Flavor Metabolism Research Articles

Insight into flavor changes in bighead carp (Aristichthys nobilis) fillets during storage based on enzymatic, microbial, and metabolism analysis

The flavor alterations in bighead carp subjected to varying storage temperatures and the underlying metabolic mechanism were elucidated. Analysis of volatile flavor compounds, electronic nose, free amino acids, ATP-related compounds, and sensory evaluations uncovered a progressive flavor deterioration during storage, especially at 25 °C. Metabolomics-based flavor relating component profiling analysis showed that free fatty acids formed various fatty aldehydes including (E, E)-2,4-heptadienal and nonanal under lipoxygenase catalysis. Alcohol dehydrogenase and alcohol acyltransferases were intimately involved in alcohol and ester generation, while alkaline phosphatase, 5′-nucleotidase, and acid phosphatase were closely associated with IMP, Hx, and HxR conversion, respectively. Aeromonas, Serratia, Lactococcus, Pseudomonas, and Peptostreptococcus notably influenced flavor metabolism and enzyme activities. The metabolism disparities of valine, leucine, isoleucine, lysine, and α-linolenic acid could be the primary factors contributing to flavor metabolism distinctions. This study offers novel insights into the flavor change mechanisms and potential regulation strategies of bighead carp during storage.

Comprehensive analysis of the metabolome and the whole genome transcriptome to reveal the regulatory mechanism the flavor of Phallus rubrovolvatus

Phallus rubrovolvatus (P. rubrovolvatus) is a large and rare fungus widely consumed and used for medicinal purposes in East Asian countries, earning the reputation of "plant meat". We created a reference genome for P. rubrovolvatus, with an assembly length of 33.39 Mb and 144 overlapping groups. We identified 9,204 coding genes on the genome, of which 231 gene clusters are related to amino acid synthesis and transport. In this study, via integrating the flavor-related metabolite and transcriptome data of five different developmental stages of P. rubrovolvatus, we produced a global map of the alterations in flavor-related metabolites throughout the entire development process of P. rubrovolvatus. With this dataset, we constructed a complex regulatory network, thereby identifying the key structural genes and metabolites for the regulation of free amino acids in the flavor formation of P. rubrovolvatus, and glutathione and 5′-nucleotides possess a strong synergistic fresh-enhancing effect. In the five different developmental stages of P. rubrovolvatus, the regulation of the identified genes related to the synthesis of amino acids and derivatives on flavor metabolism has been confirmed, which demonstrates that our dataset offers a suitable instrument for elucidating the regulatory substances that control the flavor biosynthetic pathways, which were previously not elucidated. Overall, our research findings not only provide novel insights into the metabolic regulation of flavor during the mycelia developmental process of P. rubrovolvatus, but also lay the groundwork for enhancing the flavor of P. rubrovolvatus.

Integrative metagenomics, volatilomics and chemometrics for deciphering the microbial structure and core metabolic network during Chinese rice wine (Huangjiu) fermentation in different regions

Huangjiu is a spontaneously fermented alcoholic beverage, that undergoes intricate microbial compositional changes. This study aimed to unravel the flavor and quality formation mechanisms based on the microbial metabolism of Huangjiu. Here, metagenome techniques, chemometrics analysis, and headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC–MS) metabolomics combined with microbial metabolic network were employed to investigate the distinctions and relationship between the microbial profiles and the quality characteristics, flavor metabolites, functional metabolic patterns of Huangjiu across three regions. Significant variations (P < 0.05) were observed in metabolic rate of physicochemical parameters and biogenic amine concentration among three regions. 8 aroma compounds (phenethyl acetate, phenylethyl alcohol, isobutyl alcohol, ethyl octanoate, ethyl acetate, ethyl hexanoate, isoamyl alcohol, and diethyl succinate) out of 448 volatile compounds were identified as the regional chemical markers. 25 dominant microbial genera were observed through metagenomic analysis, and 13 species were confirmed as microbial markers in three regions. A metabolic network analysis revealed that Saccharomycetales (Saccharomyces), Lactobacillales (Lactobacillus, Weissella, and Leuconostoc), and Eurotiales (Aspergillus) were the predominant populations responsible for substrate, flavor (mainly esters and phenylethyl alcohol) metabolism, Lactobacillales and Enterobacterales were closely linked with biogenic amine. These findings provide scientific evidence for regional microbial contributions to geographical characteristics of Huangjiu, and perspectives for optimizing microbial function to promote Huangjiu quality.

