Toward the fingerprinting of wines: Cultivar-related patterns of polyphenolic constituents in Ontario wines

The concentrations of 15 polyphenols (the phenolic acids gentisic, vanillic, ferulic, m-coumaric, p-coumaric, caffeic, and gallic acid; the trihydroxystilbenes cis- and trans-resveratrol and cis- and trans-polydatin; and the flavonoids, catechin, epicatechin, quercetin, and morin) were measured in wines from a range of white (Chardonnay, Riesling, Seyval Blanc, Vidal) and red (Pinot Noir, Cabernet Sauvignon, Cabernet Franc, Merlot, Gamay Noir) cultivars grown in the viticultural region of Niagara, ON, Canada, to determine whether significant and characteristic differences in the content and relative patterns of individual polyphenols could be identified among the wines of various cultivars. An assay involving solid-phase extraction followed by derivatization and gas chromatography/mass spectrometry was used to quantify the polyphenols. Overlapping values between red and white wines were observed for gentisic, ferulic, p-coumaric, and caffeic acid; the concentrations of the other polyphenols were 5-20-fold higher in red wines, apart from m-coumaric acid and morin, which could not be detected in any of these wines. Ferulic acid was the highest of all phenolic acids in Riesling wine; in wines from the other three white grape cultivars, caffeic acid and p-coumaric acid were the highest, with caffeic acid being the highest in Chardonnay and Vidal wines and p-coumaric acid in those from Seyval Blanc. The latter had the lowest mean total phenolic acid concentration (0.035 mmol/L) compared with Chardonnay, Vidal, and Riesling (0.052, 0.066, and 0.075 mmol/L, respectively). The individual phenolic acids demonstrated a similar pattern among all of the red wines analyzed, with gallic acid being the highest and caffeic acid the second highest. Their mean total phenolic acid concentrations spanned a narrow range from 0.200 mmol/L (Gamay Noir) to 0.250 mmol/L (Pinot Noir). Of the hydroxystilbene components, Pinot Noir wines were notable in having by far the highest polydatin concentrations, whereas their concentrations of free resveratrol isomers were among the lowest in this study. Of the flavonoid components, Pinot Noir wines were highest in catechin and epicatechin concentrations, whereas wines from Cabernet Sauvignon that were lowest in the latter two flavonoids had the highest quercetin concentrations.