Valorisation of grape pomace: Fractionation of bioactive flavan-3-ols by membrane processing

This work discusses the development of a process which aims at the production of high-value extracts, a food nutraceutical ingredient, rich in bioactive monomeric flavan-3-ols, by using low-value grape pomace as a raw material. As a first step, an extraction process using biocompatible solvents was optimised. The extract obtained was then fractionated using membrane technologies that allow obtaining target fractions of bioactive compounds and also to the recycle of the solvent. A detailed chemical characterisation of these fractions was also accomplished. The fractionation process achieved by dia-nanofiltration enabled to reject 40% of the monomeric flavan-3-ols in the permeate, with a low use of solvent (diafiltration volume of 2). The fractionated permeate was further concentrated by reverse osmosis, allowing for 90% re-use of the solvent. Considering this excellent result, higher dia-nanofiltration volumes may be used without additional solvent expenditure. Considering these results, a diafiltration volume of 5 may be used, leading to an estimated overall process rejection of 15% of monomeric flavan-3-ols.