Microbial community variation and flavor metabolism in low-salt Chinese horse bean-chili-paste: Insights from bioturbation fermentation

Chinese horse bean-chili-paste (CHCP) is a traditional and famous high-salt fermented condiment in southwest China, and salt reduction strategy in this industry is imperative. In this study, we investigated the effect of inoculation with two endogenous strains (Tetragenococcus halophilus and Wickerhamiella versatilis) on the products quality at different salinity. The results showed that salt reduction combined with microbial inoculation showed prominent impact on the volatile profile. A total of 15 compounds was identified as key flavors, and bioturbation fermentation could significantly promote the concentrations of many pleasant aroma volatiles. Quantitative microbial profile analysis identified 29 key genera that might benefit microbial stability. In addition, bioturbation fermentation stimulated more microbial communities to contribute to the formation of key flavors. Moreover, the metabolic pathways of key flavor compounds were further investigated and preliminary results suggest that bioturbation under low-salt conditions promotes high expression of enzymes involved in the formation of these compounds, thereby increasing the abundance of key flavor compounds. These results revealed the variations of microbial communities in low-salt CHCP after biofortification fermentation and their influences on flavor metabolism, which could provide references for the manufacture of low-salt fermented foods.

Investigation into spatial profile of microbial community dynamics and flavor metabolites during the bioaugmented solid-state fermentation of Baijiu

Biofortification of Baijiu fermentation using exogenous functional strains can change the microbial community structure of the fermentation ecosystem and flavor metabolism, which can impact Baijiu flavor. In this work, a high ethyl hexanoate-producing Saccharomyces cerevisiae Y285 strain was added for biofortification to investigate microbial communities' succession and flavor compounds throughout the fermentation of strong-flavor Baijiu. The microbial community composition of the fermentation samples was analyzed using the Illumina MiSeq platform, and the results showed that Pediococcus, Lactobacillus, Weissella and Saccharomyces were the dominant genera. A total of 111 flavor compounds, consisting of esters (50), alcohols (14), acids (3), aldehydes (9), phenols (9), pyrazines (3), ketones (8), and others (15), were detected in all samples, and the content of total esters of the fortified Daqu increased dramatically. Among them, the content of ethyl acetate decreased while that of ethyl hexanoate increased significantly, and the content of other compounds such as ethyl palmitate, ethanol, phenethyl alcohol and tetramethylpyrazine also increased. Redundancy analysis and Spearman's correlation analysis revealed that Saccharomyces, Pediococcus, Lactobacillus, and Weissella were significantly positively correlated with esters and alcohols. To summarize, biofortification with S. cerevisiae during Baijiu fermentation modifies microbial community composition, as well as the content of ethyl hexanoate in Baijiu, and induces changes in the content of other flavor compounds. These findings imply that modifying the microorganisms throughout the Baijiu fermentation process can alter the flavor of Baijiu and further enhance it.

