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1.
Binding of condensed tannins to salivary proteins is supposed to be involved in their astringency. First, complexes arising from the interaction of saliva from two individuals and tannins were studied. Then interaction mixture models containing purified saliva proteins were developed. The highest polymerized tannins predominantly precipitated together with the salivary proteins. Electrophoresis of proteins in combination with thiolysis analysis of tannins indicated proline-rich protein (PRP)-polyphenol complexes in precipitated fractions and also in the soluble ones with individual differences. Individual salivas exhibiting different protein patterns were discriminated with regard to their ability to interact with tannins. From binding studies with purified classes of salivary proteins, interactions were shown to depend on the nature of the protein, in particular on their glycosylation state. For low concentrations of tannins, glycosylated PRP-tannin interactions led to complexes that remained soluble, whereas those arising from nonglycosylated PRP-tannin interactions were precipitated. This finding could indicate that under physiological conditions, complexes involving glycosylated proteins maintain part of the lubrication of the oral cavity, whereas tannin trapping leads to a lower astringency perception.  相似文献   

2.
Thiolysis of a wine tannin fraction yielded trihydroxylated flavanol units (as previously observed in grape skins) in addition to the well-known procyanidins (dihydroxylated units), usually described in the literature for grape condensed tannins. To determine how they occur in condensed tannins, the wine fraction was analyzed by liquid chromatography coupled to electrospray ionization mass spectrometry. Thus, various series of ion peaks containing a variable number of trihydroxylated units were detected as monocharged ions from dimers up to pentamers. From pentamers, oligomers were found as doubly charged ions. Heptamer species corresponded to the highest mass detected. These results showed that wine condensed tannins consist of, besides procyanidins, mixed tri- and dihydroxylated flavanol units and also of pure trihydroxylated flavanol units. These new data should be taken into account to interpret organoleptic properties of wines.  相似文献   

3.
Astringency is one of the most important organoleptic qualities of numerous beverages, including red wines. It is generally thought to originate from interactions between tannins and salivary proline-rich proteins (PRPs). In this work interactions between a glycosylated PRP, called II-1, and flavan-3-ols were studied in aqueous solutions and at a colloidal level, by dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS). The flavan-3-ols were a monomer, epigallocatechin gallate (EGCG), and polymerized flavan-3-ol fractions extracted from grape seeds. In aqueous solutions containing EGCG and protein II-1, protein aggregation took place when protein concentration and the EGCG/protein ratio exceeded a threshold. The aggregates had a small size, comparable with the dimensions of protein monomers, and formed stable dispersions (no phase separation). Most proteins remained free in solution. This behavior is in sharp contrast with the phase separation observed for nonglycoslated PRP in the same conditions. Moreover, this slight aggregation of II-I in the presence of EGCG was disrupted by the addition of 12% ethanol. Increasing the flavan-3-ol molecular weight strongly enhanced II-I/tannin aggregation: the threshold was at a lower protein concentration (0.2 mg/mL) and a lower tannin/protein ratio. Still, in most cases, and in contrast with that observed with a nonglycosylated PRP, the aggregates remained of discrete size and stable. Only at low ethanol content (2%) did the addition of tannin polymers finally lead to phase separation, which occurred when the molar ratio of tannins to proteins exceeded 12. This systematic effect of ethanol confirmed the strong effect of cosolvents on protein/tannin interactions.  相似文献   

4.
Condensed tannins are a group of polyphenols that are associated with the astringency sensation, as they readily interact and precipitate salivary proteins. As this interaction is affected by carbohydrates, the aim of this work was to study the effect of some carbohydrates used in the food industry [arabic gum (AG), pectin, and poligalacturonic acid (PGA)] on the salivary proteins/grape seed procyanidins interaction. This was assessed monitoring the salivary proteins that remain soluble in the presence of condensed tannins with the addition of carbohydrates (HPLC) and analysis of the respective precipitates (SDS-PAGE). The results show that pectin was the most efficient in inhibiting protein/tannin precipitation, followed by AG and PGA. The results suggest that pectin and PGA exert their effect by formation of a ternary complex protein/polyphenol/carbohydrate, while AG competes with proteins for tannin binding (competition mechanism). The results also point out that both hydrophilic and hydrophobic interactions are important for the carbohydrate effects.  相似文献   

