Exploring core functional microbiota responsible for the production of volatile flavour during the traditional brewing of Wuyi Hong Qu glutinous rice wine.

The objective of this study was to explore the core functional microbiota for the production of volatile flavour during the traditional brewing of Wuyi Hong Qu glutinous rice wine, one of the most typical representatives of rice wine in China. Microbiological analysis based on high-throughput sequencing (HTS) technology demonstrated that bacteria of Lactobacillus, Bacillus, Leuconostoc, Lactococcus, Raoultella, Staphylococcus, Pediococcus, and Weissella, and fungi of Saccharomyces, Saccharomycopsis, Rhizopus, Monascus, Pichia, Wickerhamomyces, Candida, and Aspergillus were the predominant genera during the traditional fermentation process. Principal component analysis (PCA) based on the relative abundance showed that both of bacterial and fungal communities varied significantly in different fermentation phases. Some predominant microbial species or genera (including bacteria of Bacillus spp., Staphylococcus spp., Weissella spp., and P. acidilactici, and fungi of M. purpureus, R. oryzae, R. arrhizus var. arrhizus, and A. niger) were detected at the initial brewing stage, and their populations decreased as the fermentation progressed, while those of Lactobacillus, Gluconacetobacter, Leuconostoc, Pichia, Wickerhamomyces, and Saccharomyces increased to become the predominant genera at the final stage. A total of 79 volatile compounds were identified in traditional fermentation starters and during the traditional brewing process, mainly including esters, alcohols, acids, aldehydes, ketones, and phenols. Heatmaps and PCA also revealed the significant variances in the composition of volatile compounds among different samples. Furthermore, the potential correlations between microbiota succession and volatile flavour dynamics were explored through bidirectional orthogonal partial least squares (O2PLS) based correlation analysis. Three bacterial genera, namely, Gluconacetobacter, Lactobacillus, Lactococcus, and three fungal genera of Pichia, Wickerhamomyces, and Saccharomyces, were determined as the core functional microbiota for production of main volatile compounds in Wuyi Hong Qu glutinous rice wine. To conclude, information provided by this study is valuable to the development of effective strategies for the selection of beneficial bacterial and fungal strains to improve the quality of Wuyi Hong Qu glutinous rice wine.

Comparative Transcriptomic and Metabolomic Analyses Reveal the Regulatory Effect and Mechanism of Tea Extracts on the Biosynthesis of Monascus Pigments.

Monascus pigments (MPs) are natural edible pigments with high safety and strong function, which have been widely used in food and health products. In this study, different types of tea extracts (rich in polyphenols) were used to regulate the biosynthesis of MPs. The results showed that 15% ethanol extract of pu-erh tea (T11) could significantly increase MPs production in liquid fermentation of Monaco's purpureus M3. Comparative transcriptomic and metabolomic analyses combined with reverse transcription-quantitative polymerase chain reaction (RT-qPCR) were used to further explore the regulatory mechanism of T11 on the biosynthesis of MPs. Comparative transcriptomic analysis showed that there were 1503 differentially expressed genes (DEGs) between the Con group and the T11 group, which were mainly distributed in carbohydrate metabolism, amino acid metabolism, energy metabolism, lipid metabolism, metabolism of terpenoids and polyketides, etc. A total of 115 differential metabolites (DMs) identified by metabolomics between the Con and T11 groups were mainly enriched in glutathione metabolism, starch and sucrose metabolism, alanine, aspartic acid and glutamate metabolism and glycine, serine and threonine metabolism, etc. The results of metabolomics were basically consistent with those of gene transcriptomics, indicating that the regulatory effect of T11 on the biosynthesis of MPs is mainly achieved through affecting the primary metabolic pathway, providing sufficient energy and more biosynthetic precursors for secondary metabolism. In this study, tea extracts with low economic value and easy access were used as promoters of MPs biosynthesis, which may be conducive to the application of MPs in large-scale industrial production. At the same time, a more systematic understanding of the molecular regulatory mechanism of Monascus metabolism was obtained through multi-omics analysis.

Comparative transcriptomic analysis reveals the regulatory effects of inorganic nitrogen on the biosynthesis of Monascus pigments and citrinin.

