Grape by-products are rich in health promoting polyphenols. Their extraction from winery waste and their consequent 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 pressure is a promising “green” technology. The suitable feature of subcritical water as leaching agent is its capacity to decrease dielectric constant as a function of increase in temperature, allowing a better solubility for the compounds of interest. In our study subcritical water extraction of polyphenols from the red and white grape pomace of Dunkelfelder, Cabernet Franc, Merlot, and Chardonnay was performed. Semi-continuous extraction leads 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, 1000g) 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 268 mg/100g Dry Weight (DW) of anthocyanins (+23% compared to traditional methods of extraction) and 3406 mg/100g DW procyanidins (+34%). Subsequently, to complete the purification of the crude extract, several organic membranes having differential molecular weight cut off points ranging from 200 Da up to 0.45 μm 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 polysaccharides, proteins, and different families of phenolic compounds with high purity. 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.

Eco-innovative polyphenol extraction using subcritical water from red and white pomace, coupled with purification by membrane processes

250th National Meeting (2015)

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