Kinetic modelling for flavanol extraction from red grape (Vitis vinifera L.) pomace using aqueous organic acid solutions

Grape pomace is a food industry waste containing a high burden of antioxidant polyphenols and several methodologies have been developed for their efficient extraction. However, a sustainable and environmentally friendly process should involve recovery means composed of benign, non-toxic solvents. In this line, this study examined the extraction of flavanols, a particular class of functional polyphenols occurring in grape pomace, using aqueous acetic acid and citric solutions. The aim was to assess the role of acid concentration in the extraction yield, employing kinetics. The kinetic model established enabled the reliable comparison of the extraction efficiency of acetic acid and citric acid solutions as a function of acid concentration. The results showed that acetic acid solutions are more suitable for retrieving flavanols from grape pomace. Using a 4% (w/v) acetic acid solution, a maximum total flavanol yield of 80 μg catechin equivalents per g of dry pomace could be achieved.