Abstract
Cold-hardy grape cultivars have become popular in northern regions. Wines from these cultivars are low in tannins and lighter in color compared to Vitis vinifera. The northern regions are striving to enhance desired ″full body″ and red color qualities in the wine produced from cold-hardy grapes. The objective of this study was to compare tannin and pigment content in skins and seeds of three cold-hardy red grape cultivars, at two time points, from two locations, using the Adams-Harbertson (A-H) assay. The A-H assay is based on protein precipitation and spectrophotometry. Total tannin concentrations detected in Frontenac, Marquette, and St. Croix berries, ranged from 0.29 to 0.66 mg/berry catechin equivalents (CE). Bitter seed tannins were most abundant in Marquette berries (0.54 ± 0.66 mg/berry CE). Softer skin tannins were most abundant in St. Croix berries (0.24 ± 0.19 mg/berry CE). Monomeric anthocyanins contributed to over 60% of the total color at pH 4.9 and were highest in St. Croix skins (74.21% of the total color at pH 4.9). Varying amounts of short polymeric pigments and long polymeric pigments were present in grape skins, indicating that pigmented tannins had already formed by harvest. This is the first evaluation of tannins and pigments in Frontenac, Marquette, and St. Croix berries.
Highlights
The phenolics in wine and grapes are a complex mixture
Since high levels of flavonols are important for wine quality, quantification of flavonols could be a way to Fermentation 2017, 3, 47; doi:10.3390/fermentation3030047
This paper focuses on an evaluation of tannins and pigments in three cold-hardy grapes, collected at two time points, in two vineyard locations
Summary
The phenolics in wine and grapes are a complex mixture. Grape phenolics can be classified into non-flavonoid and flavonoids. Both of these classes are reported to have antioxidant, anti-carcinogenic, and anti-inflammatory benefits to human health [1], but only flavonoid phenolics appear to influence perceived sensory attributes of grapes and wine [2]. Flavonoids are further categorized into four chemical classes including flavonols (e.g., quercetin), monomeric flavan-3-ols (e.g., catechins), tannins (condensed flavan-3-ols), and anthocyanins (e.g., pigment molecules such as malvidin-3-glucoside) [3]. Ultraviolet light exposure increases the level of flavonols in Pinot noir [4]. Since high levels of flavonols are important for wine quality, quantification of flavonols could be a way to Fermentation 2017, 3, 47; doi:10.3390/fermentation3030047 www.mdpi.com/journal/fermentation
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