Isolation and identification of bitter-tasting peptides in Shaoxing rice wine using ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry combined with taste orientation strategy

Impact of Glutinous Rice Varieties from Different Regions on Microbial Community Structure, Metabolic Profiles, and Flavor Characteristics of Chinese Rice Wine (Huangjiu)

Huangjiu is a traditional alcoholic beverage in China, but because of the differences in fermentation conditions and raw materials, how to optimize the flavor quality of Huangjiu is facing challenges. This study used high-throughput sequencing (HTS) to investigate microbial diversity in Huangjiu brewed from glutinous rice from five regions in China. Metabolic pathway annotation, electronic senses, and metabolite analysis elucidated the relationships between rice variety, microbial communities, flavor profiles, and metabolic characteristics of Huangjiu. Statistically significant differences in microbial community structure and flavor profiles were observed across Huangjiu samples (p < 0.05), with ten dominant microbial genera identified. Lactic acid bacteria (LAB) enriched in Guizhou and Hubei were positively correlated with higher organic acid (12.36 and 12.30 mg/mL, respectively) and lower amino acid levels (2985 and 2920 mg/L, respectively), contributing to a more pronounced sourness in these Huangjiu. Conversely, Huangjiu from Zhejiang, Guangxi, and Jilin exhibited higher concentrations of Saccharopolyspora, Saccharomonospora, Saccharomyces, and Bacillus, associated with elevated amino acid (3706, 3695, and 3700 mg/L, respectively) and reduced organic acid levels (10.11, 9.92 and 10.10 mg/mL, respectively), resulting in sweetness and bitterness. These findings provide valuable insights for optimizing Huangjiu flavor and quality through targeted microbial and fermentation management.

Novel insights into delayed bitterness control in traditional Huangjiu: Regulating bacterial community by inoculated with Saccharomyces cerevisiae SC-6

Under semi-open brewing conditions, traditional Huangjiu often suffers from unstable flavor quality, including occasional delayed bitterness. To address this issue, a yeast strain, Saccharomyces cerevisiae SC-6, was screened for its ability to reduce delayed bitterness. The effects of SC-6 on the flavor and microbial composition of Huangjiu exhibiting high levels of delayed bitterness were also investigated. GC-MS analysis indicated that S. cerevisiae SC-6 significantly lowered the levels of key delayed bitter compounds, including octanoic acid, ethyl caprylate, benzaldehyde, and phenol, by 54.80 %, 12.21 %, 31.38 %, and 43.23 %, respectively. PCoA analysis demonstrated that SC-6 altered the microbial community of traditional Huangjiu. Correlation analysis indicated that reduced bitter compounds correlated with changed abundances of Rhodopseudomonas, unclassified_f_Micromonosporaceae, Lachnoclostridium, Lactobacillus, Streptomyces, Clostridium_sensu_stricto_1, Staphylococcus, Pseudomonas, unclassified_o__Enterobacterales, and Candida. These results provide effective guidance for controlling off-flavors in traditional Huangjiu and clarify the role of microorganisms in the production of bitter substances.

The dynamic of physicochemical properties, volatile compounds and microbial community during the fermentation of Chinese rice wine with diverse cereals

This study investigates the impact of liquid state fermentation on the key flavor compounds and microbial community structure in Chinese rice wine brewed from five different raw materials: buckwheat, sorghum, japonica rice, glutinous rice, and black rice. Using HS-SPME-GC-MS and HPLC, the volatile compounds were analyzed across various grain liquefaction methods, detecting 82 volatiles, including esters, alcohols, aldehydes, and acids. The concentration of flavor compounds such as esters, amino acids, phenolic acids, and organic acids varied significantly depending on the raw material used. Based on odor activity values, 31 key compounds were identified, including 15 ethyl esters, like ethyl laurate, responsible for the unique and complex aroma of the rice wines. Bitter amino acids, making up over 50 % of the total amino acids, were predominant. Among the varieties, the buckwheat-fermented wine exhibited the highest ester content (27.39 mg/L), nearly double that of other samples, along with elevated amino acids (1.47 mg/mL) and phenolic acids (904.29 mg/L). Black rice ranked second in amino acid content (0.93 mg/mL), while glutinous rice had the highest organic acid content (239.76 mg/mL). Metagenomic sequencing on the fifth day of fermentation revealed significant differences in microbial community structure among the raw materials. Saccharomyces, Aspergillus, Thermomyces, Epicoccus, and Albertella were dominant fungi, while Weissella, Thermoactinomyces, Bacillus, and Saccharopolyspora were dominant bacteria. Sensory analysis showed that buckwheat-fermented rice wine was distinguished by its honey, floral, creamy, and umami attributes, while balancing alcohol, acidity, bitterness, and Qu aroma. The results demonstrate the significant influence of raw material selection and liquefaction method on both flavor profile and microbial diversity in Chinese rice wine.

