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. RESULTS: Interestingly, the seeds alone released a rather high amount of polyphenols. As soon as they were in the presence of cell walls of skin/flesh, and/or anthocyanins, the concentration of seed tannins in the solution dropped dramatically, due to a combined effect of adsorption and/or precipitation and/or chemical reactions. The pulp certainly adsorbed tannins, but they also tended to shift the extraction equilibria, and it seems that more tannins could be extracted from skins and seeds when pulp was present. Polyphenol amounts extracted in model systems with skins + seeds + pulp were close to what was extracted in microvinification. CONCLUSION: These model experiments reflect relatively well extraction during microvinification experiments and highlight the respective impact of the grape berry's different compartments in the wine's final phenolic composition as well as some of the mechanisms involved. © 2022 Society of Chemical Industry.

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. Adsorption isotherms were measured. Adsorption of tannins was higher with Carignan than with Grenache and decreased when the ethanol content increased. In comparison, anthocyanins were adsorbed in small amounts, and their mixing with tannins had no impact on their adsorption. The differences were related to differences in pulp cell wall composition, particularly in terms of extensins and arabinans. CONCLUSION: Adsorption of tannins, which can reach 50% of the initial amount, depends on the pulp cell wall composition. This needs to be investigated further. © 2021 Society of Chemical Industry.

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. RESULTS: Grape skin composition and its impact on polyphenol extraction was compared for two varieties - Carignan and Grenache - with skins of berries sorted according to their size and density. Extractions were performed under model wine-like maceration conditions. Fresh skins had similar content of polymeric tannins, but strongly differed in their anthocyanin content (higher in Carignan and in the ripest berries) and composition (higher proportions in coumaroylated anthocyanins in Carignan). Anthocyanin extraction was proportionally much higher in Grenache, which was not just related to the Carignan's higher levels in coumaroylated anthocyanins. Chemical reactions decreased anthocyanin concentrations in solution for both varieties. Tannin extraction for Grenache was slightly higher and faster than for Carignan. Skin AISs differed slightly between the two varieties in their carbohydrate composition and protein content, but not between modalities. Polyphenol analyses in the precipitates evidenced at the end of the maceration and in residual skins highlighted differences between the two varieties and between berries with different ripeness. CONCLUSION: Structural information on the cell wall network and on its changes during maceration, along with a better understanding of the chemical reactions of anthocyanins and tannins, is needed to better relate grape and wine polyphenol composition. © 2020 Society of Chemical Industry.

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. Targeted MS analysis showed large varietal differences in must and wine compositions, with higher concentrations of anthocyanins and flavanols in Syrah. UV-visible spectrophotometry and size exclusion chromatography data indicated that Grenache and Cinsault musts contained oligomeric pigments derived from hydroxycinnamic acids and flavanols which were mostly lost during fermentation due to adsorption on lees. Syrah must color was mainly due to anthocyanins which were partly converted to derived pigments through reactions with yeast metabolites with limited color drop during fermentation. This work highlighted the impact of must composition, reflecting varietal characteristics, on changes occurring during fermentation and consequently wine color.

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. The polysaccharidic composition suggested a role of homogalacturonans, rhamnogalacturonans and extensins in the extraction process. A global explanation of the interactions between anthocyanins, tannins and polysaccharides is proposed.

Assessment of Megadenus holothuricola Rosén, 1910 (Eulimidae), an endoparasite of Holothuria mexicana Ludwig, 1875 (Holothuriidae) in the southern Gulf of Mexico and the description a new species.

As part of a study on holothurians from the southern Gulf of Mexico, some Holothuria mexicana Ludwig, 1875 were obtained for gut analysis. In two of them, a couple of eulimids were located inside the main tube of the respiratory tree. They were identified as Megadenus holothuricola Rosén, 1910, described from the Bahamas Islands, based on five specimens attached to the respiratory tree of H. mexicana. The original description was brief with few details, the type material is lost, and the species has not been found again. In this contribution, this species is confirmed for Campeche Bay, Mexico. The adult shell is globular to conical, transparent, thin, and fragile. Megadenus smithi sp. nov. from Palmyra Atoll, Central Pacific is described based on adult specimens. It differs from its congeneric species in its more robust shell, the pseudopallium does not cover the shell, and its short and contracted proboscis forms a thick disc. Further research on these eulimid parasites is now complicated in the southern Gulf of Mexico because of the holothurian population collapse due to over-exploitation of the fishery.

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. The rather short length of the statistical segment is an effect of the different location of interflavanol linkages, which cause a loss of orientational correlation between successive monomers. Oxidation created new bonds that were resistant to thiolysis, and, according to thiolysis, some of these new bonds were intramolecular. However, according to SAXS, oxidation at high tannin concentration caused the weight average degree of polymerization to increase, indicating that intermolecular reactions took place as well, creating larger macromolecules. In the case of the smaller grape seed tannins, these intermolecular reactions took place "end to end" leading to the formation of longer linear macromolecules, at least in the earlier stages of oxidation. In the case of the larger apple tannins, the SAXS patterns were characteristic of larger branched macromolecules. Accordingly, the intermolecular reactions were mainly "end to middle". This is in agreement with the higher probabilities of "end to middle" reactions arising from a higher ratio extension unit/terminal unit in the latter case.

Fate of Anthocyanins and Proanthocyanidins during the Alcoholic Fermentation of Thermovinified Red Musts by Different Saccharomyces cerevisiae 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. Comparison of spectrophotometry and phloroglucinolysis data underlined the involvement of PAs in chemical changes, related to yeast metabolites but also to direct reactions. Color losses during fermentation in this case study were mostly related to the formation of colorless compounds and to a decrease of copigmentation. Adsorption represented only a small proportion of pigment losses (∼5%) but a major part of those corresponding to total oligomeric/polymeric species, which were specifically involved. Only small differences could be evidenced between the four studied strains.

Isolation of Native Proanthocyanidins from Grapevine (Vitis vinifera) and Other Fruits in Aqueous Buffer.

Condensed tannins (also called proanthocyanidins) present in strategic tissues of fruits (outer pericarp and vascular bundles) were known as short polymers of flavan-3-ols. A pretreatment of the plant material (fruits from the grapevine, persimmon) with buffered ascorbic acid and Triton X-100 followed by acetone extraction provided native white fully depolymerizable tannins. Tannins are usually extracted with aqueous solvents and further purified, although artifactual oxidations occur, altering their physicochemical characteristics. Compared to artifactually oxidized tannins prepared according to standard protocols, white tannins (also called leukotannins) exhibit a higher degree of polymerization and a far lower polydispersity.

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. Average degrees of polymerization (DPs) determined by standard depolymerization methods become irrelevant, because bonds created from oxidation are uncleavable. Small-angle X-ray scattering was used to determine the conformation of native and autoxidized tannins and assess the impact of tannins initial DP and concentration on changes induced by autoxidation. Different behaviors were observed: (i) slight increase of the DP when tannins were oxidized in dilute solutions; (ii) increase of the DP with tannins in concentrated solutions, leading to the formation of longer linear chains or branched macromolecules depending on the initial DP.