Hyperoxidation: influence of various oxygen supply levels on oxidation kinetics of phenolic compounds and wine quality

Chenin blanc, Mauzac and Chardonnay musts were hyperoxidized using three different oxygen levels fixed according to the maximum oxygen consumption capacity determined for each must. Phenolic composition of the control and oxidized musts and that of the corresponding wines were analyzed by HPLC. The wines were also submitted to sensory evaluation. Hyperoxidation hardly modified phenolic composition of Chenin blanc and Mauzac musts which were in fact almost totally oxidized after pressing. As well, it induced no change in wine quality in these two varieties. In Chardonnay musts, concentrations of caffeoyl and p-coumaroyl tartaric acid, 2-S-glutathionyl caffeoyl tartaric acid and catechin decreased with increasing oxygen supplies. Wines contained larger amounts of phenolic compounds than musts because part of the quinones formed during oxidation were reduced when sulfiting, especially for intemediate oxygen levels. Thus, sulfiting should be omitted or delayed to allow quinone condensation and maximum efficency of the hyperoxidation technique. Hyperoxidized Chardonnay wines were rated higher in quality and lower in color than the control

Procyanidin composition of Chardonnay, Mauzac and Grenache blanc grapes

Dimer procyanidins, galloylated or not, and trimers were analysed in three white grape varieties: Chardonnay, Mauzac and Grenache blanc. Procyanidins were extracted from the different components of the grape cluster (seeds, stems, skins and pulps) and then quantified by HPLC. Procyanidin B1 is the major component in stems and skins while procyanidin B2 is the major component in seeds

Age- and season-dependent pattern of flavonol glycosides in Cabernet Sauvignon grapevine leaves

Flavonols play key roles in many plant defense mechanisms, consequently they are frequently investigated as stress sensitive factors in relation to several oxidative processes. It is well known that grapevine (Vitis vinifera L.) can synthesize various flavonol glycosides in the leaves, however, very little information is available regarding their distribution along the cane at different leaf levels. In this work, taking into consideration of leaf position, the main flavonol glycosides of a red grapevine cultivar (Cabernet Sauvignon) were profiled and quantified by HPLC–DAD analysis. It was found that amount of four flavonol glycosides, namely, quercetin-3-O-galactoside, quercetin-3-O-glucoside, kaempferol-3-O-glucoside and kaempferol-3-O-glucuronide decreased towards the shoot tip. Since leaf age also decreases towards the shoot tip, the obtained results suggest that these compounds continuously formed by leaf aging, resulting in their accumulation in the older leaves. In contrast, quercetin-3-O-glucuronide (predominant form) and quercetin-3-O-rutinoside were not accumulated significantly by aging. We also pointed out that grapevine boosted the flavonol biosynthesis in September, and flavonol profile differed significantly in the two seasons. Our results contribute to the better understanding of the role of flavonols in the antioxidant defense system of grapevine

Toll-Like Receptor Ligands Induce Human T Cell Activation and Death, a Model for HIV Pathogenesis

Background: Recently, heightened systemic translocation of microbial products was found in persons with chronic HIV infection and this was linked to immune activation and CD4 + T cell homeostasis. Methodology: We examined here the effects of microbial Toll-like receptor (TLR) ligands on T cell activation in vitro. Conclusions/Findings: We show that exposure to TLR ligands results in activation of memory and effector CD4 + and CD8 + T cells. After exposure to each of 8 different ligands that activate TLRs 2, 3, 4, 5, 7, 8, and 9, CD8 + T cells are activated and gain expression of the C type lectin CD69 that may promote their retention in lymphoid tissues. In contrast, CD4 + T cells rarely increase CD69 expression but instead enter cell cycle. Despite activation and cell cycle entry, CD4 + T cells divide poorly and instead, disproportionately undergo activation-induced cell death. Systemic exposure to TLR agonists may therefore increase immune activation, effector cell sequestration in lymphoid tissues and T cell turnover. These events may contribute to the pathogenesis of immune dysfunction and CD4+ T cell losses in chronic infection with the human immunodeficiency virus

Relationship between the Sensory-Determined Astringency and the Flavanolic Composition of Red Wines

[EN] The relationship between the proanthocyanidin profile and the perceived astringency was assessed in 13 commercial Tempranillo red wines. The concentration and compositional information were obtained by liquid chromatography with diode array detection coupled to electrospray ionization mass spectrometry after acid-catalyzed depolymerization of wine proanthocyanidins in the presence of excess phloroglucinol. Statistical analysis of the results showed significant correlations between sensory and chemical determinations. Astringency was more affected by the subunit composition than by the total concentration or the average degree of polymerization of wine proanthocyanidins. Higher proportions of epicatechin (EC) subunits in extension positions and gallocatechin (GC) subunits in terminal positions were shown to increase astringency. On the contrary, the amount of epigallocatechin (EGC) in both extension and terminal positions was negatively correlated with the perceived astringency

