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.

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.

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.

ABCG1 is involved in vitamin E efflux.

Vitamin E membrane transport has been shown to involve the cholesterol transporters SR-BI, ABCA1 and NPC1L1. Our aim was to investigate the possible participation of another cholesterol transporter in cellular vitamin E efflux: ABCG1. In Abcgl-deficient mice, vitamin E concentration was reduced in plasma lipoproteins whereas most tissues displayed a higher vitamin E content compared to wild-type mice. α- and γ-tocopherol efflux was increased in CHO cells overexpressing human ABCG1 compared to control cells. Conversely, α- and γ- tocopherol efflux was decreased in ABCG1-knockdown human cells (Hep3B hepatocytes and THP-1 macro- phages). Interestingly, α- and γ-tocopherol significantly downregulated ABCG1 and ABCA1 expression levels in Hep3B and THP-1, an effect confirmed in vivo in rats given vitamin E for 5 days. This was likely due to reduced LXR activation by oxysterols, as Hep3B cells and rat liver treated with vitamin E displayed a significantly reduced content in oxysterols compared to their respective controls. Overall, the present study reveals for the first time that ABCG1 is involved in cellular vitamin E efflux.