Polyphenolic composition of grape stems

This study is focused on the study of polyphenolic compounds in grape stems as by-product of winemaking industry. Two white varieties of Gruner 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 Gruner 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.