Interaction between major catechins and umami amino acids in green tea based on electronic tongue technology.

Umami amino acids inhibit the bitter and astringent taste presentation of catechins, which is essential for the taste regulation of green tea. In this study, the concentration-intensity trends and taste threshold properties of major catechin monomers were investigated using an electronic tongue. The taste and chemical structure interactions between the ester-type catechins and theanine, glutamic acid (Glu), and aspartic acid (Asp) were further analyzed by in vitro simulation and analysis of their reciprocal chemical structures. The results showed that the bitterness and astringency of the major catechin monomers increased with increasing concentration, and their bitterness thresholds and their electron tongue response values were higher than those of the astringent values, while the bitterness and astringency of the ester-type catechins were higher than those of the nonester type. The three amino acids inhibited the bitterness intensity of ester catechins (epigallocatechin gallate, epicatechin gallate, and gallocatechin gallate) at different concentrations, and the effects on the astringency intensity of ester catechins were complicated. Ester catechins significantly enhanced the umami intensity of theanine, Glu, and Asp at different concentrations. Their reciprocal chemical structures showed that hydrogen bonding was the main interaction force between the three ester-type catechins and the umami amino acids, with theanine and Glu interacting more strongly with ester-type catechins than Asp, and Glu having a lower binding energy to ester-type catechins, which bonded more easily.

Developing novel oenological tannins from 44 plants sources by assessing astringency and color in model wine.

BACKGROUND: Oenological tannins are commercial natural products extracted from different botanical sources, which were widely reported as prominent contributors to wine quality. Research on wine quality affected by tannins extracts promoted the development of new oenological products with low cost and high accessibility. In the present study, the structure and concentration of tannin in polyphenol extracts, as well as their correlation with astringency and the color of model wine, was investigated by UV spectrophotometer, HPLC, fluorescence quenching, sodium dodecylsulfate-polyacrylamide gel electrophoresis, colorimeter and sensory evaluation. RESULTS: Resource extracts from 16 of 44 plants were screened as wine oenological tannins, according to the total polyphenol and total flavanol, as well as the intensity of astringency and bitterness. Polyphenols extracted from grape seeds and green tea were more effective in increasing the wine astringency compared to other plant tannins. CONCLUSION: Total flavanol content and tannin activity showed a strong correlation with wine astringency. Condensed tannins with mean degree of polymerization also exhibited strong color stability, and the concentrations of (-)-epigallocatechin were associated with the a* value, a negative qualitative factor for wine color. The present study provides new clues regarding the development of low-cost and highly accessible sources of polyphenol extracts and lays a theoretical foundation for the development of the oenological product. © 2022 Society of Chemical Industry.

Exploring The Relative Astringency of Tea Catechins and Distinct Astringent Sensation of Catechins and Flavonol Glycosides via an In Vitro Assay Composed of Artificial Oil Bodies.

Artificial oil bodies covered by a recombinant surface protein, caleosin fused with histatin 3 (a major human salivary peptide), were employed to explore the relative astringency of eight tea catechins. The results showed that gallate-type catechins were more astringent than non-gallate-type catechins, with an astringency order of epicatechin gallate > epigallocatechin gallate > gallocatechin gallate > catechin gallate > epigallocatechin > epicatechin > gallocatechin > catechin. As expected, the extension of brewing time led to an increase in catechin content in the tea infusion, thus elevating tea astringency. Detailed analysis showed that the enhanced proportion of gallate-type catechins was significantly higher than that of non-gallate-type catechins, indicating that tea astringency was elevated exponentially, rather than proportionally, when brewing time was extended. Rough surfaces were observed on artificial oil bodies when they were complexed with epigallocatechin gallate (a catechin), while a smooth surface was observed on those complexed with rutin (a flavonol glycoside) under an atomic force microscope and a scanning electron microscope. The results indicate that catechins and flavonol glycosides induce the sensation of rough (puckering) and smooth (velvety) astringency in tea, respectively.

The effect of enzyme treatment on polyphenol and cell wall polysaccharide extraction from the grape berry and subsequent sensory attributes in Cabernet Sauvignon wines.

Pectolytic enzyme maceration is common for producing red wines, but the effects on bitterness and astringency are not well understood. Glycan microarrays assessed polysaccharide diversity and with polyphenol analysis was correlated with sensory data on descriptors of astringency and their perceived levels in enzyme-crafted Cabernet Sauvignon wines. Enzyme use is shown to have no effect on bitterness, but enzyme-macerated wines are more astringent. The data suggests that pectolytic enzymes are much more pronounced in their effect on the cell wall matrix than the ripeness of the berries at harvest and subsequent sensory perception. Enzyme-macerated red wines showed higher levels of polyphenol which were more polymerized and galloylated. The polyphenol-rich wines were described as hard, chalky, grippy, grainy and dry. The non-enzyme wines had elevated levels of arabinogalactan protein and pectin epitopes (notably biomarker mAbs JIM8 and JIM13) with the wines being characterized as soft, fine and velvety.

