Metagenomics reveals the differences in flavor quality of rice wines with Hongqu and Maiqu as the fermentation starters

Chinese rice wine (CRW) is an alcoholic beverage made mainly from rice or grain through saccharification and fermentation with Jiuqu (starter). Jiuqu makes an important contribution to the formation of the flavor characteristics of rice wine. Hongqu and Maiqu are two kinds of Jiuqu commonly used in CRW brewing. This study compared the microbial community, biogenic amines (BAs), and volatile flavor components (VFCs) of two types of rice wine brewed with Hongqu and Maiqu as fermentation agents. The results showed that the amino acid content of rice wine fermented with Maiqu (MQW) was significantly lower than that of rice wine fermented with Hongqu (HQW). On the contrary, the majority of BAs in MQW were significantly higher than those in HQW, except for putrescine. Multivariate statistical analysis indicated that most of the VFCs detected were enriched in HQW, while ethyl 3-phenylpropanoate and citronellol were enriched in MQW. The results of metagenomic analysis showed that Weissiella, Enterobacter, Leuconostoc, Kosakonia, Saccharomyces, Aspergilus and Monascus were identified as the predominant microbial genera in HQW brewing process, while Saccharopolyspora, Lactococcus, Enterobacter, Leuconostoc, Kosakonia, Pediococcus, Pantoea, Saccharomyces, Aspergillus, Lichtheimia and Nakaseomyces were the predominant microbial genera in MQW brewing. In addition, some VFCs and BAs were strongly correlated with dominant microbial genera in HQW and MQW brewing. Bioinformatics analysis showed that the abundance of genes involved in BAs synthesis in MQW brewing was much higher than that in HQW brewing, while the abundances of genes related to metabolic pathway of characteristic VFCs in HQW brewing were obviously higher than those in MQW, which explained the differences in flavor quality between HQW and MQW from the perspective of microbial genes. Collectively, these findings provide scientific evidence for elucidating the contribution of different microbial genera to the formation of flavor quality of CRW, and is helpful for screening beneficial microbes to enhance flavor quality and drinking comfort of CRW.

Role of bacterial community succession in flavor formation during Sichuan sun vinegar grain (Cupei) fermentation

Sichuan sun vinegar (SSV) is a traditional Chinese vinegar with a unique flavor and it is fermented with bran as the main raw material. In the present study, we explored the bacterial community succession in fermented grains (Cupei) during SSV production. High-throughput sequencing results showed that bacterial community richness and diversity peaked on day 7 of fermentation. Lactobacillus and Acetobacter were the dominant bacteria throughout the fermentation process. However, Acetobacter, Cupriavidus, Sphingomonas, Pelomonas, and Lactobacillus were the most abundant genera in the late phase of fermentation on day 17. The boundaries of trilateral co-fermentation were determined through cluster analysis. Days 1-3 were considered the early fermentation stage (starch saccharification), days 5-11 were the middle fermentation stage (alcoholic fermentation), and days 13-17 represented the late fermentation stage (acetic acid fermentation). Changes in flavor compounds during Cupei fermentation were subsequently analyzed and a total of 86 volatile compounds, 9 organic acids, and 17 amino acids were detected. Although acetic acid, lactic acid, alcohols, and esters were the main metabolites, butyrate was also detected. Correlation analysis indicated that 20, 21, and 28 microorganisms were positively correlated with the abundance of amino acids, organic acids, and volatile flavor compounds, respectively. We further explored the microbial and metabolic mechanisms associated with the dominant volatile flavor compounds during SSV fermentation. Collectively, the findings of the current study provide detailed insights regarding the fermentation mechanisms of SSV, which may prove relevant for producing high-quality fermented products.

Comparative evaluation of the microbial diversity and metabolite profiles of Japanese-style and Cantonese-style soy sauce fermentation

