Comparative Polyphenolic Content of Grape Pomace Flours from ‘Fetească neagră’ and ‘Italian Riesling’ Cultivars

Abstract

Grape pomace is a waste from wine industry which pollutes the environment. This by-product is considered a potential source of polyphenols, which were proven to be powerful antioxidants or natural coloring agents. The aim of this study was to quantify total polyphenols, total anthocyanins content and some stilbenes in grape pomace seed, skin and mixed flours from ‘Fetească neagră’ (cultivar for red wines) and ‘Italian Riesling’ (cultivar for white wines), grown in Miniș-Măderat vineyard, Romania. Flours were obtained by natural drying and ulterior grinding. One-way ANOVA and Tukey’s post-hoc test were used.anthocyanins content was high in all the flours from ‘Fetească neagră’, with the highest concentration in skin flour (35.98 mg malvidin-3-O-glucoside/g dry weight). Stilbenes were also determined through HPLC methods. Cis-resveratrol was present in all forms of flour (0.90 to 10.14 μg/g dry weight), compared to its trans-isomer, which was not determined in ‘Italian Riesling’ seed and mixed flour. Trans-piceid was the most abundant stilbene and varied between 12.35 μg/g dry weight (‘Italian Riesling’ mixed flour) and 29.01 μg/g dry weight (‘Fetească neagră’ seed flour). The concentration of cis-piceid was similar among all forms of flour from ‘Italian Riesling’, while in ‘Fetească neagră’ seed flour (9.40 μg/g dry weight) it was present at a higher rate. Thus, results proved that ‘Fetească neagră’ flours are a better source of stilbenes than ‘Italian Riesling’ flours and seed flours from both varieties are richer in polyphenols than skin flours. Also, the concentration of anthocyanins in ‘Fetească neagră’ skin flour was high.