5.
Our aim was to compare enzyme activities (tannase, polyphenol oxidase and protease) with concentrations of tannins and their ability to precipitate proteins in the litter layer and the humus layer under silver birch (Betula pendula Roth.) and Norway spruce (Picea abies L.). We also estimated the influence of these enzymes on protein-tannin complexes and the influence of tannins on proteolytic activity. The study site was a tree species experiment in Eno, middle-eastern Finland, having three replicated plots dominated by 42-year-old silver birch and Norway spruce. Our hypotheses were (1) tree species and soil layer have an influence on tannin concentrations and enzyme activities, (2) that tannin and protein concentrations in soil organic horizon are positively correlated with enzyme activities and (3) that the enzymes studied have the ability to degrade tannin-protein complexes and that tannins can inhibit proteolytic activity. Concentrations of total tannins and hydrolysable tannins, and tannase and proteolytic activities were higher in the humus layer than in the litter layer. In general the highest values of concentrations of total tannins and hydrolysable tannins and enzyme activities were obtained for the birch humus layer, but the concentrations of condensed tannins and proteins were highest in the litter layer and under spruce. A strong correlation between substrate concentration and enzyme activity was found between hydrolysable tannins and tannase activity. Polyphenol oxidase showed similar activities in both layers. To study the influence of enzymes on protein-tannin complex we synthesized such complexes using bovine serum albumin and either condensed tannins from silver birch and Norway spruce needles or a hydrolysable tannin, tannic acid. Studies with commercial enzymes and enzymes extracted from the soil showed some decrease in tannin concentration of the tannin-protein complex over time, but surprisingly, only a negligible decrease in protein concentration. Complexes of protein with condensed tannins were more recalcitrant than tannic acid-protein complexes. Tannins, depending on the concentration and chemical structure, tended to inhibit proteolytic activity. Our results indicate that protein-tannin complexes are relatively recalcitrant since the enzymes studied here do not effectively release protein from the complexes. Also proteolytic activity and the concentration of extractable proteins seem to be low in soil. However, tannin-degrading enzymes showed high activities.  相似文献   

6.
Tannins are well-known food polyphenols that interact with proteins, namely, salivary proteins. This interaction is an important factor in relation to their bioavailability and is considered the basis of several important properties of tannins, namely, the development of astringency. It has been generally accepted that astringency is due to the tannin-induced complexation and/or precipitation of salivary proline-rich proteins (PRPs) in the oral cavity. However, this complexation is thought to provide protection against dietary tannins. Neverthless, there is no concrete evidence and agreement about which PRP families (acidic, basic, and glycosylated) are responsible for the interaction with condensed tannins. In the present work, human saliva was isolated, and the proteins existing in saliva were characterized by chromatographic and proteomic approaches (HPLC-DAD, ESI-MS, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and MALDI-TOF). These approaches were also adapted to study the affinity of the different families of salivary proteins to condensed tannins by the interaction of saliva with grape seed procyanidins. The results obtained when all the main families of salivary proteins are present in a competitive assay, like in the oral cavity, demonstrate that condensed tannins interact first with acidic PRPs and statherin and thereafter with histatins, glycosylated PRPs, and bPRPs.  相似文献   

7.
Interactions of grape seed tannins with salivary proteins   总被引：3，自引：0，他引：3  
To evaluate the amount and type of condensed tannins binding salivary proteins, which are supposed to be involved in astringent sensation, model systems allowing further analyses of proteins and condensed tannins were developed. The precipitates formed after addition of grape seed tannins to salivary proteins indicate that a binding interaction occurs. Dissociation of insoluble complexes was achieved by sodium dodecyl sulfate treatment. Thiolysis reaction allowed the quantification and characterization of proanthocyanidins on both the resulting pellet and the supernatant. Binding proteins were investigated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The higher polymerized tannins predominantly precipitated together with the salivary proteins. The condensed tannins remaining in solution were low molecular weight polymers.  相似文献   

8.
Interactions between salivary proline-rich proteins and tannins are involved in astringency, which is one of the most important organoleptic sensations perceived when drinking wine or tea. This work aimed to study interactions between a recombinant human salivary proline-rich protein, IB-5, and a flavan-3-ol monomer, epigallocatechin gallate (EGCG). IB-5 presented the characteristics of natively unfolded proteins. Interactions were studied by dynamic light scattering, isothermal titration microcalorimetry, and circular dichroism. The interaction mechanism was dependent on protein concentration. At low concentrations, a three-stage mechanism was evidenced. Saturation of the interaction sites (first stage) was followed by protein aggregation into metastable colloids at higher EGCG/protein ratios (second stage). Further increasing this ratio led to haze formation (third stage). At low ratios, a disorder-to-order transition of IB-5 structure upon binding was evidenced. At high protein concentrations, direct bridging between proteins and EGCG was observed, resulting in significantly lower aggregation and turbidity thresholds.  相似文献   

