Exploring the influence of S. cerevisiae mannoproteins on wine astringency and color: Impact of their polysaccharide part.

The impact of the polysaccharide moiety of mannoproteins (MPs) on the color and astringency of red wines was studied respectively through spectrophotometry and their impact on tannin interactions with BSA. To this end, MPs with conserved native structures from four different Saccharomyces cerevisiae strains were used: a Wild-Type strain (BY4742, WT) taken as reference, mutants ΔMnn4 (with no mannosyl-phosphorylation) and ΔMnn2 (linear N-glycosylation backbone), and a commercial enological strain. MPs affected tannin-BSA interactions by delaying aggregation kinetics.

Focus on the relationships between the cell wall composition in the extraction of anthocyanins and tannins from grape berries.

Concentrations of anthocyanins and tannins after extraction from berries in wines and from skin macerations in model solutions have been studied for two grape varieties, two maturation levels and two vintages berries. Characterization of the cell wall polysaccharides has also been performed, the classical method based on the analysis of the neutral sugars after depolymerization being completed by a comprehensive microarray polymer profiling (CoMPP). Extraction was lower in model solutions than in wines, with the same ranking: non acylated anthocyanins> tannins > p-coumaroylated anthocyanins.

Diffusion of phenolic compounds during a model maceration in winemaking: role of flesh and seeds.

Background: During red winemaking, diffusion of phenolic compounds from the grape berry cells into the liquid phase occurs simultaneously with the adsorption of the same compounds onto the pulp. In previous studies, we quantified the proportions of polyphenols diffusing from the skins and then assessed the amounts that can be fixed by the pulp. In this work, we added the impact of seeds, also present during vinification, by carrying out macerations in a model medium with the following berry compartments: skins, seeds, skins + seeds, skins + seeds + pulp.

Multi-method study of the impact of fermentation on the polyphenol composition and color of Grenache, Cinsault, and Syrah rosé wines.

Rosé wines show large color diversity, due to different phenolic pigment compositions. However, the mechanisms responsible for such diversity are poorly understood. The present work aimed at investigating the impact of fermentation on the color and composition of rosé wines made from Grenache, Cinsault, and Syrah grapes.

Structural characteristics of Saccharomyces cerevisiae mannoproteins: Impact of their polysaccharide part.

While they have many properties of interest in enology, the structure-function relationships of mannoproteins and the part played by their polysaccharide moiety are not yet well understood. Mannoproteins (MP) extracted with β-glucanase from a laboratory yeast strain (WT), two of its mutants (Mnn2 with unbranched N-glycosylated chains and Mnn4 without mannosyl-phosphorylation), and an enological strain (Com) were purified and thoroughly characterized. The protein moiety of the four MPs had the same amino acid composition.

Impact of the variety on the adsorption of anthocyanins and tannins on grape flesh cell walls.

Background: During winemaking, after extraction from the skins, anthocyanins and tannins adsorb onto the pulp flesh cell walls. The present study aimed to quantify the amounts adsorbed and their impact on wine composition, the impact of variety and ethanol on adsorption, and whether the presence of anthocyanins plays a role and impacts tannin adsorption.

Results: Anthocyanin and tannin fractions obtained by mimicking winemaking conditions were mixed with fresh flesh cell walls of two varieties: Carignan and Grenache.

Impact of grape variety, berry maturity and size on the extractability of skin polyphenols during model wine-like maceration experiments.

Background: Skin cell walls modulate anthocyanin and tannin extraction from grape skins. However, relationships between the composition of alcohol-insoluble cell wall solids (AIS) and extraction are still unclear. Our objectives were to characterize the impact of variety, berry size and ripeness on skin AIS composition (polysaccharides, proteins) and polyphenol extraction during maceration.

Wine Thermosensitive Proteins Adsorb First and Better on Bentonite during Fining: Practical Implications and Proposition of Alternative Heat Tests.

Bentonite fining is the most popular treatment used to remove proteins in white and rosé wines. The usual heat test used to adjust the bentonite dose consists of heating the wine during 30 min at 80 °C. At this temperature, all of the proteins are unfolded, and this can lead to an overestimation of the dose.

Fate of Anthocyanins and Proanthocyanidins during the Alcoholic Fermentation of Thermovinified Red Musts by Different Strains.

UV-visible spectrophotometry, size exclusion chromatography, and UHPLC-QqQ-MS were combined to evaluate the respective impacts of chemical changes and adsorption by yeasts on both proanthocyanidins (PA) and anthocyanins during the fermentation of a thermovinified red must by four yeast strains. Results evidenced a sharp decrease in anthocyanins (∼45%) and color intensity (∼50%), along with the formation of pyranoanthocyanins and flavanol-anthocyanin dimers related to yeast metabolism. However, the latter only accounted for 10% of anthocyanin losses.

p-Hydroxyphenyl-pyranoanthocyanins: An Experimental and Theoretical Investigation of Their Acid-Base Properties and Molecular Interactions.

