Abstract
This study is focused on the study of polyphenolic compounds in grape stems as by-product of winemaking industry. Two white varieties of Grüner Veltliner and Sauvignon and two red varieties of Blauer Portugieser and Cabernet Moravia were selected for the study. Antioxidant activity, concentration of total polyphenols and concentration of individual phenolic compounds were determined. The results show a higher concentration of polyphenols and higher values of antioxidant activity in red varieties. The Blauer Portugieser variety contained the highest concentrations of syringic acid 1.346 mg.L-1, caffeic acid 20 mg.L-1, ferulic acid 1.192 mg.L-1, coumaric acid 3.231 mg.L-1, trans-resveratrol 14.195 mg.L-1, catechin 79.314 mg.L-1 and epicatechin 33.205 mg.L-1. Cabernet Moravia contained the highest concentration of protocatechuic acid 1.201 mg.L-1, the Sauvignon variety reached the highest concentration of gallic acid 4.015 mg.L-1 and hydroxybenzoic acid 0.076 mg.L-1. The highest values of alpha-amino acids were determined in the Blauer Portugieser variety 165.3 mg L-1 and the lowest in the Grüner Veltliner variety 33.3 mg L-1. The highest concentration of ammonia nitrogen was 214 mg L-1 for the Blauer Portugieser variety and the lowest concentration of ammonia nitrogen was measured in Cabernet Moravia 35.7 mg L-1.
Highlights
Grape polyphenolics vary in chemical structure and activity and may be fundamentally categorized into two major classes: flavonoids and nonflavonoids
Material The aim of the study was the evaluation of polyphenols as antioxidants in grape stems of the varieties Vitis vinifera L., namely the varieties Grüner Veltliner, Sauvignon blanc, Blauer Portugieser and Cabernet Moravia M-43
Results of the study by Domínguez-Perles (2014) suggested that optimal extraction of phenolic molecules may not reflect the highest antioxidant capacity. This may be explained by the potential for aqueous based solvents to contribute to solubilising a larger range of compounds, some of which may have little or no antioxidant activity (Anwar et al, 2013)
Summary
Grape polyphenolics vary in chemical structure and activity and may be fundamentally categorized into two major classes: flavonoids and nonflavonoids. Flavonoids, the most abundant polyphenolics in grape, are distributed throughout the peel, seed, and stem, and include anthocyanins, proanthocyanidins (procyanidins and prodelphinidins), and flavan-3-ols (Garrido-Banuelos et al, 2019). Hydroxycinnamic acids, the most abundant non-flavonoids in wine, include caftaric acid and coutaric acid (Lu and Foo, 1999). Most of these polyphenolic compounds occur as glycosylated derivatives in plants and foods and undergo enzymatic transformations in the gut before intestinal absorption (Bang et al, 2015). Bioactive polyphenolic compounds are partially extracted while the majority remain as glycosides embedded in the grape peel, pulp, or seed (Chafer et al, 2005). The amount of polyphenols released into the final wine product greatly depends on the fermentation process, suggesting that an insufficient extraction technique
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