Towards multi-purpose valorisation of polyphenols from grape pomace: Pressurized liquid extraction coupled to purification by membrane processes

Abstract

Grape by-products (including skins, seeds, stems and vine shoots) are rich in health promoting polyphenols. Their extraction from winery waste and their following purification are of special interest to produce extracts with high added value compounds. Meanwhile, the growing concern over environmental problems associated with economic constraints, require the development of environmentally sustainable extraction technologies. The extraction using semi-continuous subcritical water, as a natural solvent at high temperature and high pressure a technology is promising “green” technology that is environmentally friendly, energy efficient and improve the extraction process in plant tissues. The suitable feature of subcritical water leaching agent is its capacity to decrease dielectric constant as a function of increase in temperature, allowing a better solubility of the compounds of interest. In our study subcritical water extraction of polyphenols from red and white grape pomace from Dunkelfelder, Cabernet Franc, Merlot, and Chardonnay was performed. In semi-continuous extraction lead to crude extracts rich in different families of polyphenols. A purification step prior to industrial usage is essential. Coupling subcritical water extraction with membrane processes, due to large array of flexibility, offers a solution for the purification and fractioning of the crude extracts. The combined effects of extraction temperature (from 60 to 200 °C), pressure (from 25 to 100 bar), flow rate (1 to 10 ml/min), sample mass (5, 70) were investigated and compared to traditional solvent extraction (1/1 ethanol/water). Optimal extraction conditions were found to be 150 C and 6ml/min irrelevant of the pressure used. These conditions produced crude extracts containing 130 mg/100g DW of anthocyanins (+61% compared to traditional methods of extraction) and 2077mg/100g DW procyanidins (+23%). Subsequently to realize the purification of the crude extract, several organic membranes having differential molecular weight cut off 0.45 μm up to 200 Da were tested. The results allow evaluating both the permeate flux through the membranes and the rejection rates of the major compounds found in the crude extract. The tested membranes have differential selectivity for polysacharrides, proteins, and different families phenolic compounds (pentamers, trimers, anthocyanin, and phenolic acids) with high purity (95%). Confirming the applicability of membrane separation for the fractionation and purification of pomace extracts. More research is needed to validate the industrial up scaling and the intended application of the produced extracts.