Depth-depended quality comparison of light-flavor fermented grains from two fermentation rounds

Effect of mixed fermentation of compound grapes on organic acids and volatiles in mulberry wine

The main objective of this study was to investigate the effect of mixed fermentation of blended grapes on the organic acid and volatile content of mulberry fruit wines before and after fermentation. Rose-scented grapes and blackberry grapes were chosen to produce fruit wines through mixed fermentation with mulberries, respectively. HPLC was employed for the content of organic acids, whereas the concentrations of volatile compounds in the mulberry wines were determined using HS-SPME-GC-MS. The results showed that yeast fermentation could effectively reduce the content of malic acid and citric acid while generating rich aroma substances. During compound grape blend fermentation, the organic acid content decreases, and more volatile compounds are produced. Among them, mulberry rosé grapefruit wine exhibits a more complex array of volatile compounds, including phenylethanol, ethyl caprylate, and ethyl caprate, alongside recently discovered compounds like isobutanol, (+)-3-methyl-2-butanol, and α-pinitol. These compounds contribute to the enhanced flavor of mulberry wine.

Identification of the saccharifying microbiota based on the absolute quantitative analysis in the batch solid-state fermentation system

The fermentation process of Chinese baijiu, a distinctive example of batch solid-state fermentation (BSSF), involves the recurrent use of the same raw material to optimize starch utilization. However, it is unclear which microorganisms are able to metabolize low concentration starch effectively. In this study, we successfully identified the key saccharifying microbiota that degraded low-concentration starch in the BSSF system by absolute quantification techniques. The results indicated a 61.93 % enhancement in the efficient utilization of starch, absolute quantification combined with correlation analysis revealed that Geotrichum, Aspergillus, Bacillus, Candida, and Kroppenstedtia were the saccharifying microbiota, with relative abundances exceeding 10 % during fermentation. In the KEGG metabolic pathway, these five saccharifying microbiota had a complete metabolic pathway for degrading starch to d-glucose-1p and d-glucose, including eight related enzymes: maltose phosphorylase, α-amylase, glucoamylase, oligo-1,6-glucosidase, α-glucosidase, pullulanase, α-glucosidase, and maltogenic α-amylase. These studies showed that the saccharifying microbiota can co-degrade starch by multiple saccharifying enzymes, thus improving the utilization of starch substrates.

Evaluation of differences in volatile flavor compounds between liquid-state and solid-state fermented Tartary buckwheat by Monascus purpureus

The differences in volatile flavor compounds (VFCs) between Monascus-solid-state fermented Tartary buckwheat (MSFTB) and Monascus-liquid-state fermented Tartary buckwheat (MLFTB) were investigated using electronic nose and gas chromatography-ion mobility spectrometry (GC-IMS) analysis. The study revealed several significant differences in the composition and abundance of VFCs between the two states. Compared to MSFTB, MLFTB exhibited notable increases in various elements including protein, crude fat, total flavonoids, total polyphenols, Monacolin K, Monascus pigments. Principal component analysis demonstrated significant increases in the production of specific VFCs in MLFTB compared to MSFTB. A total of 25 VFCs were identified through GC-IMS, including 9 esters, 7 alcohols, 5 ketones, and 4 aldehydes. The content of pleasant VFCs in MLFTB was significantly higher than in MSFTB. These compounds served as both VFCs and key aroma components during fermentation. In conclusion, the Monascus fermentation state played a crucial role in enhancing the flavor quality of Tartary buckwheat.

Metagenomic and metabolomic profiling analyses to unravel the formation mechanism of n-propanol during the first and second round of Jiangxiangxing Baijiu fermentation

N-propanol is one of the higher alcohols, a moderate amount of n-propanol is beneficial for the harmony of the liquor body, whereas excessive or repeated intake will lead to discomfort and pose significant harm to human health. In actual production process of Jiangxiangxing Baijiu, the n-propanol content of the base baijiu in first round (FR) is far higher than that of second round (SR). Nevertheless, the formation mechanism and the key n-propanol producing microbials remain unclear and this limits the quality control of baijiu fermentation. Here, we combined metagenomics and metabolomics to verify the biosynthesis pathway of n-propanol and to identify characteristic microorganisms in FR and SR. The results showed that the preliminary period of pit fermentation was critical for the accumulation of n-propanol. FR was enriched in Lactobacillus plantarum, Lactobacillus ponits, Lactobacillus brevis and Lactobacillus panis, while it was harbored greater abundances of Pichia kudriazevii, Saccharomyces cerevisiae and Lactobacillus acetotolerans in SR. Function analysis combined with KEGG providing comprehensive evidence for the main synthetic pathways of n-propanol in Jiangxiangxing baijiu, and L. panis was key microbial. In addition, the experiments of inoculating L. panis and L. acetotolerans in situ indicated L. panis was mainly responsible for n-propanol production while L. acetotolerans not conducive to the production of n-propanol. Besides, the bioturbation effect on microbiota and flavor compounds were also analyzed. These results are useful for elucidating the mechanism of flavor formation in baijiu fermentation and promoting the further application of bioturbation technology in the traditional fermentation industry.