9.
In this study, three different phenolic (anthocyanin, other flavonoid, and phenolic acid) fractions from wine and a condensed tannin preparation from sorghum were tested for their effects on melanogenesis of normal cells and growth of human melanoma cells. The wine phenolic fractions decreased melanogenic activity (tyrosinase activity) at concentrations that resulted in a slight variation in melanocyte viability. Sorghum tannins, however, increased melanogenic activity, although no increase was found in total melanin at the concentrations that least affect melanocyte viability. Incubation of human melanoma cells with the wine fractions and sorghum tannins resulted in a decrease in colony formation, although the effect was not dose dependent in all cases. These results suggest that all of these phenolic fractions have potential as therapeutic agents in the treatments of human melanoma, although the mechanisms by which cellular toxicity is effected seem to be different among the fractions.  相似文献   

10.
A simple, fast, and more selective approach is presented in this study for the identification of haze-active proteins. Grape seed proteins were unfolded by 1% SDS and then interacted with different amounts of tannin at 4 degrees C, followed by gel electrophoresis. It was found that the intensity of the band at 45 kDa was decreased as tannins increased. The amino acid composition of this isolated 45-kDa protein was higher in proline (9.49%) than the average proline content of total grape seed proteins (4.85%). To verify the selectivity of the proposed method, a globular protein (bovine serum albumin, BSA) and a proline-rich protein (gelatin) were selected and used in the model system. As expected, gelatin was removed as it reacted with the increasing added tannins, whereas BSA did not. These results showed that it is possible to identify haze-active proteins by modulating the accessibility of protein to tannins, suggesting this new method can be used by the beverage industry to trouble-shoot haze problems and for quality control.  相似文献   

11.
Quantification of red grape tannin and red wine tannin using the methyl cellulose precipitable (MCP) tannin assay and the Adams-Harbertson (A-H) tannin assay were investigated. The study allowed for direct comparison between the repeatability of the assays and for the assessment of other practical considerations such as time efficiency, ease of practice, and throughput, and assessed the relationships between tannin quantification by both analytical techniques. A strong correlation between the two analytical techniques was observed when quantifying grape tannin (r(2) = 0.96), and a good correlation was observed for wine tannins (r(2) = 0.80). However, significant differences in the reported tannin values for the analytical techniques were observed (approximately 3-fold). To explore potential reasons for the difference, investigations were undertaken to determine how several variables influenced the final tannin quantification for both assays. These variables included differences in the amount of tannin precipitated (monitored by HPLC), assay matrix variables, and the monomers used to report the final values. The relationship between tannin quantification and wine astringency was assessed for the MCP and A-H tannin assays, and both showed strong correlations with perceived wine astringency (r(2) = 0.83 and r(2) = 0.90, respectively). The work described here gives guidance to those wanting to understand how the values between the two assays relate; however, a conclusive explanation for the differences in values between the MCP and A-H tannin assays remains unclear, and further work in this area is required.  相似文献   

12.
Polyphenol-rich extracts from soft fruits were tested for their ability to inhibit alpha-amylase and alpha-glucosidase. All extracts tested caused some inhibition of alpha-amylase, but there was a 10-fold difference between the least and most effective extracts. Strawberry and raspberry extracts were more effective alpha-amylase inhibitors than blueberry, blackcurrant, or red cabbage. Conversely, alpha-glucosidase was more readily inhibited by blueberry and blackcurrant extracts. The extent of inhibition of alpha-glucosidase was related to their anthocyanin content. For example, blueberry and blackcurrant extracts, which have the highest anthocyanin content, were the most effective inhibitors of alpha-glucosidase. The extracts most effective in inhibiting alpha-amylase (strawberry and raspberry) contain appreciable amounts of soluble tannins. Other tannin-rich extracts (red grape, red wine, and green tea) were also effective inhibitors of alpha-amylase. Indeed, removing tannins from strawberry extracts with gelatin also removed inhibition. Fractionation of raspberry extracts on Sephadex LH-20 produced an unbound fraction enriched in anthocyanins and a bound fraction enriched in tannin-like polyphenols. The unbound anthocyanin-enriched fraction was more effective against alpha-glucosidase than the original extract, whereas the alpha-amylase inhibitors were concentrated in the bound fraction. The LH-20 bound sample was separated by preparative HPLC, and fractions were assayed for inhibition of alpha-amylase. The inhibitory components were identified as ellagitannins using LC-MS-MS. This study suggests that different polyphenolic components of fruits may influence different steps in starch digestion in a synergistic manner.  相似文献   