Monascus spp. and its secondary metabolites have been widely applied in foods and medicines for thousands of years in eastern Asia. Nitrogen sources are essential nutrients for the growth and metabolism of Monascus spp. Our previous study found that inorganic nitrogen sources (especially NH4Cl and NH4NO3) promoted the biosynthesis of Monascus pigments (MPs) and inhibited the production of citrinin. The objective of the present study was to investigate the regulatory mechanism of inorganic nitrogen on the biosynthesis of MPs and citrinin by the comparative transcriptional approach (RNA sequencing combined with RT-qPCR). Results indicated that the submerged fermentation of M. purpureus M3103 with NH4Cl or NH4NO3 as the sole nitrogen source can significantly increase the yields of MPs (especially for Monascus orange and red pigments) and decrease citrinin production, compared with the organic nitrogen source (peptone group). Comparative transcriptomic profiling by RNA sequencing found that the numbers of differentially expressed genes (DEGs) between different experimental groups-M group (peptone group) vs. ML group (NH4Cl group), and M group (peptone group) vs. MX group (NH4NO3 group), were 722 and 1287, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that genes involved in carbon and nitrogen metabolism, biosynthesis of amino acids were up-regulated by NH4Cl and NH4NO3, which would produce more biosynthetic precursors for MPs. Whereas, the inorganic nitrogen source (both of NH4Cl and NH4NO3) down-regulated the expression levels of genes involved in tyrosine metabolism. In addition, NR analysis indicated that the essential genes and transcription factors involved in the biosynthesis pathway of citrinin were down-regulated by NH4Cl and NH4NO3. These results indicated that NH4Cl or NH4NO3 as a nitrogen source for M. purpureus M3103 can significantly promote the precursor synthesis of Monascus pigments, but reduce the transcription of polyketide synthase for citrinin, and therefore significantly increase Monascus pigments production and decrease citrinin formation. These findings will facilitate a comprehensive understanding of the regulatory mechanisms of inorganic nitrogen in the biosynthesis of secondary metabolites in M. purpureus, and would benefit the application of M. purpureus in the production of MPs.

Hypoglycemic and hypolipidemic activities of Grifola frondosa polysaccharides and their relationships with the modulation of intestinal microflora in diabetic mice induced by high-fat diet and streptozotocin.

This study aimed to investigate the hypoglycemic and hypolipidemic activities of polysaccharides from Grifola frondosa (GFP) in diabetic mice induced by high-fat diet (HFD) and streptozotocin (STZ). Results showed that oral administration of GFP markedly reduced the serum levels of fasting blood glucose (FBG), oral glucose tolerance (OGT), cholesterol (TC), triglyceride (TG) and low-density lipoprotein cholesterol (LDL-C), and significantly decreased the hepatic levels of TC, TG and free fatty acids (FFA). Meanwhile, high-dose of GFP supplementation (900 mg/kg day) also showed powerful effects on moderating the composition of intestinal microflora in diabetic mice, especially altering the functionally relevant intestinal microbial phylotypes. Spearman's correlation network analysis revealed that key microbial phylotypes responding to GFP intervention were strongly correlated with the glucose and lipid metabolic disorders associated parameters. Moreover, GFP treatment regulated mRNA expression levels of the genes responsible for hepatic glucose and lipid metabolism. It is noteworthy that GFP treatment markedly increased mRNA expression of cholesterol 7α-hydroxylase (CYP7A1) and bile salt export pump (BSEP), suggesting an enhancement of bile acids (BAs) synthesis and excretion in liver. These findings demonstrated that GFP could prevent hyperglycemia and hyperlipidemia in diabetic mice by altering gut microbiota and regulating hepatic glycolipid metabolism related genes, and therefore could be used as potential functional food ingredients for the prevention or treatment of hyperglycemia and hyperlipidemia.

Preparation of a novel Grifola frondosa polysaccharide-chromium (III) complex and its hypoglycemic and hypolipidemic activities in high fat diet and streptozotocin-induced diabetic mice.

Polysaccharide from Grifola frondosa is one of the best metal-ion chelating agents because of its structural characteristics and excellent functional activities. In this study, we synthesized and characterized a novel Grifola frondosa polysaccharide-chromium (III) [GFP-Cr(III)] complex. Response surface methodology (RSM) was used to optimize the reaction conditions for the maximum chelation rate of GFP-Cr(III) complex. The optimal reaction conditions obtained from RSM were as follows: concentration of CrCl3 6.97 mg/mL, pH 7.75 and temperature 71.73 °C, respectively. The pH was the most significant factor, followed by reaction temperature and concentration of CrCl3. Under the deduced optimal conditions (CrCl3 7.0 mg/mL, pH 7.7 and temperature 70.0 °C), the experimental chelation rate was 28.01% ±â€¯0.18% for GFP-Cr(III) complex, which agreed closely with the predicted value (27.61%). Fourier transform infrared (FTIR) spectroscopy revealed that the primary sites of chromium (III)-binding in polysaccharides were OH and CN groups, leading to the structure of GFP-Cr(III) complex was loose than the original polysaccharide. Nevertheless, Cr(III) did not make a fundamental change in the structure of GFP when comparing the FTIR spectra of GFP and GFP-Cr(III) complex. Additionally, the effects of GFP-Cr(III) complex on hyperglycemia and hyperlipidemia in high-fat diet (HFD) and streptozotocin (STZ)-induced diabetic mice were also investigated. Results showed that the serum total cholesterol (TC), total triglyceride (TG), low density lipoprotein cholesterol (LDL-C), fasting blood glucose levels and glucose tolerance in diabetic mice fed a high-fat diet (HFD) supplemented with GFP-Cr(III) complex (900 mg/kg day) were significantly lower than the diabetic group (P < 0.01). These results suggest that GFP-Cr(III) complex could be used as potential functional food ingredients for the prevention or treatment of hyperglycemia and hyperlipidemia.

Microbial communities and volatile metabolites in different traditional fermentation starters used for Hong Qu glutinous rice wine.