Moringa oleifera leaf improves meat quality by modulating intestinal microbes in white feather broilers

Moringa oleifera addition to animal diets can improve the growth performance, intestinal health, and immunity of animals, without adverse effects. We investigated the effects of Moringa oleifera on the growth performance, meat quality, and intestinal health of broilers. Moringa oleifera and fermented Moringa oleifera could improve the flesh color and breast muscle tenderness of broilers (p < 0.05). The contents of essential amino acids, unsaturated fatty acids, ΣMUFA, P/S and n-3 ratio in breast muscle of broilers were dose-increased, and the effect of fermented Moringa oleifera was better. Moringa oleifera and fermented Moringa oleifera regulated chicken flavor metabolism by increasing the relative abundance and Short-chain fatty acid (SCFA) contents of Bacteroides, Spirillum, and lactic acid bacteria. Overall, supplementation with 1 % fermented Moringa oleifera can significantly increase essential amino acid and unsaturated fatty acid contents in broilers and participate in the synthesis and transformation of amino acids and fatty acids regulated by beneficial bacteria.

Improving the aroma profile of inoculated fermented sausages by constructing a synthetic core microbial community.

Commercial starter cultures play a critical role in the industrial production of fermented sausages. However, commercial starter cultures could not reproduce the metabolic actions of diverse microorganisms and the aroma profile of the traditional spontaneously fermented sausages. Identifying the core microbial community in spontaneously fermented sausages will facilitate the construction of a synthetic microbial community for reproducing metabolic actions and flavor compounds in spontaneously fermented sausages. This study aimed to reveal the core microbial community of spontaneously fermented sausages based on their relative abundance, flavor-producing ability, and co-occurrence performance. We identified five promising genera to construct the synthetic core microbial community, these were Lactobacillus, Staphylococcus, Macrococcus, Streptococcus, and Pediococcus. Sausages inoculated with a synthetic core microbial community presented higher quality of aroma profile than the fermented sausages inoculated with a commercial starter culture. Some important volatile flavor compounds of spontaneously fermented sausage, such as (-)-β-pinene, β-caryophyllene, 3-methyl-1-butanol, α-terpineol, ethyl 2-methylpropanoate, and ethyl 3-methylbutanoate which are associated with floral, fruity, sweet, and fresh aromas, were also detected in fermented sausage inoculated with synthetic microbial community. This indicated that the synthetic core microbial community efficiently reproduced flavor metabolism. Overall, this study provides a practical strategy to design a synthetic microbial community applicable to different scientific fields.

Environmental factors induced metabolome shifts during Laobaigan-flavor Baijiu fermentation

Environmental factors are the key factors affecting the fermentation of traditional fermented foods. However, the effects of environmental factors on flavor metabolism of Laobaigan-flavor Baijiu have not been described. In this study, we applied HS-SPME–GC–MS and physicochemical parameters analysis to reveal the dynamic of volatile flavor compounds and environmental factors, and indicated the effects of environmental factors on the succession of volatile flavor compounds. The fermentation process was divided into three stages: alcohols (628 mg/kg) and acids reached higher in the early stage (0–8 days), while aldehydes existed more in the middle stage (10–17 days) and esters accumulated until the middle (2501 mg/kg) or later (1168 mg/kg) stages (20–29 days). Meanwhile, environmental factors changed rapidly (p < 0.05), and significantly correlated with the formation of flavor compounds at different stages. Among them, pH and protein content were significantly related to esters (|r| > 0.6) esterified by monocarboxylic acid in the middle stage, while esters (|r| > 0.7) synthesized with hydroxyl acid had significant relations with temperature and moisture in the later stage. Our study indicated the correlations between the dynamic of environmental factors and the succession of volatile flavor compounds, and it provided a potential approach to manage environmental factors to improve the fermentation of Baijiu.

Metagenomic analyses reveal microbial communities and functional differences between Daqu from seven provinces