13.
Tannins are purported to be an important factor controlling nitrogen cycling in forest ecosystems, and the ability of tannins to bind proteins in protein-tannin complexes is thought to be the primary mechanism responsible for these effects. In this study, we examined the influence of well-characterized tannins purified from five different plant species on C and N dynamics of a forest soil A horizon. Tannic acid, a commonly used and commercially available hydrolyzable tannin (HT), and cellulose were also included for comparison. With the exception of tannins from huckleberry (Vaccinium ovatum), the amendments increased respiration 1.4-4.0 fold, indicating that they were acting as a microbial C source. Tannic acid was significantly more labile than the five purified tannins examined in this study. All treatments decreased net N mineralization substantially, through greater N immobilization and decreased mineralization. The six tannins inhibited gross ammonification rates significantly more than cellulose. This suggests that added tannins had effects in addition to serving as an alternative C source. Tannins purified from Bishop pine (Pinus muricata) were the only tannins that significantly inhibited potential gross nitrification rates, however, rates were low even in the control soil making it difficult to detect any inhibition. Differences in tannin structure such as condensed versus HTs and the hydroxylation pattern of the condensed tannin B-ring likely explain differences observed among the tannin treatments. Contrary to other studies, we did not find that condensed tannins were more labile and less inhibitory than HTs, nor that shorter chained tannins were more labile than longer chained tannins. In addition to supporting the hypothesis that reduced N availability in the presence of tannins is caused by complexation reactions, our data suggests tannins act as a labile C source leading to increased N immobilization.  相似文献   

14.
For two successive years, cell walls were isolated from the internal part of skin cells of Vitis vinifera L. cv. Cabernet Sauvignon grape berries grown in a vineyard. Procyanidin localization and composition were determined over the course of development. Tannins were mainly localized in the inner cell fraction, due to their biosynthesis and storage. Cell wall tannins always exhibited a higher mean degree of polymerization as compared to the internal cell fraction, which had a constant mDP. The mDP of cell wall tannins also tended to increase at the end of maturation. Our results suggest tannin polymerization near the cell wall but an aggregation in the vacuole during growth. The tannin composition was typical of skins, and small differences were noted between the two cell parts. Surprisingly, epigallocatechin-3-gallate was also detected, although in a very small amount. Epicatechin was present in significant proportions in both fractions, especially as an extension subunit, while epigallocatechin was likewise abundant, also as a terminal subunit. Last, procyanidin composition and organization seemed to be characteristic of the Cabernet Sauvignon variety.  相似文献   

15.
Four vineyards from the eastern foot of Helan Mountain within the same climate classification, where the planted grapes were 4-year-old Cabernet Sauvignon, were selected for investigating the difference in grape and wine properties. Results showed that the grapes of Lilan vineyard had a higher sugar content and sugar–acid ratio than Huida, Yuquan and Zhihuiyuanshi vineyards. The grapes of Zhihuiyuanshi vineyard had the highest tannin and total phenols content. Concerning the wines, the wine of Yuquan vineyard had low pH but had a great ageing potential, and wine of Zhihuiyuanshi vineyard had highest tone, chroma, tannins, total phenols and alcohol content than other vineyards. Soil pH was positively correlated with anthocyanins in the grapes and negatively correlated with total acid in wine. The microbial biomass carbon (MBC) was correlated with the anthocyanins in grape. Microbial biomass nitrogen (MBN) was positively correlated with soluble solid in grapes, and positively correlated with tannin and total phenols in the wine. The MBC/MBN ratio was negatively correlated with tone in the wine. Our findings indicate that adjusting soil pH and choosing microbial fertiliser with high soil microbial carbon and nitrogen nutrients are effective ways to improve the quality of regional grapes and wine.  相似文献   

16.
气象条件对酿酒葡萄若干品质因子的影响   总被引：8，自引：1，他引：8  
根据2004-2005年北方6省酿酒葡萄主要产区葡萄取样和宁夏芦花台园艺场田间试验资料，分析了影响酿酒葡萄主要品质因子总糖、总酸、pH值和单宁积累的气象因子和影响时段，并建立了关系模式，提出了影响酿酒葡萄品质的定量气象指标。研究结果表明：酿酒葡萄品质与气象条件密切相关，主要影响因子是降水量、积温和气温日较差等。影响酿酒葡萄品质形成的关键时期是7-8月（幼果膨大-果实着色期），其次是果实着色期-成熟期。7—8月降水量和水热系数对酿酒葡萄总糖含量的影响最大，7-8〉130mm，K7-8〉1．62时，总糖含量不能达到170g／L（酿优质酒所需最低糖度）。酿酒葡萄总酸含量与果实采收前一个月水热系数呈幂指数关系，随水热系数增加，含酸量缓慢增加。因此，要使酿酒葡萄果实中酸含量达到5～6g／L，则果实采收前一个月的水热系数应在0．12～0．63。酿酒葡萄中单宁含量与开花-成熟期积温、8月平均气温、9月l日到果实采收期日较差和采收前一个月平均最低气温呈指数关系，与8月日照时数呈二次曲线关系。酿酒葡萄果实的pH值随开花-成熟期平均最高气温和果实膨大期蒸发量的增加而增加。  相似文献   

