Extraction of polyphenols from grape skins and defatted grape seeds using subcritical water: Experiments and modeling

Polyphenols were extracted from grape skins and defatted grape seeds (cultivar: Pinot Nero) by using subcritical water in a semi-continuous mode. Extractions were performed at a pressure of 10 MPa, at three different temperatures (80, 100 and 120 \ub0C) and with two water flows. For both skins and defatted seeds, total polyphenol (TP) yield significantly increased with temperature: for skins from 44.3 \ub1 0.4 to 77 \ub1 3 mg/g, while for defatted seeds from 44 \ub1 2 to 124 \ub1 1 mg/g when the temperature increased from 80 to 120 \ub0C. Importantly, TP yield decreased with flow rate at constant temperature. The extraction kinetics was simulated by a simple model from literature. The model adjustable parameters were calculated by best fitting procedures with experimental data: the model fitted the experimental kinetics curves in a satisfactory way, providing reference values for the adjustable parameters. The present research outlines the potentialities of using subcritical water for extracting valuable polyphenols from food processing by-products, and the effect of the operating conditions. Moreover, it proves that a very simple model from literature allows the interpretation of the extraction curves on the base of mass transfer and partition coefficients