Microbial communities perform the brewing function in Daqu. Macrogenomics and PICRUST II analyses revealed the differences in microbes and metabolic functions among Daqu from the seven Baijiu-producing provinces. Jiang-flavored Daqu (Guizhou, Shandong, and Hubei provinces) generally forms an aroma-producing functional microbiota with Kroppenstedtia, Bacillus, Thermoascus, Virgibacillus, and Thermomyces as the core, which promotes the metabolism of various amino acids and aroma compounds. Light-flavored Daqu (Shanxi Province) enriched the Saccharomycopsis, Saccharomyces, and lactic acid bacteria (LAB) microbiota through low-temperature fermentation. These microbes can synthesize alcohol and lactic acid but inhibit amino acid metabolism within the Light-flavored Daqu. Bifidobacterium and Saccharomycopsis were dominant in the Tao-flavored Daqu (Henan province). This unique microbial structure is beneficial for pyruvate fermentation to lactate. Research also found that Strong-flavored Daqu from Jiangsu and Sichuan provinces differed significantly. The microbial communities and metabolic pathways within Jiangsu Daqu were similar to those within Jiang-flavored Daqu, but Sichuan Daqu was dominated by Thermoascus, LAB, and Thermoactinomyces. In addition, Spearman correlation analysis indicated that Kroppenstedtia, Bacillus, and Thermomyces were not only positively related to flavor metabolism but also negatively correlated with Saccharomycopsis. This research will help establish a systematic understanding of the microbial community and functional characteristics in Daqu.

Ozone micro-nano bubble water preserves the quality of postharvest parsley

The production and use of ozone micro-nano bubble water (O3-MNBW) is an innovative technology that prolongs the reactivity of aqueous-phase ozone and maintains the freshness and quality of fruits and vegetables by removing pesticides, mycotoxins, and other contaminants. The quality of parsley treated with different concentrations of O3-MNBW was investigated during storage at 20 ℃ for 5 d, and found that a ten-minute exposure of parsley to 2.5 mg·L−1 O3-MNBW effectively preserved the sensory quality of parsley, and resulted in lower weight loss, respiration rate, ethylene production, MDA levels, and a higher level of firmness, vitamin C, and chlorophyll content, relative to untreated parsley. The O3-MNBW treatment also increased the level of total phenolics and flavonoids, enhanced peroxidase and ascorbate peroxidase activity, and inhibited polyphenol oxidase activity in stored parsley. Five volatile signatures identified using an electronic nose (W1W, sulfur-compounds; W2S, ethanol; W2W, aromatic- and organic- sulfur compounds; W5S, oxynitride; W1S, methane) exhibited a significant decrease in response to the O3-MNBW treatment. A total of 24 major volatiles were identified. A metabolomic analysis identified 365 differentially abundant metabolites (DMs). Among them, 30 and 19 DMs were associated with characteristic volatile flavor substance metabolism in O3-MNBW and control groups, respectively. The O3-MNBW treatment increased the abundance of most DMs related to flavor metabolism and reduced the level of naringin and apigenin. Our results provide insight into the mechanisms that are regulated in response to the exposure of parsley to O3-MNBW, and confirmed the potential use of O3-MNBW as a preservation technology.

Correlation between microbial diversity and flavor metabolism in Huangshui: A by-product of solid-state fermentation Baijiu

Huangshui (HS), a by-product of solid-state fermentation Baijiu, is being given more attention on comprehensive utilization because of its abundant microbial and nutritional resources. To effectively utilize HS for improving the economic benefits, correlations between microbial community and flavor compounds in different HS samples were uncovered in the present study. Lactobacillus, Methanobacterium, Methanobrevibacter, Methanoculleus, and Methanosarcina were dominant genera in all the samples. Additionally, Caproiciproducens and Clostridium were positively related with Methanosaeta, while Lactobacillus exhibited a negative relationship with occurrence of Methanobacterium, Methanoplasma, and Methanolobus. Linear discriminant analysis effect size (LEfSe) showed that 33 flavor compounds mainly including caproic acid, butyric acid, acetic acid, and ethyl caproate, were significantly different between the samples, and these compounds were positively correlated with Ruminococcaceae, Bacteroides, and methanogenic archaea by redundancy analysis (RDA). Furthermore, abundant genes encoding enzymes participated in glycolysis pathway and carboxylic acid chain elongation process which involved in formation of caproic acid and butyric acid were observed by Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt2). These results provided scientific basis of microbiota and their flavor metabolism in HS, and laid theoretical foundation for rational and effective utilization of microbial functions in HS.