Differences in microbial communities among different types of zaopei and their effects on quality and flavor of baijiu

Three types of zaopei (fermented grain) of xiaoqu light-flavor baijiu (XQZP), daqu light-flavor baijiu (DQZP), and strong-flavor baijiu (SFZP) at the end of fermentation and their dominant lactic acid bacteria were systematically compared and analyzed in this study. The results showed that these three types of zaopei differed significantly in acidity, reducing sugar content, and ethanol content, and that the main factors influencing their microbial community were acidity and lactic acid. The diversity and contents of flavor substances were significantly higher in SFZP than in DQZP and XQZP. Additionally, there was a strong correlation between dominant lactic acid bacteria and flavor substances in all three zaopei, but the correlation between fungi and flavor substances was higher than that between bacteria and flavor substances. Differential gene analysis revealed that the microbial activities followed the order of SFZP > DQZP > XQZP. The KEGG enrichment analysis indicated that the differential genes from different zaopei were enriched in different metabolic pathways. Furthermore, various microorganisms in 3 types of zaopei contained different functional genes, of which fungi mainly contained genes responsible for the synthesis of ethanol and acetic acid, while lactic acid bacteria mainly contained genes responsible for the synthesis of lactic acid. In XQZP, L. helveticus was dominant lactic acid bacteria prominent in acetic acid tolerance and lactic acid production; in DQZP, L. acetotolerans was remarkable in its tolerance to lactic acid, acetic acid, ethanol and lactic acid production; and in SFZP, A. jinshanensis was superior in acetic acid tolerance and production. Taken together, this study reveals the mechanism underlying flavor differences among three types of baijiu and provides valuable references for the development and utilization of baijiu microbial resources.

Evaluation of the effect of Torulaspora delbrueckii on important volatile compounds in navel orange original brandy using E-nose combined with HS-SPME-GC-MS

Simultaneous inoculation of non-Saccharomyces cerevisiae during the alcoholic fermentation process has been found to be an effective strategy for enhancing wine flavor. This study aimed to investigate the effect of Torulaspora delbrueckii NCUF305.2 on the flavor of navel orange original brandy (NOOB) using E-nose combined with HS-SPME-GC-MS. The results showed a significant increase (p < 0.05) in the sensitivity of NOOB to W5C, W3C, W1S, and W3S sensors by mixed fermentation (MF). Esters in NOOB increased by 4.13%, while higher alcohols increased by 21.93% (p < 0.001), terpenes and others increased by 52.07% and 40.99% (p < 0.01), respectively. Notably, several important volatile compounds with relative odor activity values above 10 showed an increase. Sensory analysis revealed that a more pronounced citrus-like flavor and higher overall appearance scores were found in MF than in pure fermentation (PF). These findings offer valuable theoretical guidance for enhancing the quality of fruit brandies.

Strategies and Challenges of Microbiota Regulation in Baijiu Brewing

The traditional Chinese Baijiu brewing process utilizes natural inoculation and open fermentation. The microbial composition and abundance in the microecology of Baijiu brewing often exhibit unstable characteristics, which directly results in fluctuations in Baijiu quality. The microbiota plays a crucial role in determining the quality of Baijiu. Analyzing the driving effect of technology and raw materials on microorganisms. Elucidating the source of core microorganisms and interactions between microorganisms, and finally utilizing single or multiple microorganisms to regulate and intensify the Baijiu fermentation process is an important way to achieve high efficiency and stability in the production of Baijiu. This paper provides a systematic review of the composition and sources of microbiota at different brewing stages. It also analyzes the relationship between raw materials, brewing processes, and brewing microbiota, as well as the steps involved in the implementation of brewing microbiota regulation strategies. In addition, this paper considers the feasibility of using Baijiu flavor as a guide for Baijiu brewing regulation by synthesizing the microbiota, and the challenges involved. This paper is a guide for flavor regulation and quality assurance of Baijiu and also suggests new research directions for regulatory strategies for other fermented foods.

