Condensed tannins (CTs) are flavan-3-ol polymers that contribute critical organoleptic properties to an array of food products, including red wines and ciders.  In wine, predicting CT extraction from fruit tissues during processing is particularly difficult: the amount of CT in grapes is not directly related to the finished wine, supposedly due to CT binding grape-derived materials throughout the course of vinification.  To quantify the effect of CT binding to alcohol-insoluble grape materials, cell walls from the skins and flesh of interspecific hybrid and V.vinifera grapes were prepared and incubated in a model wine supplemented with a commercial tannin additive.  The [free/bound] partition coefficient (K) for tannin in skin cell wall material was 2-6 fold lower in French American Hybrid grape cultivars than V.vinifera, (ANOVA, p<0.05).  Flesh cell wall Ks were not significantly different, and values for V.vinifera were in agreement with previously published literature.  To investigate the contribution of wine soluble CT-binding, purified grape seed CT was added to select Vitis (spp.), interspecific hybrids and V.vinifera, at an addition rate of 150 mg/L catechin equivalents (CE).  After a timed incubation, samples were centrifuged and pelleted CT was resuspended and measured spectrophotometrically by ferric chloride addition.  Vitis (spp.) wines precipitated 74% of the CT addition, followed by interspecific hybrid wines (56%) and V.vinifera wines (34%).  CT pellets from interspecific hybrid and Vitis (spp.) wines were found to contain proteins, and were examined via SDS-PAGE and NanoLC-MS/MS, which identified three pathogenesis related proteins:  a VVTL1 precursor, class IV chitinase precursor, and �-1,3- glucanase.  Pathogenesis related proteins (PRPs) are well known for contributing to white wine haze, but their role in sequestering CT in interspecific hybrid red wine has not yet been evaluated.  We hypothesize that PRP quantities act to limit tannin extraction during red winemaking, particularly from disease-resistant interspecific hybrid grapes.

Glass ceiling on red wine condensed tannin: Limits imposed by soluble and insoluble tannin binding macromolecules

248th National Meeting (2014)

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