Article pubs.acs.org/JAFC
Protein-Precipitable Tannin in Wines from Vitis vinifera and Interspecific Hybrid Grapes (Vitis ssp.): Differences in Concentration, Extractability, and Cell Wall Binding Lindsay F. Springer and Gavin L. Sacks* Department of Food Science, Cornell University, 630 West North Street, Geneva, New York 14456, United States S Supporting Information *
ABSTRACT: Although they possess significant viticultural advantages, interspecific hybrid grapes (Vitis spp.) are reported to produce wine with lower tannin concentrations than European wine varieties (Vitis vinifera). However, extensive quantitative data on this phenomenon as well as mechanistic explanations for these differences are lacking. A survey of primarily commercial wines from the Finger Lakes American Viticultural Area (New York) using a protein precipitation method determined that hybridbased wines had >4-fold lower tannin concentrations than vinifera wines. To elucidate factors responsible for differences in wine tannin, 24 wines were produced from both red hybrid and vinifera cultivars under identical conditions. Lower wine tannin in French−American hybrid- than vinifera-based wines could be partially explained by lower grape tannin. However, experiments in which cell wall material was incubated with tannin indicated that cell wall binding may be of equal or greater importance in explaining lower wine tannin concentrations in hybrid-based wines. Subsequent characterization of cell wall material revealed that protein in flesh cell walls and, to a lesser extent, pectin in skin cell walls were correlated with cell wall binding. KEYWORDS: tannin, protein precipitation, interspecific hybrid, wine, cool climate
■
INTRODUCTION European winegrapes (Vitis vinifera, abbreviated as vinifera) are the major grape species used for wine production, representing 95% of the world winegrape market by tonnage.1 Because they evolved in a Mediterranean climate, vinifera grapes can be challenging to grow profitably in cool and humid climates due to their susceptibility to disease pressure and poor cold hardiness.2 Consequently, interspecific hybrid grapes (Vitis spp.) with vinifera and wild American Vitis species (e.g., rupestris, riparia) parentage have been developed, as these are suited for a wider range of climates and disease pressures. In response to the introduction of the phylloxera root louse to Europe during the late 19th and early 20th centuries, French− American hybrids were bred by directly crossing vinifera with wild American Vitis. These cultivars have largely been replaced in most European vineyards with vinifera grafted to resistant rootstocks, but continue to be cultivated for wine production elsewhere, particularly cool and humid regions of North America.2 Newer cultivars of hybrid grapes with a more complex selection history and vinifera backcrossings, referred to as neo-American hybrids, have subsequently been developed.3 Both French−American and neo-American hybrids can produce wines that exhibit organoleptic qualities atypical of vinifera wines and associated with wild Vitis. These generally undesirable traits can include excessive sourness due to high malic acid,4 excessive herbaceousness due to odorants such as methoxypyrazines,5 and, in crosses with V. labrusca parentage, “foxy”-smelling aromas due to odorants such as methyl anthranilate and o-aminoacetephonone.6,7 Another undesirable characteristic associated with red wines produced from hybrid grapes is low astringency, resulting in poor mouthfeel.8,9 The major compound class responsible for © 2014 American Chemical Society
astringency in red wines is the condensed tannins (proanthocyanidins).10 Condensed tannins are polymers of flavan-3-ol subunits, mainly catechin, epicatechin, epicatechin 3-O-gallate, and epigallocatechin, linked by C4−C8 or C4−C6 interflavan bonds. The mean degree of polymerization (mDP), subunit composition, and extractability during winemaking of tannins is tissue specific and, in most cases, cultivar dependent.11,12 Condensed tannins consisting of polymers of three or more subunits are able to bind to and precipitate salivary proteins or cross-link those on the oral mucosa surface, leading to an increase in friction in the oral cavity and the sensation of “astringency”, whereas monomers and dimers are reported to have low astringency and greater bitterness.13−15 In addition to affecting wine mouthfeel, tannins can also stabilize wine color through polymeric pigment formation via reaction with anthocyanins and other wine components.16 Because red wines with low tannin concentrations are correlated with lower bottle prices and consumer liking,17 selecting for grapes capable of producing higher tannin wines could be a valuable target for grape breeders. Recent studies, although limited in scope, have indicated that tannin concentrations are substantially lower in red wines produced from hybrid grapes than from vinifera and that these differences arise from grape composition rather than production practices. For example, using the Adams− Harbertson protein precipitation assay, tannin concentrations of
