conditions of open environment. However, the succession of microbial communities and its effects on volatile compounds during Daqu maturation were still unclear, which are closely related to the flavor and quality of Shanxi aged vinegar. In this study, the dynamics of physicochemical properties, microbial communities, and volatile compounds and their inter-relationships during the production of Shanxi aged vinegar Daqu were investigated. High-throughput sequencing analysis showed that Lactobacillus and Rhizopus were the most abundant bacteria and fungi during Daqu maturation, respectively. Co-occurrence network analysis showed that Lactobacillus, Saccharopolyspora, Leuconostoc, and Weissella were the important taxa affecting the diversity of Daqu microbial community. Spearman correlation analysis showed that Leuconostoc, Aspergillus, Rhizopus, and Wickerhamomyces were positively correlated with starch and reducing sugars; Wickerhamomyces, Aspergillus, and Bacillus were positively correlated with esterification; Lactobacillus, Enterobacter, Bacillus, Aspergillus, and Rhizopus were positively correlated with lactic acid and acetic acid. Based on the Mean Decrease Accuracy index analysis showed that, ethyl acetate, 1-nonanal, 1-octen-3-ol, ethylbenzene, 3-furanmethanol, and methyl isovalerate were the volatile characteristic compounds during Daqu maturation, respectively. Aspergillus, Byssochlamys, Lichtheimia, Rasamsonia, Rhizopus, Syncephalastrum, Enterobacter, Lactobacillus, Leuconostoc, and Staphylococcus were strongly correlated with volatile compounds; among them, fungi had a greater impact on volatile compounds than bacteria. This study may further improve our understanding concerning the microbial system and microbial roles of Chinese cereal vinegar Daqu and may contribute to optimize the production process of Daqu.

Isolation and Evaluation of Rhizopus arrhizus Strains from Traditional Rice Wine Starters (Jiuqu): Enzyme Activities, Antioxidant Capacity, and Flavour Compounds

Seventy-eight autochthonous strains of Rhizopus arrhizus were isolated from rice wine starter samples across twenty-nine regions in China to evaluate their potential in traditional rice wine fermentation. Strains were assessed for enzyme activity, antioxidant properties, amino acid production, and volatile flavour compounds. Significant variation in enzyme activities was observed, with acidic protease activity ranging from 280 to 1023 U/g, amylase from 557 to 1681 U/g, and esterase from 370 to 2949 U/g. Strains W17 and W42 exhibited the highest enzyme activities and antioxidant capacities, with a total phenolic content of 828 mg/L, total flavonoids of 215 μg/L, and an ABTS scavenging rate of 96.3%. They also produced high levels of glutamic acid (up to 3083 mg/L), enhancing the flavour profile. Histamine levels were low, ranging from 8 to 205 μg/L, ensuring product safety. Analysis of volatile compounds identified 80 substances, including 16 key aroma-active compounds, contributing to a complex flavour profile. These results provide a basis for selecting R. arrhizus strains to optimise rice wine fermentation, addressing market demand for diverse and functional products.

Interactions of Saccharomyces cerevisiae and Lactiplantibacillus plantarum Isolated from Light-Flavor Jiupei at Various Fermentation Temperatures

Chinese Baijiu is a famous fermented alcoholic beverage in China. Interactions between key microorganisms, i.e., Saccharomyces cerevisiae and Lactiplantibacillus plantarum, have recently been reported at specific temperatures. However, empirical evidence of their interactions at various temperatures during fermentation is lacking. The results of this study demonstrated that S. cerevisiae significantly suppressed the viability and lactic acid yield of L. plantarum when they were cocultured above 15 °C. On the other hand, L. plantarum had no pronounced effect on the growth and ethanol yield of S. cerevisiae in coculture systems. S. cerevisiae was the main reducing sugar consumer. Inhibition of lactic acid production was also observed when elevated cell density of L. plantarum was introduced into the coculture system. A proteomic analysis indicated that the enzymes involved in glycolysis, lactate dehydrogenase, and proteins related to phosphoribosyl diphosphate, ribosome, and aminoacyl-tRNA biosynthesis in L. plantarum were less abundant in the coculture system. Collectively, our data demonstrated the antagonistic effect of S. cerevisiae on L. plantarum and provided insights for effective process management in light-flavor Baijiu fermentation.

Metaproteomic investigation of enzyme profile in daqu used for the production of Nongxiangxing baijiu

Enzymes and microbiota in daqu are essential for the brewing of Nongxiangxing baijiu. Uncover the key enzymes and functional strains in daqu is beneficial to improve the flavor and quality of Nongxiangxing baijiu. In this study, metaproteome technology was employed to determine the enzyme profiles in Nongxiangxing daqu, and strains with high saccharification activity were screened and identified. 933 proteins were identified in daqu, of which 463 belonged to enzymes, including 140 oxidoreductases, 98 transferases, 91 hydrolases, 49 ligases, 41 lyases and 27 isomerases, and hydrolase is the enzyme with the highest abundance in baijiu brewing. Among hydrolases, a total of 36 carbohydrate metabolism-related enzymes (CMEs) were identified, and 12 of them were key enzymes related to glycoside hydrolysis. Four major glycoside hydrolysis enzymes glucoamylase (EC 3.2.1.3), glucan 1,4-alpha-glucosidase (EC 3.2.1.3), glucanase (EC 3.2.1.-) and β-glucosidase (EC 3.2.1.21) were revealed, and their sources were Byssochlamys spectabilis, Lichtheimia ramosa and Thermoascus aurantiacus, respectively. Then, strains Aspergillus A2, A3, A7, Lichtheimia L1, L4, L5, and Saccharomycopsis S2, S4, S6 with high saccharifying enzyme-producing capacity were screened through culture-dependent approach. Resents presented in this study can further reveal the enzyme profiles and identify the main functional strains in daqu, which can provide theoretical support for the brewing of Nongxiangxing baijiu.