Hong Qu glutinous rice wine (HQGRW), as one of the most typical representatives of Chinese rice wine, is generally brewed from glutinous rice by adding two traditional wine fermentation starters-Hong Qu (HQ) and Bai Qu (BQ). The objective of this study was to determine the microbial communities and volatile metabolites of different traditional fermentation starters for HQGRW, and elucidate the potential correlation between microbiota and volatile metabolites. Both heatmap and principal component analysis (PCA) revealed the significant variances in volatile profiles among different wine starters. Microbiological analysis based on high-throughput sequencing (HTS) technology demonstrated that both of bacterial and fungal communities varied significantly in different starters. HQ was dominated mainly by bacteria of Bacillus ginsengihumi (20.17%), Pantoea sp. (10.39%), Elizabethkingia sp. (5.52%), Streptococcus sp. (5.03%) Brevundimonas sp. (3.03%), Rickettsia prowazekii (2.94%), Thermus thermophilus (2.54%), Bacillus amyloliquefaciens (1.48%), Bacillus aryabhattai (1.42%); fungi of Monascus purpureus (39.7%), Aspergillus niger (27.35%), Xeromyces bisporus (8.39%), Aspergillus penicillioides (6.89%), Aspergillus flavus (2.33%) and Pichia farinose (0.79%). By contrast, BQ contained much higher proportions of bacteria of Lactococcus lactis (10.45%), Lactobacillus brevis (9.99%), Pediococcus pentosaceus (8.29%), Weissella paramesenteroides (6.69%), Lactobacillus fermentum (4.83%), Gluconobacter thailandicus (3.93%), Lactobacillus alimentarius (3.59%), fungi of Rhizopus arrhizus (31.47%), Saccharomycopsis fibuligera (27.86%), Aspergillus niger (20.81%), Issatchenkia orientalis (3.79%), Saccharomycopsis malanga (3.15%), Clavispora lusitaniae (2.29%), Candida tropicalis (1.47%), Saccharomyces cerevisiae (1.11%) and Rhizopus microsporus (0.57%). Furthermore, core functional microbiota that might contribute to volatile flavour development was explored through Spearman's correlation-based network analysis. Lactobacillus brevis, Lactobacillus alimentarius, Lactobacillus plantarum and Aspergillus niger were found to be strongly associated with acid compounds (FDR adjusted P < 0.01), while Pichia sp., Candida sp., Monascus purpureus, Lactobacillus brevis and Lactobacillus alimentarius were positively correlated with concentrations of aromatic esters associated with fruity and floral notes (FDR adjusted P < 0.01), implying that these microorganisms might make significant contributions to the flavour of rice wine. These findings demonstrated that the aromatic quality of HQGRW may be critically influenced by the microbiota in traditional fermentation starters. To conclude, this study would contribute to the development of novel defined starter cultures for improving the aromatic quality of HQGRW.

The regulation mechanisms of soluble starch and glycerol for production of azaphilone pigments in Monascus purpureus FAFU618 as revealed by comparative proteomic and transcriptional analyses.

Monascus spp. have been used for thousands of years as a traditional food additive in China. This mold can produce many different types of commercially valuable secondary metabolites of biological activity. Soluble starch and glycerol are the two principal carbon sources universally utilized by Monascus for the production of beneficial metabolites. In this study, the effects and regulation mechanisms of soluble starch and glycerol for M. purpureus FAFU618 on Monascus azaphilone pigments (MonAzPs) were investigated through ultra-performance liquid chromatography quadrupole time of flight mass spectrometry (UPLC-QTOF-MS/MS), comparative proteomics and quantitative real-time reverse transcription polymerase chain reaction (RT-qPCR). The production of intracellular and extracellular pigments was significantly different between the soluble starch group (SSG) and glycerol group (GCG). Additionally, the components of intracellular pigments revealed by UPLC-QTOF-MS/MS showed that Monascin and Ankaflavin increased significantly in the GCG, while Rubropunctatin and Monascorubrin increased in the SSG. Differentially expressed proteins of mycelia between SSG and GCG were analyzed by two-dimensional gel electrophoresis (2-DE) and MALDI-TOF/TOF MS. We identified 27 proteins with statistically altered expression, of which 18 proteins associated with the EMP (glycolytic pathway), translation, energy generation, proteolysis, etc. were up-regulated, and 9 proteins, including ribosomal proteins, heat shock proteins (HSPs) and others, were down-regulated in GCG. Meanwhile, the expression levels of MonAzP biosynthetic genes were also analyzed by RT-qPCR, and the results showed that mppA, mppC, mppR1 and mppR2 were down-regulated, whereas genes MpPKS5, MpFasA2, MpFasB2, mppB, mppD and mppE were up-regulated. Collectively, these findings illustrate that the regulation of MonAzPs is not only closely related to the expression levels of certain proteins in the polyketide synthesis pathway but also closely related to the concentration of primary metabolism-generated molecules that are used as substrates for polyketide synthesis. The present study provides insights into the regulation of different carbon sources on the metabolism of MonAzPs in M. purpureus FAFU618. These results may promote further development of functional foods or medicines from Monascus spp. fermented products.