Sample extraction
5.0 g of the different lyophilized samples were extracted by
overnight shaking on a mechanical shaker in the dark at RT.
The solvent used was 80 % aqueous methanol, as reported to be a better solvent for polyphenol extraction (Bonilla et al.
2003). The grape skin samples were extracted with 0.01 %
HCl in 80%aqueous methanol. The extracts were centrifuged
at 12,000 rpm for 15 min at 4 °C. The residues were
re-extracted (2 times, 3 h each) in similar conditions. The
filtrates were pooled and concentrated using a rotary evapo-
rator till themethanol gets completely evaporated. The residue
was dissolved in 5.0 ml distilled water, filtered through
0.45 μm filters and stored in different aliquots at −40 °C till
further analysis.