Microorganisms play essential roles in flavor formation during soy sauce fermentation. Different soy sauce fermentation types significantly affect flavor formation. However, comparisons of microbial communities and metabolites between different fermentation types have been little studied. Here, we investigated variation in microbial communities, metabolite profiles, and metabolic pathways during Japanese-type (JP) and Cantonese-type (CP) fermentation. Free amino acids and volatile compound profiles varied significantly between fermentation types, with JP samples containing higher contents of esters (39.84%; p < 0.05), alcohols (44.70%; p < 0.05) in the 120 d fermentation samples. Volatile compound profiles varied significantly between fermentation types, with JP samples containing higher contents of esters, alcohols, and free amino acids (p < 0.05). Metagenomic analysis indicated that both JP and CP communities were dominated by Tetragenococcus, Staphylococcus, Weissella (bacteria), and Aspergillus (fungi), but the two communities varied differently over time. Tetragenococcus drastically increased in abundance throughout the fermentation (from 0.02 to 59.2%) in JP fermentation, whereas Tetragenococcus (36.7%) and Staphylococcus (29.7%) dominated at 120 d of fermentation in CP fermentation. Metagenomic functional profiles revealed that the abundances of most genes involved with carbohydrate, amino acid, and lipid metabolism exhibited significant differences between fermentation types (p < 0.05) during the middle to late fermentation stages. Furthermore, predicted metabolic pathways for volatile substance biosynthesis differed between JP and CP fermentation, likely explaining the differences in flavor metabolite profiles. In addition, most of the genes associated with flavor generation were affiliated with Tetragenococcus, Weissella, Staphylococcus, Bacillus, and Aspergillus, suggesting that these microbes play important roles in flavor production during soy sauce fermentation. This study significantly improves our understanding of microbial functions and their metabolic roles in flavor formation during different soy sauce fermentation processes.

Metagenomics-based insights into the microbial community profiling and flavor development potentiality of baijiu Daqu and huangjiu wheat Qu

Daqu and wheat Qu are saccharification and fermenting agents in Chinese huangjiu and baijiu production. This study aimed to investigate the difference between Daqu and wheat Qu in physicochemical indices, microbial communities, functional genes, and the metabolic network of key microbes responsible for flavor synthesis by whole-metagenome sequencing and metabolite analysis. Herein, physicochemical indices indicated that compared with wheat Qu, Daqu exhibited higher protease and cellulase activity and acidity, and lower glucoamylase and amylase enzyme activity. Metagenomic sequencing reveals that although Daqu and wheat Qu community composition have significant differences at species level, they have similar functional genes. Daqu were enriched in Pediococcus pentosaceus, Weissella paramesenteroides, Rasamsonia emersonii and Byssochlamys spectabilis (22.48% of the total abundance), while wheat Qu harbored greater abundances of Saccharopolyspora (54.78%, Saccharopolyspora rectivirgula, Saccharopolyspora shandongensis, Saccharopolyspora hirsuta, Saccharopolyspora spinose, and Saccharopolyspora erythraea). From a functional perspective, the important functions of Daqu and wheat Qu are both amino acid metabolism and carbohydrate metabolism. Meanwhile, a combined analysis among microbiota, functional genes, and dominant flavors indicated S. shandongensis, S. rectivirgula, and S. spinose might be the main contributor to the synthesis of flavor compounds in wheat Qu, while R. emersonii, W. paramesenteroides, Leuconostoc citreum, Leuconostoc mesenteroides, Weissella cibaria and P. pentosaceus may make the greatest contribution to flavor compounds synthesis in Daqu. This study reveals the microbial and functional dissimilarities of Daqu and wheat Qu, and helps elucidating different metabolic roles of microbes during flavor formation.

Aspergillus oryzae FaeA is responsible for the release of ferulic acid, a precursor of off-odor 4-vinylguaiacol in sake brewing

4-Vinylguaiacol (4-VG) is one of the most common off-flavors found in sake. 4-VG is produced from its precursor, ferulic acid, which is a component of the cell wall of the rice endosperm. The release of ferulic acid in sake brewing is thought to be mediated by feruloyl esterase produced by either Aspergillus oryzae or Saccharomyces cerevisiae. To investigate the effect of FaeA, a feruloyl esterase produced by A. oryzae, its loss-of-function strain was produced by genome co-editing. The feruloyl esterase activity of the faeA-deficient strain was drastically reduced. Sake was fermented using koji with S. cerevisiae strain G046, which can convert ferulic acid to 4-VG. Fermented sake was analyzed by measuring the 4-VG content and sensory evaluation. 4-VG content was reduced to approximately 10% of that of sake fermented with control koji. Sensory evaluation revealed that 4-VG was almost undetectable. Our findings showed that disruption of faeA in A. oryzae is a promising strategy to reduce 4-VG off-flavors in sake.

Enzyme Production Potential of Penicillium oxalicum M1816 and Its Application in Ferulic Acid Production

The present study focused on isolating an efficient enzyme production microorganism for ferulic acid (FA) production from wheat bran. A wild-type cellulase-, xylanase-, and feruloyl esterase-producing strain was isolated and identified as Penicillium oxalicum M1816. The genome was sequenced and assembled into 30.5 Mb containing 8301 predicted protein-coding genes. In total, 553 genes were associated with carbohydrate metabolism. Genomic CAZymes analysis indicated that P. oxalicum M1816, comprising 39 cellulolytic enzymes and 111 hemicellulases (including 5 feruloyl esterase genes), may play a vital role in wheat bran degradation and FA production. The crude enzyme of strain M1816 could release 1.85 ± 0.08 mg·g-1 FA from de-starched wheat bran (DSWB) at 12 h, which was significantly higher than other commercial enzymes. Meanwhile, when the strain M1816 was cultured in medium supplemented with DSWB, up to 92.89% of the total alkali-extractable FA was released. The process parameters of solid-state fermentation were optimized to enhance enzyme production. The optimized wheat bran Qu of P. oxalicum M1816 was applied to huangjiu fermentation, and the FA content was increased 12.4-fold compared to the control group. These results suggest that P. oxalicum M1816 is a good candidate for the development of fermented foods bio-fortified with FA.