Widely targeted metabolomics analysis of white peony teas with different storage time and association with sensory attributes.

The sensory features of white peony teas (WPTs) significantly change with storage age; however, their comprehensive associations with composition are still unclear. This study aimed to clarify the sensory quality-related chemical changes in WPTs during storage. Liquid chromatography-tandem mass spectrometry based on widely targeted metabolomics analysis was performed on WPTs of 1-13 years storage ages. Weighted gene co-expression network analysis (WGCNA) was used to correlate metabolites with sensory traits including color difference values and taste attributes. 323 sensory trait-related metabolites were obtained from six key modules via WGCNA, verified by multiple factor analysis. The decline and transformation of abundant flavonoids, tannins and amino acids were related to the reduced astringency, umami and increased browning of tea infusions. In contrast, the total contents of phenolic acids and organic acids increased with storage. This study provides a high-throughput method for the association of chemical compounds with various sensory traits of foods.

Dynamic changes of metabolic profile and taste quality during the long-term aging of Qingzhuan Tea: The impact of storage age.

Qingzhuan tea (QZT) with longer aging year is usually believed to have higher quality and commercial value. In this study, a 20 years sequence of aged QZT were subjected to an electronic tongue and liquid chromatography-mass spectrometry to investigate the effect of storage age on its metabolic profile and taste quality. The changes in both taste quality and metabolic profile exhibited a parabolic trend in the 20 years of QZT aging and reached the maximum at the 10th year. A total of 47 compounds were identified as critical metabolites responsible for the age variation of QZT quality, with the methylation of catechins, glycosylation of flavonoids, degradation of flavoalkaloids, biosynthesis of triterpenoids, and formation of theabrownins. These results suggested that the taste of QZT was improved after 10 years of storage, with the reduction of bitterness and astringency and a general increase of key quality-related compounds.

Targeted and nontargeted metabolomics analysis for determining the effect of storage time on the metabolites and taste quality of keemun black tea.

The black tea could be stored for a long time, and subsequently affects the flavor characteristics. In the present study, the effects of storage years (1, 2, 3, 4, 5, 10, 17 and 20 years) on the chemical profiling and taste quality of keemun black tea (KBT) were compared by metabolomics and quantitative sensory evaluation. The main polyphenols were degraded during the storing, especially 10-year storage, but caffeine and theobromine were stable. The intensity of bitterness, astringency, umami was negatively correlated to storage years, with correlation coefficient at -0.95, -0.91 and -0.83 respectively, whereas sweetness had positive correlation coefficient at 0.74. Quinic acid, galloylated catechins, linolenic acid, linoleic acid, malic acid, palamitic acid, and theaflavin-3́-gallate were marker compounds which were responsible for distinguishing short and long time preserved KBT. The contents of fatty acids were positively correlated to storage time and sweet intensity.

Soluble cell wall carbohydrates and their relationship with sensory attributes in Cabernet Sauvignon wine.

The chemical and sensory profiles of wines prepared from Cabernet Sauvignon grapes at different ripening stages vary greatly. Here, the soluble cell wall carbohydrate (SCWC) and phenolic profiles of wines were analyzed in parallel with the sensory evaluation of their mouthfeel and taste characteristics. Both SCWCs and phenolic compounds correlated with wine mouthfeel. When analyses were extended to specific classes of cell wall carbohydrates, it was shown that rhamnogalacturonan I/II, arabinan, arabinogalactan types I and II and xyloglucan from grapes were the key determinants of overall mouthfeel descriptors, particularly viscosity, astringency and roughness, whereas heteromannan from grapes was associated with mouth coating and chalkiness. A perceived sour taste was notably associated with higher homogalacturonan contents. This finding provides insights into the contributions of non-phenolic compounds to wine mouthfeel. The data provide opportunities for the development of simple monosaccharide marker assays to monitor major mouthfeel characteristics in red wines.

Quantitative analyses of the bitterness and astringency of catechins from green tea.

