Kinetic modeling of total polyphenol extraction from grape marc and characterization of the extracts

Solid-liquid extraction of total phenolic content (TPC) from grape marc was studied in the present work. Maximum TPC extraction was obtained at liquid-to-solid ratio of 50 mL of ethanol 50% per gram of dry marc. Extraction of TPC was, then, kinetically investigated and the applicability of several extraction models was evaluated. Pseudo-first order model was the best equation that represented extraction of TPC. Yields of extraction ranged from 11 to 22 mg GAE g(-1), with values of extraction rate between 0.040 and 0.1302 min(-1) in temperature range of 25-60 degrees C. Acid-hydrolyzed extract presented 55% of TPC from overall TPC in the grape marc. High concentration of condensed tannins, flavonoids, anthocyanins and tartaric esters were found strongly bonded to the plant matrix. The results also show that extracts present scavenging ABTS radicals, chelating capacities and reducing power, being most of the TPC with these characteristics cell wall bonded to grape marc matrix. (C) 2012 Elsevier B.V. All rights reserved.