Amino Acids Drive the Deterministic Assembly Process of Fungal Community and Affect the Flavor Metabolites in Baijiu Fermentation.

Nutrient fluctuation is ubiquitous in fermentation ecosystems. However, the microbial community assembly mechanism and metabolic characteristics in response to nutrient variation are still unclear. Here, we used Baijiu fermentation as a case example to study the responses of microbial community assembly and metabolic characteristics to the variation of amino acids using high-throughput sequencing and metatranscriptomics analyses. We chose two fermentation groups (group A with low amino acid and group B with high amino acid contents). The two groups showed similar succession patterns in the bacterial community, whereas they showed different succession in the fungal community wherein Pichia was dominant in group A and Zygosaccharomyces was dominant in group B. The β-nearest taxon index (βNTI) revealed that bacterial community was randomly formed, whereas fungal community assembly was a deterministic process. Variance partitioning analysis and redundancy analysis revealed that amino acids showed the largest contribution to the fungal community (37.64%, P = 0.005) and were more tightly associated with it in group B. Further study revealed that serine was positively related to Zygosaccharomyces and promoted its growth and ethanol production. Metatranscriptomic analysis revealed that the differential metabolic pathways between the two groups mainly included carbohydrate metabolism and amino acid metabolism, which explained the differences of ethanol production and volatile metabolites (such as isoamylol, isobutanol, and 2-methyl-1-butanol). Then these metabolic pathways were constructed and related gene expression and active microorganisms were listed. Our study provides a systematical understanding of the roles of amino acids in both ecological maintenance and flavor metabolism in fermentation ecosystems. IMPORTANCE In spontaneous fermented foods production, nutrient fluctuation is a critical factor affecting microbial community assembly and metabolic function. Revealing the microbial community assembly mechanism and how it regulates its metabolic characteristics in response to nutrient variation is helpful to the management of the fermentation process. This study provides a systematical understanding of the effect of amino acids on the microbial community assembly and flavor metabolisms using Baijiu fermentation as a case example. The data of this study highlight the importance of the nutrient management in fermentation ecosystems.

Metabolomic analyses provides insight into the fruit nutritional and sensory attributes among 'Guanxi' pummelo and its bud mutants

The biochemical compositions in pummelo (<italic>Citrus maxima</italic>) fruits are key determining factors for the formation of nutrients and flavor. In this study, sensory (soluble solids, acidity and volatiles) and nutritional (vitamin C, carotenoids, phenols, flavonoids and antioxidant activity) profiles of fruit samples from 'Guanxi' pummelo and its four bud mutants were investigated. 'Guanxi' and 'Hongzuan', two pale-fleshed pummelo cultivars, contained relatively lower levels of carotenoids, vitamin C, phenols and total antioxidant activity compared to the other pummelos with red or yellow flesh. A total of 92 and 167 volatile compounds were detected in the pulp and flavedo of pummelo fruits, respectively. The majority of the different pulp volatiles were ketones, terpenes, alcohols and aldehydes, and were highly accumulated in 'Guanxihuang' pummelo (yellow-fleshed). The contents of volatiles in flavedo (285.85−955.88) were much larger than those in pulp (6.05−26.85) samples. Limonene was the most abundant volatile in flavedo, ranging from 133.28 in 'Hongzuan' to 480.36 in 'Guanxi'. The candidate genes <italic>TPS1</italic> and <italic>LOX2.1</italic> were associated with the amounts of terpenes and aldehydes in pummelo fruits. 'Sanhong' and 'Guanxihuang' fruits were preferred by tasters for their strong aroma, rich sweet and moderately sour taste, and high nutritional constituents. These results may provide insight into understanding the flavor metabolism pathways in pummelo fruits and facilitate further genetic improvement of pummelo fruit quality.