Bitterness and astringency are two important quality attributes of green tea infusion, and catechins are the main contributor to the bitterness and astringency. The aim of this work was to quantitatively analyse the bitterness and astringency of green tea infusion according to the concentrations of catechins. The concentration-taste curves of catechins showed a pattern that fit the cubic functions, and their R2 values were higher than 0.956. The bitterness of green tea was highly correlated with the concentrations of (-)-epigallocatechin gallate and (-)-epicatechin gallate (ECG) (R2 = 0.7769, p < 0.01), and the astringency (R2 = 0.7878, p < 0.01) was highly correlated with the concentrations of ECG and flavonol glycosides (myricetin 3-O-galactoside and quercetin-3-O-rutinoside). Taste interactions between different catechins and between catechins and other substances were determined. These results may enhance the understanding of tea chemistry for improving the taste of products from green tea.

Application of metabolomics profiling in the analysis of metabolites and taste quality in different subtypes of white tea.

Three subtypes of white tea, Silver Needle (SN), White Peony (WP), and Shou Mei (SM), differ in their taste, aroma, bioactivity, and commercial value. Here, a metabolomics investigation on the chemical compositions combining taste equivalent-quantification and dose-over-threshold (DoT) determination on the taste qualities were applied to comprehensively characterize the white tea subtypes for the first time. Significant differences in the contents of catechins, dimeric catechins, amino acids, phenolic acids, flavonol/flavone glycosides, and aroma precursors were observed among these 3 white teas. Metabolite content comparison and partial least-squares (PLS) analysis suggest that theanine, aspartic acid, asparagine, and AMP were positively correlated with the umami taste in white tea, and flavan-3-ols, theasinensins, procyanidin B3, and theobromine had positive correlations with higher bitterness and astringency tastes. In addition, puckering astringent (-)-epigallocatechin gallate (EGCG), (-)-epicatechin gallate (ECG) and theogallin, bitter-tasting caffeine, and the mouth-drying/velvety-like astringent γ-aminobutyric acid (GABA) were identified as key taste compounds of white tea infusion by absolute quantification and DoT factor calculations. This work provided systematic and comprehensive knowledge on the chemical components, taste qualities, and sensory active metabolites for the subtypes of white tea.

Augmentation of chemical and organoleptic properties in Syzygium cumini wine by incorporation of grape seeds during vinification.

The role of grape seed tannins on improving organoleptic properties and its involvement in color stabilization in red wine are well established. The addition of grape seeds as the source of condensed tannins in fruit wine may provide a solution for its color instability and improvement of sensory attributes. Syzgium cumini is traditionally known for its therapeutic properties. In the current study, the influence of yeasts and grape seed addition during fermentation on the chromatic, phenolic and sensory attributes of the wine was accessed. Grape seed addition improved the color characteristics of wine and increased overall phenolic composition. Analysis by HPLC revealed 6 major anthocyanins, among which 3, 5-diglucoside form of delphidin and petunidin was found to be the major components. Cluster and PLSR analysis explained the impact of seed addition on the yeasts, as well as on the perception of panelists, with bitterness and astringency as the dominating attributes.

In vitro assay to estimate tea astringency via observing flotation of artificial oil bodies sheltered by caleosin fused with histatin 3.

Astringency, a sensory characteristic of food and beverages rich in polyphenols, mainly results from the formation of complexes between polyphenols and salivary proteins, causing a reduction of the lubricating properties of saliva. To develop an in vitro assay to estimate the astringency of oolong tea infusion, artificial oil bodies were constituted with sesame oil sheltered by a modified caleosin fused with histatin 3, one of the human salivary small peptides. Aggregation of artificial oil bodies was induced when they were mixed with oolong tea infusion or its major polyphenolic compound, (-)-epigallocatechin gallate (EGCG) of 100µM as observed in light microscopy. The aggregated artificial oil bodies gradually floated on top of the solution and formed a visible milky layer whose thickness was in proportion to the concentrations of tea infusion. This assay system was applied to test four different oolong tea infusions with sensory astringency corresponding to their EGCG contents. The result showed that relative astringency of the four tea infusions was correlated to the thickness of floated artificial oil bodies, and could be estimated according to the standard curve generated by simultaneously observing a serial dilution of the tea infusion with the highest astringency.

[Quantification of astringency for traditional Chinese medicine based on animal preference index and electronic tongue].