Key umami taste contributors in Longjing green tea uncovered by integrated means of sensory quantitative descriptive analysis, metabolomics, quantification analysis and taste addition experiments

Umami taste is a key criteria of green tea quality evaluation. The aim of this study was to comprehensively explore the key umami taste contributors in Longjing tea. The taste and molecular profiles of 36 Longjing green tea infusions were characterized by sensory quantitative descriptive analysis and LC-MS based metabolomics, respectively. By uni-/multi-variate statistical analysis, 84 differential compounds were screened among tea infusions with varied umami perceptions. Among them, 17 substances were identified as candidate umami-enhancing compounds, which showed significant positive correlations with umami intensities. Their natural concentrations were accurately quantified, and their umami taste-modifying effects were further investigated by taste addition into glutamic acid solution. Glutamic acid, aspartic acid, glutamine, theanine, phenylalanine, histidine, theogallin, galloylglucose, 1,2,6-trigalloylglucose significantly enhanced the umami taste. This study uncovered for the first time of some bitter amino acids and galloylglucose homologous series as important umami-enhancers, which provided a novel perspective into the tea taste.

Odor and taste characteristics, transduction mechanism, and perceptual interaction in fermented foods: a review

Fermentation is a critical technological process for flavor development in fermented foods. The combination of odor and taste, known as flavor, is crucial in enhancing people's perception and psychology toward fermented foods, thereby increasing their acceptance among consumers. This review summarized the determination and key flavor compound screening methods in fermented foods and analyzed the flavor perception, perceptual interactions, and evaluation methods. The flavor compounds in fermented foods could be separated, purified, and identified by instrument techniques, and a molecular sensory science approach could identify the key flavor compounds. How flavor compounds bind to their respective receptors determines flavor perception, which is influenced by their perceptual interactions, including odor-odor, taste-taste, and odor-taste. Evaluation methods of flavor perception mainly include human sensory evaluation, electronic sensors and biosensors, and neuroimaging techniques. Among them, the biosensor-based evaluation methods could facilitate the investigation of the flavor transduction mechanism and the neuroimaging technique could explain the brain's signals that relate to the perception of flavor and how they compare to signals from other senses. This review aims to elucidate the flavor profile of fermented foods and highlight the significance of comprehending the interactions between various flavor compounds, thus improving the healthiness and sensory attributes.

Bitter flavors and bitter compounds in foods: identification, perception, and reduction techniques

Bitterness is one of the five basic tastes generally considered undesirable. The widespread presence of bitter compounds can negatively affect the palatability of foods. The classification and sensory evaluation of bitter compounds have been the focus in recent research. However, the rigorous identification of bitter tastes and further studies to effectively mask or remove them have not been thoroughly evaluated. The present paper focuses on identification of bitter compounds in foods, structural-based activation of bitter receptors, and strategies to reduce bitter compounds in foods. It also discusses the roles of metabolomics and virtual screening analysis in bitter taste. The identification of bitter compounds has seen greater success through metabolomics with multivariate statistical analysis compared to conventional chromatography, HPLC, LC-MS, and NMR techniques. However, to avoid false positives, sensory recognition should be combined. Bitter perception involves the structural activation of bitter taste receptors (TAS2Rs). Only 25 human TAS2Rs have been identified as responsible for recognizing numerous bitter compounds, showcasing their high structural diversity to bitter agonists. Thus, reducing bitterness can be achieved through several methods. Traditionally, the removal or degradation of bitter substances has been used for debittering, while the masking of bitterness presents a new effective approach to improving food flavor. Future research in food bitterness should focus on identifying unknown bitter compounds in food, elucidating the mechanisms of activation of different receptors, and developing debittering techniques based on the entire food matrix.