17.
Proline-rich proteins (PRP) in human parotid saliva have a high affinity for dietary polyphenolic compounds (tannins), forming stable complexes that may modulate the biological and nutritional properties of the tannin. The formation of such complexes may also have an important role in the modulation or promotion of the sensation of oral astringency perceived when tannin-rich foods and beverages are consumed. The major classes of PRP (acidic, basic, and glycosylated) have been isolated from human saliva, and the relative binding affinities of a series of hydrolyzable tannins, which are found in a number of plant-derived foods and beverages, to these PRP classes have been determined using a competition assay. All of the classes of PRP have a high capacity for hydrolyzable tannins. Within the narrow range of binding affinities exhibited, structure/binding relationships with the levels of tannin galloylation, hexahydroxydiphenoyl esterification, and degree of polymerization were identified. No individual class of human salivary PRP appears to have an exclusive affinity for a particular type of hydrolyzable tannin.  相似文献   

18.
Cell walls were isolated from seeds of grape berries (Vitis vinifera L.), and proanthocyanidin composition was determined over the course of ripening for different levels of vine water status. During the ripening period the tannins from the cell walls were always more polymerized than those from the inner part of the cell. At maturity this difference becomes more significant compared to véraison, due to a significant increase in the mean degree of polymerization of the cell wall tannins. The tannin composition was typical of grape seed tannins and was quite similar in the two cell fractions studied, but the epicatechin gallate proportion was significantly higher in the cell wall fraction. There were no significant effects of water deficit on composition and polymerization of seed tannins.  相似文献   

19.
The ability of all major human salivary histatins to precipitate condensed tannin was demonstrated, and it was found that histatins 3 and 5 share the same condensed tannin-binding region but less tannin bound to histatin 1. The condensed tannin-binding region of histatin 5 includes both the N- and the C-terminal parts, although more tannin binding occurs in the C-terminal region. Epigallocatechin gallate (EGCG) showed similar binding characteristics as condensed tannin, but much less EGCG was precipitated. Pentagalloyl glucose (PGG) was precipitated equally well by histatins 1, 3, and 5 and bound equally well to the N- and C-terminal regions of histatin 5. In contrast to condensed tannin, cleaving histatin 5 into N- and C-terminal fragments increased their ability to precipitate PGG. Together, these results show a number of differences in the nature of interaction of histatins with condensed tannin, EGCG, and PGG. Most of the condensed tannin-protein complexes remained insoluble under conditions similar to those in the stomach and the small intestine, suggesting that histatins may act as a defense against dietary tannin in humans.  相似文献   

20.
In the first part of this work, the analysis of the polyphenolic compounds remaining in the wine after different contact times with yeast lees during simulation of red wine aging was undertaken. To achieve a more precise view of the wine polyphenols adsorbed on lees during red wine aging and to establish a clear balance between adsorbed and remnant polyphenol compounds, the specific analysis of the chemical composition of the adsorbed polyphenolic compounds (condensed tannins and anthocyanins) after their partial desorbtion from yeast lees by denaturation treatments was realized in the second part of the study. The total recovery of polyphenol compounds from yeast lees was not complete, since a rather important part of the initial wine colored polyphenols, especially those with a dominant blue color component, remained strongly adsorbed on yeast lees, as monitored by color tristimulus and reflectance spectra measurements. All anthocyanins were recovered at a rather high percentage (about 62%), and it was demonstrated that they were not adsorbed in relation with their sole polarity. Very few monomeric phenolic compounds were extracted from yeast lees. With the use of drastic denaturing treatments, the total recovery of condensed tannins reached 83%. Such tannins extracted from yeast lees exhibited very high polymeric size and a rather high percentage of galloylated residues by comparison with initial wine tannins, indicating that nonpolar tannins were preferentially desorbed from yeast lees by the extraction treatments.  相似文献   

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