Effects of solid-state fermentation with Bacillus subtilis Y4 on the quality of Yibin Yacai

Bacillus spp. has been proven to be critical for the quality of many fermented foods, but as one of the domain bacteria, its effect on the quality of Yibin Yacai has not been fully addressed. Herein, the effects of inoculation of Bacillus subtilis Y4 on the physicochemical properties, flavor metabolism and microbial community changes of Yibin Yacai for three-month solid-state fermentation were investigated. The results showed that inoculation of B. subtilis Y4 could reduce the pH and salinity of Yibin Yacai, accelerate the consumption of nitrite, promote the growth of Lactobacillus and the production of sweet amino acid, and inhibit pathogenic microorganisms at the late fermentation stage. During solid-state fermentation, the dominant fungus Cystofilobasidium was positively correlated with most volatile flavor substances, which were indirectly affected by B. subtilis Y4. Furthermore, compared to spontaneous fermented Yibin Yacai, inoculation of B. subtilis Y4 promoted the production of alkenes and made the peak of ester content appear earlier. These results indicated that inoculation of B. subtilis Y4 for solid-state fermentation could improve the quality and taste of Yibin Yacai, and shorten the fermentation time.

Effect of coating on flavor metabolism of fish under different storage temperatures.

Two edible coatings (gelatin coating and ginger essential oil-gelatin coating) were prepared to maintain the flavor quality of fish fillets at two storage temperatures (4°C and 25°C). The effects of coating on fish fillets were evaluated by detecting the physical properties, microstructure, microbial properties, volatile flavor and taste flavor of fish. In the same coating method, fish fillets stored at 4°C showed better effect than that at 25°C on maintain water content, color and texture, however, fish fillets stored at 25°C were closer to fresh fish in volatile flavor and taste flavor than that at 4°C; whatever the storage temperature, coating could slow down the growth of fish microorganisms, maintain water content, color, texture, volatile flavor and taste flavor of fish fillets; GGC exhibited better effect on maintain flavor quality than GC.

The regulation of nutrient and flavor metabolism in tomato fruit

The accumulation of nutrients and flavors are important factors that determine the consumption of tomato fruit. Carotenoids, polyphenol and vitamin C belong to antioxidant molecules and have been proven to regulate several biochemical processes and prevent many chronic diseases. In recent years, significant progress has been made in our understanding of the biosynthetic pathway and regulatory networks of these compounds in tomatoes. Numerous genes have been determined which promote the accumulation of these nutrients, such as <italic>SlNAC1</italic>, <italic>SlCCD</italic>, <italic>SlHY5</italic>. Meanwhile, since the mechanisms that control nutrient metabolism during fruit ripening are systematic and sophisticated, there are still many unknown factors that affect their content, which need to be further explored. In addition, not only are nutritional properties important, but flavor profiles play a core role in the market for tomato production. However, it is generally accepted by consumers that many tomato varieties have declined nutrient content and little flavor with people's pursuit of fruit yield and size. Hence, improving their levels are the main objectives of many breeding programs. In order to effectively enhance the nutritional and flavor quality of tomato fruits, we reviewed the critical steps in metabolic pathways of these important nutrients and flavor compounds, summarized key regulators for controlling the accumulation of these compounds, and hope to offer valuable candidate genes for the production of high-quality tomato fruits.

Characterizing the correlation between species/strain-specific starter with community assembly and metabolic regulation in Xiaoqu Pei

Studying the correlation between microbiome metabolism and flavor of fermented foods has garnered significant attention recently. Understanding the contribution of metabolic regulation and environmental stress to microecosystems is essential for exploring the mechanisms of action of traditional fermented foods. Here, the interaction between microbial communities was investigated using a Xiaoqu fermentation system, processed as "simulative microecosystems," in which starters were composed of Rhizopus-specific species/strains, Meyerozyma guilliermondii, and Bacillus licheniformis. The differences between community succession and metabolites were also explored. The results indicated that Rhizopus species/strain specificity affected starch hydrolyzation, resulting in a remarkable difference in the type and content of organic acids. This further suggested that the differences in nutrient abundance and organic acids influenced the colonization of microorganisms in the fermentation system, thereby influencing the succession of their communities. The fungi in the community predominantly originated from starters, whereas the bacteria were derived from both the environment and starter. Environmentally colonized microbes were the major contributors to the co-occurrence network and were strongly correlated with network. Regional characteristics of fermented foods were closely related to environmental microbes. These results contribute to the understanding of microbial assembly and flavor metabolism in fermented foods and provide strategies for quality regulation.