The impact of different Saccharomyces cerevisiae strains on microbial composition and quality of Chinese rice wine fermentations

Chinese rice wine (CRW) is a popular fermented product in China, with complicated microbial composition and flavour compounds. To reveal the effects of different strains of Saccharomyces cerevisiae (N85 and XZ11) on the microbial composition in the process of brewing, metagenomic sequencing approaches were carried out to explore the dynamic changes of bacteria and fungi. Furthermore, the volatile compounds and organic acids in CRW were identified by headspace solid phase microextraction (HS-SPME)/gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) at the end of the brewing. Our results indicated that different S. cerevisiae strains could influence microbial compositions and especially affected the growth of Lactobacillus brevis and Pantoea ananatis. The changes in the microbial community structure contributed to the remarkable difference in the content of lactic acid, esters, alcohols, and aldehydes. Moreover, functional network analysis provided insights into the biological correlations between microbial species and metabolic pathways, that is, Lactobacillus genus had negative effects on metabolic activities. This study expands the idea of improving the quality of CRW by controlling the microbiome.

Microbial Community Structure and Chemical Constituents in Shinkiku, a Fermented Crude Drug Used in Kampo Medicine

Shinkiku (Massa Medicata Fermentata) is a traditional crude drug used to treat anorexia and dyspepsia of elder patients in east Asia. Shinkiku is generally prepared by the microbial fermentation of wheat and herbs. Shinkiku is also used in Japanese Kampo medicine as a component of (Hangebyakujutsutemmato). However, the quality of shinkiku varies by manufacture because there are no reference standards to control the quality of medicinal shinkiku. Thus, we aim to characterize the quality of various commercially available shinkiku by chemical and microbial analysis. We collected 13 shinkiku products manufactured in China and Korea and investigated the microbial structure and chemical constituents. Amplicon sequence analysis revealed that Aspergillus sp. was common microorganism in shinkiku products. Digestive enzymes (α-amylase, protease, and lipase), organic acids (ferulic acid, citric acid, lactic acid, and acetic acid), and 39 volatile compounds were commonly found in shinkiku products. Although there were some commonalities in shinkiku products, microbial and chemical characteristic considerably differed as per the manufacturer. Aspergillus sp. was predominant in Korean products, and Korean products showed higher enzyme activities than Chinese products. Meanwhile, Bacillus sp. was commonly detected in Chinese shinkiku, and ferulic acid was higher in Chinese products. Principal component analysis based on the GC-MS peak area of the volatiles also clearly distinguished shinkiku products manufactured in China from those in Korea. Chinese products contained higher amounts of benzaldehyde and anethole than Korean ones. Korean products were further separated into two groups: one with relatively higher linalool and terpinen-4-ol and another with higher hexanoic acid and 1-octen-3-ol. Thus, our study revealed the commonality and diversity of commercial shinkiku products, in which the commonalities can possibly be the reference standard for quality control of shinkiku, and the diversity suggested the importance of microbial management to stabilize the quality of shinkiku.

Improvement of the aroma of lily rice wine by using aroma-producing yeast strain Wickerhamomyces anomalus HN006

A fruity aroma-producing yeast strain was isolated with the aim of improving the aroma of fermented lily rice wine, and identified as Wickerhamomyces anomalus HN006. In addition, the effects of adding solid residues of previous fermentation cycles, and of fungus α-amylase and W. anomalus HN006 supplementation on the biochemical parameters of lily rice wine were evaluated. The optimum quality of the wine, in terms of ethanol and residual sugar content, acidity levels and aroma, was obtained with 5% (w/v) solid residue addition, and supplementation with 10 U/g fungal α-amylase and 2% (v/v) W. anomalus inoculum on the 4th day of fermentation. Volatile compound profiles, the total amount of amino acids and the sensory characteristics of the lily rice wines produced by the two fermentation processes were also evaluated and compared. The lily rice wine obtained from our optimized experimental technology produced higher amounts of some esters, free fatty acids, alcohols, aldehydes, ketones, alkenes, volatile phenol and thiazole, in addition to higher total amino acid content and sensory scores compared to the traditionally brewed wine. Our process resulted in an intensification and improvement of lily rice wine aroma.