Current evaluation method for astringency is mainly focused on human sensory evaluation. However, it is subjective, vague, and short of assessment indicators for objective quantification. In this paper, the quantification method for astringent intensity of traditional Chinese medicine was established based on the animal preference index and electronic tongue in vitro and in vivo. Firstly, the standard substance of astringency, tannic acid, was used for the methodology optimization and validation of two-bottle preference test. It was determined that the standard experimental animals were female rats of 140-180 g. The functional relationship between concentration of tannic acid and preference index was obtained Y= ln(1.682 6－0.441 66X), r=0.997 3. Then the typical astringent Chinese herbs Chebulae Fructus, Ardisiae Japonicae Herba, Canarii Fructus, Catechu, and Arecae Pericarpium were evaluated by the optimized method. Their corresponding concentration of tannic acid was converted by the concentration-preference index relationship through preference index. Their astringency was equivalent to 0.56, 0.29, 0.24, 0.34, 0.25 g•L⁻¹ tannic acid. Finally, the results were verified by electronic tongue. The correction analysis between Euclidean distance in PCA and preference index and concentration of tannic acid converted by samples showed a high correlation through pearson correlation analysis. The above results indicated that the method was objective, true and reliable. The method provided a reliable tool for the quantification of astringency and evaluation of taste masking effect for Chinese medicines, and also offered a new idea and model for the quantification of taste in the pharmaceutical and food fields.

Influence of Grape Seeds and Stems on Wine Composition and Astringency.

The aim of this paper is to study the real influence of seeds and stems on wine composition, astringency, and bitterness. A decolored grape juice and a grape juice macerated for 4 days from the same Cabernet Sauvignon grapes were fermented with or without supplementation with 100% seeds, 300% seeds, or 100% stems. Once alcoholic fermentation had finished, the wines were analyzed and tasted. The presence of seeds and stems increased the concentration of flavan-3-ol monomers with respect to the controls. However, the seeds mainly released (+)-catechin and (-)-epicatechin, whereas the stems mainly released (+)-catechin and (+)-gallocatechin. The seeds and stems also released proanthocyanidins; those from seeds have a lower mDP and a high percentage of galloylation, whereas those from stems have a higher mDP and a relatively high percentage of prodelphinidins. The presence of seeds and stems brought about a slight but significant increase in pH and lowered titratable acidity and ethanol content. The presence of seeds boosted color intensity, whereas stems had the opposite effect. Finally, both seeds and stems increased wine astringency and bitterness.

Comparative analysis of three Callicarpa herbs using high performance liquid chromatography with diode array detector and electrospray ionization-trap mass spectrometry method.

Three Callicarpa species, namely Callicarpa nudiflora Hook. et Arn., Callicarpa macrophylla Vahl. and Callicarpa kwangtungensis Chun. are astringency and hemostasis herbs in the traditional Chinese medical systems. Despite their wide use in Chinese medicine, no report on system comparison on their chemical constituents is available so far. High-performance liquid chromatography coupled with diode array detector and electrospray ionization trap mass spectrometry (HPLC-DAD-ESI-Trap MS) technique was used for qualitative and quantitative analyses of the three Callicarpa herbs. Phenylpropanoid glycosides, flavonoids and organic acids were identified by comparing with reference standards or according to their MS/MS fragmentation behaviors. A total of 33 compounds were identified identified or tentatively identified, and 23 of them were reported from these herbs for the first time. Phenylpropanoid glycosides were featured in the three species with their types and contents presenting significant differences. Furthermore, quantitative analysis was conducted by determining four marker phenylpropanoid glycosides (forsythoside B (14), acteoside (15), poliumoside (19), isoacteoside (21)) and two flavonoids (luteolin (30), apigenin (32)). Three flavonoid glucuronides (luteolin-diglucuronide-glucuronide (5), luteolin-diglucuronide (12), apigenin-7-O-ß-glucuronide (24)) were semi-quantified according to their corresponding aglycones. The total contents of the nine major compounds in the three species varied significantly from 8.92 to 40.89 mg/g.

Widespread tannin intake via stimulants and masticatories, especially guarana, kola nut, betel vine, and accessories.

Tannins are increasingly recognized as dietary carcinogens and as antinutrients interfering with the system's full use of protein. Nevertheless, certain tannin-rich beverages, masticatories, and folk remedies, long utilized in African, Asiatic, Pacific, and Latin American countries, are now appearing in North American sundry shops and grocery stores. These include guarana (Paullinia cupana HBK.) from Brazil, kola nut (Cola nitida Schott & Endl. and C. acuminata Schott & Endl.) from West Africa, and betel nut (Areca catechu L.) from Malaya. The betel nut, or arecanut, has long been associated with oral and esophageal cancer because of its tannin content and the tannin contributed by the highly astringent cutch from Acacia catechu L. and Uncaria gambir Roxb. and the aromatic, astringent 'pan' (leaves of Piper betel L.) chewed with it. In addition to the constant recreational/social ingestion of these plant materials, they are much consumed as aphrodisiacs and medications. Guarana and kola nut enjoy great popularity in their native lands because they are also rich in caffeine, which serves as a stimulant. Research and popular education on the deleterious effects of excessive tannin intake could do much to reduce the heavy burden of early mortality and health care, especially in developing countries.