Integrative analyses of metabolome and genome-wide transcriptome reveal the regulatory network governing flavor formation in kiwifruit (Actinidia chinensis).

Soluble sugars, organic acids and volatiles are important components that determine unique fruit flavor and consumer preferences. However, the metabolic dynamics and underlying regulatory networks that modulate overall flavor formation during fruit development and ripening remain largely unknown for most fruit species. In this study, by integrating flavor-associated metabolism and transcriptome data from 12 fruit developmental and ripening stages of Actinidia chinensis cv Hongyang, we generated a global map of changes in the flavor-related metabolites throughout development and ripening of kiwifruit. Using this dataset, we constructed complex regulatory networks allowing to identify key structural genes and transcription factors that regulate the metabolism of soluble sugars, organic acids and important volatiles in kiwifruit. Moreover, our study revealed the regulatory mechanism involving key transcription factors regulating flavor metabolism. The modulation of flavor metabolism by the identified key transcription factors was confirmed in different kiwifruit species providing the proof of concept that our dataset provides a suitable tool for clarification of the regulatory factors controlling flavor biosynthetic pathways that have not been previously illuminated. Overall, in addition to providing new insight into the metabolic regulation of flavor during fruit development and ripening, the outcome of our study establishes a foundation for flavor improvement in kiwifruit.

Research Progress on Relationship and Mechanism between Microbial Diversity and Flavor Development in Traditional Fermented Foods

Succession of microbial community structure in traditional fermented foods is complicated, and the metabolism pathways of flavor compounds are various during fermentation. As the “soul” of fermented foods, microorganisms influence the sensory, nutrition and functional characteristics of the fermented foods through a variety of metabolism pathways, which are closely related to the formation of flavor. Revealing the relationship between microorganism and flavor compounds is advantageous to identify the potential flavor-forming microorganism and regulate flavor characteristics of fermented foods. In this paper, the relationship between microorganism diversity and flavor development in the typical traditional fermented foods, including liquor, fermented vinegar, fermented vegetables and fermented animal products is mainly reviewed, and the flavor metabolism mechanisms of core microorganisms are briefly discussed. This review will provide some references for the quality improvement of traditional fermented foods.

Effect of enzymes addition on the fermentation of Chinese rice wine using defined fungal starter

A higher fermentation capability and quality of a rice wine was achieved, using mixed fungal (Rhizopus chinonsis R01, Asperigillus niger A20, Mucor pusillus M05 and Saccharomyces cerevisiae S10) starter fermentation of japonica rice supplemented with α-amylase (AM), glucoamylase (GAM) and acid protease (AP). Results showed that alcohol content, free amino acids (FAA) and volatile flavor substances concentrations were increased by 49.22%, 85.54%, and 25.71% compared with the control group respectively. To understand the role of enzymes during rice wine brewing, the effects of hydrolases on chemical and physical properties of cooking rice, on the yeast growth, enzyme productivity of molds were determined. Rice starch was hydrolyzed effectively by AM and GAM, the viscosity reduced significantly, the enzyme contact area expanded, which accelerated the further hydrolysis of japonica rice. Increase of hydrolysate promoted the fungi growth, while improved the ability of molds to produce enzymes. AP promoted the protease activity of M. pusillus M05 and A. niger A20, improved protein utilization, increased the content of FAA and formed higher level of flavor substances in rice wine. The results indicate that hydrolase addition can change the physic-chemical state of the mash to enhance microbial biotransformation and modify flavor metabolism.