Characterization of the Key Aroma Compounds in Aged Chinese Rice Wine by Comparative Aroma Extract Dilution Analysis, Quantitative Measurements, Aroma Recombination, and Omission Studies

The aroma compounds in young and aged Chinese rice wines (rice wines) with a clear difference in their overall aroma profiles were analyzed by comparative aroma extract dilution analysis (cAEDA). In AEDA, more aroma-active regions with flavor dilution (FD) factors of ≥64 were detected in the aged rice wine than in the young rice wine. A total of 43 odorants were further identified and quantitated. The odor activity values (OAVs) revealed 33 aroma compounds with OAVs of ≥1 in young or aged rice wine. Among these aroma compounds with relatively higher OAVs, 3-methylbutanoic acid, 1,1-diethoxyethane, vanillin, 3-methylbutanal, sotolon, benzaldehyde, 4-vinylguaiacol, methional, and 2,3-butanedione showed significant differences between young and aged rice wines. This difference was confirmed through a quantitative analysis of 34 rice wine samples with ages of 0-15 years. Then, the aroma profile of the aged rice wine was successfully simulated through an aroma recombination model. Omission models suggested that sotolon, vanillin, 3-methylbutanal, and benzaldehyde played key roles in the overall aroma of aged rice wine.

Polyphenols extracted from huangjiu have anti-inflammatory activity in lipopolysaccharide stimulated RAW264.7 cells

In the present study, an extraction method, combining extraction by ethyl acetate + ethanol and purification by HPD400 resin, was established to obtain huangjiu polyphenol extract (HPE). After extraction and purification, the polyphenol yield was 22.57%, and 90.57% protein and 97.99% sugar were removed. HPLC analysis indicated that (+)-catechin (91.33 μg mL-1) was the predominant phenolic compound among the 11 detected polyphenols. In LPS-stimulated RAW264.7 cells, HPE exhibits anti-inflammatory effects by inhibiting the production of NO and pro-inflammatory cytokines (TNF-α, interleukin IL-6 and IL-1β). The anti-inflammatory effect of HPE is associated with the inhibition of iNOS expression, the suppression of NF-κB translocation to the nucleus, and the inhibition of the phosphorylation of IκB and the MAPK family proteins, e.g. p-38, Erk 1/2, and JNK. Moreover, the activation of Nrf2 and HO-1 is also related to the anti-inflammatory effect of HPE.

Formation of Guaiacol by Spoilage Bacteria from Vanillic Acid, a Product of Rice Koji Cultivation, in Japanese Sake Brewing

The formation of guaiacol, a potent phenolic off-odor compound in the Japanese sake brewing process, was investigated. Eight rice koji samples were analyzed, and one contained guaiacol and 4-vinylguaiacol (4-VG) at extraordinarily high levels: 374 and 2433 μg/kg dry mass koji, respectively. All samples contained ferulic and vanillic acids at concentrations of mg/kg dry mass koji. Guaiacol forming microorganisms were isolated from four rice koji samples. They were identified as Bacillus subtilis, B. amyloliquefaciens/subtilis, and Staphylococcus gallinarum using 16S rRNA gene sequence. These spoilage bacteria convert vanillic acid to guaiacol and ferulic acid to 4-VG. However, they convert very little ferulic acid or 4-VG to guaiacol. Nine strains of koji fungi tested produced vanillic acid at the mg/kg dry mass koji level after cultivation. These results indicated that spoilage bacteria form guaiacol from vanillic acid, which is a product of koji cultivation in the sake brewing process.

Nature's chemical signatures in human olfaction: a foodborne perspective for future biotechnology

The biocatalytic production of flavor naturals that determine chemosensory percepts of foods and beverages is an ever challenging target for academic and industrial research. Advances in chemical trace analysis and post-genomic progress at the chemistry-biology interface revealed odor qualities of nature's chemosensory entities to be defined by odorant-induced olfactory receptor activity patterns. Beyond traditional views, this review and meta-analysis now shows characteristic ratios of only about 3 to 40 genuine key odorants for each food, from a group of about 230 out of circa 10 000 food volatiles. This suggests the foodborn stimulus space has co-evolved with, and roughly match our circa 400 olfactory receptors as best natural agonists. This perspective gives insight into nature's chemical signatures of smell, provides the chemical odor codes of more than 220 food samples, and beyond addresses industrial implications for producing recombinants that fully reconstruct the natural odor signatures for use in flavors and fragrances, fully immersive interactive virtual environments, or humanoid bioelectronic noses.