The physicochemical properties of the wine pigments catechyl-pyranomalvidin-3--glucoside (PA1) and guaiacyl-pyranomalvidin-3--glucoside (PA2) are extensively revisited using ultraviolet (UV)-visible spectroscopy, dynamic light scattering (DLS) and quantum chemistry density functional theory (DFT) calculations. In mildly acidic aqueous solution, each cationic pigment undergoes regioselective deprotonation to form a single neutral quinonoid base and water addition appears negligible. Above pH = 4, both PA1 and PA2 become prone to aggregation, which is manifested by the slow build-up of broad absorption bands at longer wavelengths (λ ≥ 600 nm), followed in the case of PA2 by precipitation.

Protein/polysaccharide interactions and their impact on haze formation in white wines.

Proteins in white wines may aggregate and form hazes at room temperature. This was previously shown to be related to pH-induced conformational changes and to occur for pH <3.5.

Interactions of Condensed Tannins with Saccharomyces cerevisiae Yeast Cells and Cell Walls: Tannin Location by Microscopy.

Interactions between grape tannins/red wine polyphenols and yeast cells/cell walls was previously studied within the framework of red wine aging and the use of yeast-derived products as an alternative to aging on lees. Results evidenced a quite different behavior between whole cells (biomass grown to elaborate yeast-derived products, inactivated yeast, and yeast inactivated after autolysis) and yeast cell walls (obtained from mechanical disruption of the biomass). Briefly, whole cells exhibited a high capacity to irreversibly adsorb grape and wine tannins, whereas only weak interactions were observed for cell walls.

Condensed tannin changes induced by autoxidation: effect of the initial degree of polymerization and concentration.

Condensed tannins are a major class of polyphenols and play an important part in organoleptic properties of beverages. Because of their structure, they are chemically reactive. During food processing, reactions take place, leading to structural changes of the native structures to give modified tannins and pigments.

White wine proteins: how does the pH affect their conformation at room temperature?

Our studies focused on the determination of aggregation mechanisms of proteins occurring in wine at room temperature. Even if the wine pH range is narrow (2.8 to 3.

Stability of white wine proteins: combined effect of pH, ionic strength, and temperature on their aggregation.

Protein haze development in white wines is an unacceptable visual defect attributed to slow protein unfolding and aggregation. It is favored by wine exposure to excessive temperatures but can also develop in properly stored wines. In this study, the combined impact of pH (2.

Characterization of oxidized tannins: comparison of depolymerization methods, asymmetric flow field-flow fractionation and small-angle X-ray scattering.

Condensed tannins are a major class of plant polyphenols. They play an important part in the colour and taste of foods and beverages. Due to their chemical reactivity, tannins are not stable once extracted from plants.

Effects of ionic strength and sulfate upon thermal aggregation of grape chitinases and thaumatin-like proteins in a model system.

Consumers expect white wines to be clear. During the storage of wines, grape proteins can aggregate to form haze. These proteins, particularly chitinases and thaumatin-like proteins (TL-proteins), need to be removed, and this is done through adsorption by bentonite, an effective but inefficient wine-processing step.

Tannin oxidation: intra- versus intermolecular reactions.

Grape and apple condensed tannin fractions were autoxidized at high concentrations (5 g/L) in aqueous solutions and analyzed by thiolysis (depolymerization followed by HPLC analysis) and small angle X-ray scattering (SAXS). Structural parameters of native (unoxidized) tannin polymers were derived from SAXS according to the wormlike chain model: the length per monomer is 15 A, the length of the statistical segment 17 A, and the cross section of the macromolecule has a radius within the range 3-4.5 A.

Protein aggregation in white wines: influence of the temperature on aggregation kinetics and mechanisms.

High temperatures (typically 80 °C) are widely used to assess wine stability with regard to protein haze or to study mechanisms involved in their formation. Dynamic light scattering experiments were performed to follow aggregation kinetics and aggregate characteristics in white wines at different temperatures (30-70 °C). Aggregation was followed during heating and cooling to 25 °C.

Proline-rich salivary proteins have extended conformations.

Three basic proline-rich salivary proteins have been produced through the recombinant route. IB5 is a small basic proline-rich protein that is involved in the binding of plant tannins in the oral cavity. II-1 is a larger protein with a closely related backbone; it is glycosylated, and it is also able to bind plant tannins.

Aggregation of a proline-rich protein induced by epigallocatechin gallate and condensed tannins: effect of protein glycosylation.

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).

Colloidal dispersions of tannins in water-ethanol solutions.

The molecular interactions of grape-seed tannins dissolved in water-ethanol solutions have been studied through small angle neutron scattering, light scattering, and physical separation techniques. Through selective precipitation in different solvent mixtures, three populations of tannin macromolecules have been identified: T1 (2% of the total tannin), which forms colloidal particles when the ethanol content of the solvent is brought below phiA = 0.6; T2a (33% of the tannin), which phase-separates below phiA = 0.

Interactions between a non glycosylated human proline-rich protein and flavan-3-ols are affected by protein concentration and polyphenol/protein ratio.

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.

Shear-flow induced detachment of Saccharomyces cerevisiae from stainless steel: influence of yeast and solid surface properties.

The present study focused on the shear-induced detachment of Saccharomyces cerevisiae in adhesive contact with a 316L stainless steel surface using a shear stress flow chamber, with a view to determining the respective influence of the yeast surface properties and the support characteristics. The effect of cultivation of S. cerevisiae yeast cells on their subsequent detachment from the solid surface was particularly investigated.