Identification and functional characterization of cDNAs coding for hydroxybenzoate/hydroxycinnamate glucosyltransferases co-expressed with genes related to proanthocyanidin biosynthesis

Grape proanthocyanidins (PAs) play a major role in the organoleptic properties of wine. They are accumulated mainly in grape skin and seeds during the early stages of berry development. Despite the recent progress in the identification of genes involved in PA biosynthesis, the mechanisms involved in subunit condensation, galloylation, or fine regulation of the spatio-temporal composition of grape berries in PAs are still not elucidated. Two Myb transcription factors, VvMybPA1 and VvMybPA2, controlling the PA pathway have recently been identified and ectopically over-expressed in an homologous system. In addition to already known PA genes, three genes coding for glucosyltransferases were significantly differentially expressed between hairy roots over-expressing VvMybPA1 or VvMybPA2 and control lines. The involvement of these genes in PA biosynthesis metabolism is unclear. The three glucosyltransferases display high sequence similarities with other plant glucosyltransferases able to catalyse the formation of glucose esters, which are important intermediate actors for the synthesis of different phenolic compounds. Studies of the in vitro properties of these three enzymes (Km, Vmax, substrate specificity, pH sensitivity) were performed through production of recombinant proteins in E. coli and demonstrated that they are able to catalyse the formation of 1-O-acyl-Glc esters of phenolic acids but are not active on flavonoids and stilbenes. The transcripts are expressed in the early stages of grape berry development, mainly in the berry skins and seeds. The results presented here suggest that these enzymes could be involved in vivo in PA galloylation or in the synthesis of hydroxycinnamic esters

Procyanidin oligomers. A new method for 4->8 interflavan bond formation using C8-boronic acids and iterative oligomer synthesis through a boron-protection strategy

Interest in the synthesis of procyanidin (catechin or epicatechin) oligomers that contain the 4→8 interflavan linkage remains high, principally due to research into their health effects. A novel coupling utilising a C8-boronic acid as a directing group was developed in the synthesis of natural procyanidin B3 (i.e., 3,4-trans-(+)-catechin-4α→8-(+)- catechin dimer). The key interflavan bond was forged using a novel Lewis acid-promoted coupling of C4-ether 6 with C8-boronic acid 16 to provide the α-linked dimer with high diastereoselectivity. Through the use of a boron protecting group, the new coupling procedure was extended to the synthesis of a protected procyanidin trimer analogous to natural procyanidin C2. © 2011 Elsevier B.V. All rights reserved.Eric G. Dennis, David W. Jeffery, Martin R. Johnston, Michael V. Perkins, Paul A. Smit

Identification of structural features of condensed tannins that affect protein aggregation

A diverse panel of condensed tannins was used to resolve the confounding effects of size and subunit composition seen previously in tannin-protein interactions. Turbidimetry revealed that size in terms of mean degree of polymerisation (mDP) or average molecular weight (amw) was the most important tannin parameter. The smallest tannin with the relatively largest effect on protein aggregation had an mDP of ~7. The average size was significantly correlated with aggregation of bovine serum albumin, BSA (mDP: r=-0.916; amw: r=-0.925; p<0.01; df=27), and gelatin (mDP: r=-0.961; amw: r=-0.981; p<0.01; df=12). The procyanidin/prodelphinidin and cis-/trans-flavan-3-ol ratios gave no significant correlations. Tryptophan fluorescence quenching indicated that procyanidins and cis-flavan-3-ol units contributed most to the tannin interactions on the BSA surface and in the hydrophobic binding pocket (r=0.677; p<0.05; df=9 and r=0.887; p<0.01; df=9, respectively). Circular dichroism revealed that higher proportions of prodelphinidins decreased the apparent α-helix content (r=-0.941; p<0.01; df=5) and increased the apparent β-sheet content (r=0.916; p<0.05; df=5) of BSA

Impact of volatile phenols and their precursors on wine quality and control measures of Brettanomyces/Dekkera yeasts

Volatile phenols are aromatic compounds and one of the key molecules responsible for olfactory defects in wine. The yeast genus Brettanomyces is the only major microorganism that has the ability to covert hydroxycinnamic acids into important levels of these compounds, especially 4-ethylphenol and 4-ethylguaiacol, in red wine. When 4-ethylphenols reach concentrations greater than the sensory threshold, all wine’s organoleptic characteristics might be influenced or damaged. The aim of this literature review is to provide a better understanding of the physicochemical, biochemical, and metabolic factors that are related to the levels of p-coumaric acid and volatile phenols in wine. Then, this work summarizes the different methods used for controlling the presence of Brettanomyces in wine and the production of ethylphenols