Exploring metabolic dynamics during the fermentation of sea buckthorn beverage: comparative analysis of volatile aroma compounds and non-volatile metabolites using GC-MS and UHPLC-MS

Sea buckthorn has a high nutritional value, but its sour taste and foul odor make it unpalatable for consumers. In this study, we analyzed the metabolite changes occurring during the yeast-assisted fermentation of sea buckthorn juice using the HeadSpace Solid-Phase Microextraction Gas Chromatography-Mass Spectrometry (HS-SPME-GC-MS) and Ultra-High Performance Liquid Chromatography-Mass Spectrometry (UHPLC-MS) techniques. A total of 86 volatile aroma compounds were identified during the fermentation process. The content of total volatiles in sea buckthorn juice increased by 3469.16 μg/L after 18 h of fermentation, with 22 compounds showing elevated levels. Notably, the total content of esters with fruity, floral, and sweet aromas increased by 1957.09 μg/L. We identified 379 non-volatile metabolites and observed significant increases in the relative abundance of key active ingredients during fermentation: glycerophosphorylcholine (increased by 1.54), glutathione (increased by 1.49), L-glutamic acid (increased by 2.46), and vanillin (increased by 0.19). KEGG pathway analysis revealed that amino acid metabolism and lipid metabolism were the primary metabolic pathways involved during fermentation by Saccharomyces cerevisiae. Fermentation has been shown to improve the flavor of sea buckthorn juice and increase the relative content of bioactive compounds. This study provides novel insights into the metabolic dynamics of sea buckthorn juice following yeast fermentation through metabolomics analysis. These findings could serve as a theoretical foundation for further studies on the factors influencing differences in yeast fermentation.

Response of microbiota to exogenous inoculation improved the enzymatic activities of medium-temperature Daqu

To explore the potential mechanism of improving enzymatic activities in medium-temperature Daqu (MTD) by inoculation functional isolates, we inoculated a single strain of Bacillus licheniformis, and the microbiota composed of Bacillus velezensis and Bacillus subtilis in MTD to investigate the association between the response of the functional microbiota and the enzymatic activity. The results showed that the bacterial community of MTD might be more sensitive to bioturbation than the fungal community, and the indigenous microbiota responded to the single strain more than to the microbiota. Moreover, the differential microorganisms mainly included Lactobacillales, Bacillales, and Saccharomycetales between the conventional and fortified samples. Notably, the composition of functional microbiota related to liquefying activity (LA) and saccharifying activity (SA) were significantly different, changing from Lactobacillus and Rhizomucor to Bacillus, Weissella, and Hyphopichia. That might be closely related to the effect of the bioturbation on LA (31.33%) and SA (43.54%) associated microorganisms was more tellingly. Furthermore, the relative abundance changes of bioturbation-sensitive modules in the co-occurrence network might also lead to the difference in enzymatic activities. Therefore, the LA and SA of MTD were improved by bioturbation significantly. These results provide diverse insights into the exogenous functional isolates to regulate the MTD microbiota and improve enzymatic activities.

Microbial characteristics and metabolite profiles of high-temperature Daqu in different maturation stages

The maturation period of high-temperature Daqu (HTD) is usually 3-6 months, and the characteristics of HTD at different maturation stages were different. In this study, the microbial characteristics and metabolite profiles of HTD at different maturation stages were revealed with the combination of physicochemical detection, the third generation Pacific Biosciences (PacBio) single-molecule, real-time (SMRT) sequencing technology, gas chromatography-mass spectrometry (GC-MS), and gas chromatography-ion mobility spectrometry (GC-IMS). Results showed that HTD matured for 6 months (Mix_m6) had higher saccharification power but less culturable thermotolerant bacteria and fungi than HTD matured for 3 months (Mix_m3). The average relative abundances of Thermoactinomyces, Paenibacillus, and Rasamsonia in Mix_m3 were higher than that in Mix_m6, while the average relative abundances of Bacillus, Pseudomonas, Thermoascus increased obviously with the prolongation of the maturation period. Streptomyces and Thermoactinomyces were biomarkers in Mix_m3, while Burkholderia and Pseudomonas were regarded as biomarkers in Mix_m6. Differences in microbiota structure led to different enrichment of metabolic pathways in HTD at different maturation stages, resulting in different flavor profiles, especially in ethyl acetate, 1-octen-3-one, (E)-3-Hexen-1, 2,3,5-trimethy-6-ethylpyrazine, pyrazine, tetramethyl content. The microbiota and metabolite characteristics of HTD comprehensively reflected the HTD quality in different maturation stages, which provided a reference for determining the optimal maturation time.