To enhance the aromas in Guangdong rice-flavor Baijiu, ester-producing yeast was selected to fortify Baijiu brewing. Among eight kinds of ester-producing yeasts selected, Saccharomyces cerevisiae CM15 (CM15) that showed both the stronger ability to utilize substrates to produce esters and the excellent tolerance to industrially relevant stress factors was chosen. When CM15 was synergistically fermented with six kinds of Kojis from distilleries of rice-flavor liquor in Guangdong, the enhanced total esters had happened to the liquors brewing with the fortified four kinds of Kojis, especially with Koji F. When Koji F was fortified with CM15, the resultant Baijiu showed a higher esters proportion and a lower higher alcohol ratio than that of Baijiu brewed only with Koji F, with the content of ethyl acetate and ethyl lactate increasing by 25% and 214%, respectively. This study suggested that CM15 can be used as a functional microorganism to fortify Baijiu brewing, which might also be suitable for other traditional fermented foods.

Higher alcohol, as an inevitable product of fermentation, plays an important role in the flavor and quality of Baijiu. However, the relationship between the complex microbial metabolism and the formation of higher alcohols in rice-flavor Baijiu was not clear. To investigate the relationship between microorganisms and higher alcohol production, two fermentation mashes inoculated with starters from Heyuan Jinhuangtian Liquor Co., Ltd. (Heyuan, China) as JM and Guangdong Changleshao Co., Ltd. (Meizhou, China) as CM, respectively, with significant differences in higher alcohol profiles during rice-flavor Baijiu fermentation were selected. In general, higher alcohols presented a rapid accumulation during the early fermentation stages, especially in JM, with higher and faster increases than those in CM. As for their precursors including amino acids, pyruvic acid and ketoacids, complex variations were observed during the fermentation. Metagenomic results indicated that Saccharomyces cerevisiae and Rhizopus microsporus were the microorganisms present throughout the brewing process in JM and CM, and the relative abundance of R. microsporus in JM was significantly higher than that in CM. The results of higher alcohol metabolism in JM may contribute to the regulation of higher alcohols in rice-flavor Baijiu.

Rice-flavor baijiu is a distilled Chinese spirit prepared from Xiaoqu culture. However, its dull taste may be a market limitation. In order to enhance the flavor profile of rice-flavor baijiu, two ester-producing yeast strains (Saccharomyces cerevisiae and Cyberlindnera fabianii) were inoculated for fermentation. At the end of the fermentation, the total alcohol and ester contents had also increased by 43.3% and 29.8%, respectively, and the number of ester species had increased by eight. Additionally, eleven flavor substances had significant contributions in the inoculated fermentation process, including several different esters and alcohols. A macrogenomic analysis revealed that the majority of the gene abundances associated with the alcohol, acid, and ester pathways were elevated by the third day of inoculated fermentation, and greater abundances of Saccharomyces cerevisiae, Cyberlindnera fabianii, Lichtheimia ramosa, Rhizopus delemar, and Rhizopus oryzaefive, annotated with these genes, were observed from either the pre-fermentation stage or post-fermentation stage. The results demonstrate that two added strains are associated with an increase in the content of the flavor substances. These findings may prove beneficial in enhancing the quality of rice-flavor baijiu through using inoculated fermentation with ester-producing yeast.

Lactobacillus amylolyticus L6, a gram-positive amylolytic bacterium isolated from naturally fermented tofu whey (NFTW), was able to hydrolyze raffinose and stachyose for the production of α-galactosidase. The cell-free extract of L. amylolyticus L6 was found to exhibit glycosyltransferase activity to synthesize α-galacto-oligosaccharides (GOS) with melibiose as substrate. The coding genes of α-galactosidase were identified in the genome of L. amylolyticus L6. The α-galactosidase (AglB) was placed into GH36 family by amino acid sequence alignments with other α-galactosidases from lactobacilli. The optimal reaction conditions of pH and temperature for AglB were pH 6.0 and 37°C, respectively. Besides, potassium ion was found to improve the activity of AglB while divalent mercury ion, copper ion and zinc ion displayed different degrees of inhibition effect. Under the optimum reaction condition, AglB could catalyze the synthesis of GOS with degree of polymerization (DP) ≥5 by using 300 mM melibiose concentration as substrate. The maximum yield of GOS with (DP) ≥3 could reach 31.56% (w/w). Transgalactosyl properties made AglB a potential candidate for application in the production of GOS.