No abstract

In this study, we used Chinese chestnut as the main raw material to develop a novel type of whiskey. First, 16 yeasts were isolated and identified for producing aroma using olfactory plate assay. Of these, we screened nine yeast strains based on their fermentation capacity, aroma profile, and sensory evaluation. The results demonstrated the combination of strains HN006 (Saccharomyces cerevisiae) and HN010 (Wickerhamomyces anomalus) provided satisfactory wine fermentation with an interesting flavor profile, as strain HN010 was highly aromatic and had elevated sensory scores with comparatively low ethanol yield, while strain HN006 had a poor flavor profile but produced the largest amount of ethanol. Subsequently, we co-cultured strains HN006 and HN010 to optimize the fermentation system. The results revealed the following optimum parameters: a mixed inoculum of 6% (v/v) at an HN006/HN010 ratio of 1:2 (v/v), a raw material ratio of 5:3:2 (chestnut: malt: glutinous rice), and yeast extract concentration of 6 g/L. Additionally, this fermentation system was successfully scaled-up to a 1000 L pilot-scale system. The results of this study showed that strains HN006 and HN010 could be used as alternatives for whiskey fermentation, as well as provided a generalized experimental scheme to assess other microorganisms.

In this study, the diversity of bacterial and fungal communities in the strong flavour Daqu production process was investigated using polymerase chain reaction denatured gradient gel electrophoresis (PCR-DGGE). The band number, dominance, diversity and similarity of the 16S rDNA differed in the DGGE patterns, reflecting the wide diversity of the microbial communities present in the different phases. The band abundance and dominance of the eukaryotic microbial community varied in the different phases. To provide insight into factors contributing to this diversity, the physicochemical properties of Daqu were explored. The core temperature of Daqu gradually increased to a maximum during the Dinghuo phase followed by a decline. The moisture and starch content decreased throughout fermentation. The total acid, reducing sugar, amino nitrogen, α-amylase activity, glucoamylase activity, protease activity, bacterial and mould number increased gradually to a maximum value at the end of the Peijun phase before decreasing in the Dinghuo phase increasing slightly in the Huanluo phase and then remaining almost unchanged. The esterase activity exhibited a similar change to that of other enzymes and then slightly increased after the Peijun stage. For yeasts, the highest number was obtained at the Peijun stage and then decreased. Correlation analysis revealed that the diversity of both bacteria and fungi was negatively correlated with moisture and starch and positively correlated with other indices. The reducing sugar, amino nitrogen, α-amylase and protease activities showed significant positive correlation with bacteria, and glucoamylase and esterase showed significant correlation with fungi.

Chinese strong-flavour liquor is produced via a traditional solid-state fermentation strategy facilitated by live microorganisms in pit mud-based cellars. For the present analysis, pit mud samples from different spatial locations within fermentation cellars were collected, and the yeast communities therein were assessed via culture-based and denaturing gradient gel electrophoresis (DGGE) approaches. These analyses revealed significant differences in the composition of yeast communities present in different layers of pit mud. In total, 29 different yeast species were detected, and principal component analyses revealed clear differences in microbial diversity in pit mud samples taken from different cellar locations. Culture-dependent strategies similarly detected 20 different yeast species in these samples. However, while Geotrichum silvicola, Torulaspora delbrueckii, Hanseniaspora uvarum, Saturnispora silvae, Issatchenkia orientalis, Candida mucifera, Kazachstania barnettii, Cyberlindnera jadinii, Hanseniaspora spp., Alternaria tenuissima, Cryptococcus laurentii, Metschnikowia spp., and Rhodotorula dairenensis were detected via a PCR-DGGE approach, they were not detectable in culture-dependent analyses. In contrast, culture-based approaches led to the identification of Schizosaccharomyces pombe and Debaryomyces hansenii in these pit mud samples, whereas they were not detected using DGGE fingerprints profiles. An additional HS-SPME-GC-MS-based analysis of the volatile compounds present in fermented grains samples led to the identification of 66 such compounds, with the highest levels of volatile acids, esters, and alcohols being detected in fermented grains from lower layer samples. A canonical correspondence analysis (CCA) suggested they were significant correlations between pit mud yeast communities and associated volatile compounds in fermented grains.

Chinese strong-flavour liquor is produced via a traditional solid-state fermentation strategy facilitated by live microorganisms in pit mud-based cellars. For the present analysis, pit mud samples from different spatial locations within fermentation cellars were collected, and the yeast communities therein were assessed via culture-based and denaturing gradient gel electrophoresis (DGGE) approaches. These analyses revealed significant differences in the composition of yeast communities present in different layers of pit mud. In total, 29 different yeast species were detected, and principal component analyses revealed clear differences in microbial diversity in pit mud samples taken from different cellar locations. Culture-dependent strategies similarly detected 20 different yeast species in these samples. However, while Geotrichum silvicola, Torulaspora delbrueckii, Hanseniaspora uvarum, Saturnispora silvae, Issatchenkia orientalis, Candida mucifera, Kazachstania barnettii, Cyberlindnera jadinii, Hanseniaspora spp., Alternaria tenuissima, Cryptococcus laurentii, Metschnikowia spp., and Rhodotorula dairenensis were detected via a PCR-DGGE approach, they were not detectable in culture-dependent analyses. In contrast, culture-based approaches led to the identification of Schizosaccharomyces pombe and Debaryomyces hansenii in these pit mud samples, whereas they were not detected using DGGE fingerprints profiles. An additional HS-SPME-GC-MS-based analysis of the volatile compounds present in fermented Zaopei samples led to the identification of 66 such compounds, with the highest levels of volatile acids, esters, and alcohols being detected in fermented Zaopei from lower layer samples. A canonical correspondence analysis (CCA) suggested they were significant correlations between pit mud yeast communities and associated volatile compounds in fermented Zaopei.