Influence of Acidity and Extraction Time on the Recovery of Flavonoids from Grape Skin Pomace Optimized by Response Surface Methodology

Grape pomace is recognized as an economical source for the recovery of a large number of biologically active compounds, such as polyphenols. Grape pomace extracts can be successfully used as raw material for functional foods production, since they are generally recognized as safe for the food industry. This study aimed to quantify the amounts of recovered flavonoids (total flavonoids, proanthocyanidins, anthocyanins, and flavonols) from grape skin pomace (Vitis vinifera L. cv. Merlot) under conventional extraction with different acidities (0.5 % - 1 % HCl) and lengths of extraction time (30-60 minutes). The grand average values in this study were as follows: (i) proanthocyanidins 12.08[+ or -]0.25 mg CE [g.sup.-1] d.m., (ii) anthocyanins 2.17[+ or -]1.02 mg Mvd-3-glc [g.sup.-1] d.m., (iii) flavonols 7.73[+ or -]0.11 mg QE [g.sup.-1] d.m., and (iv) total flavonoids 36.28[+ or -]0.42 mg QE [g.sup.-1] d.m. The amounts of studied polyphenols generally increased with acidity and length of extraction time. This relation was more evident for flavonols and total flavonoids, while less clear for other examined phenolics.Key words:total flavonoids, proanthocyanidins, anthocyanins, flavonols, optimal extraction acidity/time, grape pomace skin extracts