Exploring UPLC-QTOF-MS-based targeted and untargeted approaches for understanding wine mouthfeel: A sensometabolomic approach

This study aimed to establish relationships between wine composition and in-mouth sensory properties using a sensometabolomic approach. Forty-two red wines were sensorially assessed and chemically characterised using UPLC-QTOF-MS for targeted and untargeted analyses. Suitable partial least squares regression models were obtained for "dry", "sour", "oily", "prickly", and "unctuous". "Dry" was positively contributed by flavan-3-ols, anthocyanin derivatives (AntD), valine, gallic acid and its ethyl ester, and peptides, and negatively by sulfonated flavan-3-ols, anthocyanin-ethyl-flavan-3-ols, tartaric acid, flavonols (FOL), hydroxycinnamic acids (HA), protocatechuic ethyl ester, and proline. The "sour" model included molecules involved in "dry" and "bitter", ostensibly as a result of cognitive interactions. Derivatives of FOLs, epicatechin gallate, and N-acetyl-glucosamine phosphate contributed positively to "oily", as did vanillic acid, HAs, pyranoanthocyanins, and malvidin-flavan-3-ol derivatives for "prickly", and sugars, glutathione disulfide, AntD, FOL, and one HA for "unctuous". The presented approach offers an interesting tool for deciphering the sensory-active compounds involved in mouthfeel perception.

Recent advancements in the taste transduction mechanism, identification, and characterization of taste components

In the realm of human nutrition, the phenomenon known as taste refers to a distinctive sensation elicited by the consumption of food and various compounds within the oral cavity and on the tongue. Moreover, taste affects the overall comfort in the oral cavity, and is a fundamental attribute for the assessment of food items. Accordingly, clarifying the material basis of taste would be conducive to deepening the cognition of taste, investigating the mechanism of taste presentation, and accurately covering up unpleasant taste. In this paper, the basic biology and physiology of transduction of bitter, umami, sweet, sour, salty, astringent, as well as spicy tastes are reviewed. Furthermore, the detection process of taste components is summarized. Particularly, the applications, advantages, and distinctions of various isolation, identification, and evaluation methods are discussed in depth. In conclusion, the future of taste component detection is discussed.

Research Progress on Flavor and Quality of Chinese Rice Wine in the Brewing Process

Chinese rice wine (CRW) is a traditional and unique alcoholic beverage in China, favored by many consumers for its rich aroma, unique taste, and complex ingredients. Its flavor is primarily composed of volatile and nonvolatile compounds. These flavor compounds are partly derived from grains and starters (Qu), while the other part is produced by microbial metabolism and chemical reactions during the brewing process. Additionally, ethyl carbamate (EC) in CRW, a hazardous chemical, necessitates controlling its concentration during brewing. In recent years, numerous new brewing techniques for CRW have emerged. Therefore, this paper aims to collect aroma descriptions and thresholds of flavor compounds in CRW, summarize the relationship between the brewing process of CRW and flavor formation, outline methods for reducing the concentration of EC in the brewing process of CRW, and summarize the four stages (pretreatment of grains, fermentation, sterilization, and aging process) of new techniques. Furthermore, we will compare the advantages and disadvantages of different approaches, with the expectation of providing a valuable reference for improving the quality of CRW.

Preparation of Saltiness-Enhancing Enzymatic Hydrolyzed Pea Protein and Identification of the Functional Small Peptides of Salt Reduction

According to the correlation of saltiness determined by electronic tongue and perceived NaCl concentration, favorable enzymatic hydrolysis parameters were achieved to prepare the saltiness enhancing mixture peptides from pea protein. Six peptide fractions (F1, F2, F3, F4, F5, and F6) were isolated using Sephadex G-10 gel filtration. Among them, fraction F4 (0.1%) exhibited the highest saltiness (5.90 ± 0.03). The amino acid sequences of five main peptides identified by time-of-flight mass spectrometry were Tyr-Trp (367.40 Da), Gly-Glu-His-Glu (470.43 Da), Glu-Arg-Phe-Gly-Pro (604.65 Da), Gly-Ala-Gly-Lys (331.37 Da), and Pro-Gly-Ala-Gly-Asn (414.41 Da). Tyr-Trp (0.01%) in 0.4% NaCl solution had a 20% saltiness-enhancement compared with 0.4% NaCl solution. More salivary aldosterone was secreted after tasting hydrolysate or Tyr-Trp solutions via enzyme-linked immunosorbent assay, reflecting the improvement of human sensitivity to saltiness. Thereby, the saltiness-enhancing effect was confirmed for the small peptides from hydrolyzed pea protein and the main contributor was further identified.