Extraction of polyphenols from grape marc by supercritical fluid extraction (SFE) and evaluation of their ‘bioavailability’ as dietary supplements

Abstract

In the winemaking process, several compounds that remain in the grape skins and seeds after the fermentation stage are bioactive-compounds (substances with potential beneficial effects on health) that can be extracted in order to recovery valuable substances with a high commercial value for the cosmetic, food (nutraceuticals) and pharmaceutical industries. The skins contain significant amounts of bioactive substances such as tannins (16-27%) and other polyphenolic compounds (2-6.5%) in particular, catechins, anthocyanins, proanthocyanins, quercetin , ellagic acid and resveratrol. The seeds, in addition to oil, contain approximately 60% of the polyphenols present in grape, in particular an high concentration of flavan-3-ols, catechin and epicatechin. Grape seed extracts are very potent antioxidants and exhibit numerous interesting pharmacologic activities The traditional extraction methods used for polyphenols from solid or semi-solid materials have been focused on methods, which use organic solvents. These methods are laborious and time consuming, promote degradation reactions, have low selectivity and/or low extraction yields. Moreover, these conventional techniques employ large amounts of toxic solvents. Some of these critical points could be over boost with Supercritical Fluid Extraction (SFE). The most used solvent in extraction with supercritical fluids is the CO2, which is economical, safe, non-toxic (it does not leave residues in extract) and reaches supercritical conditions easily (32°C and 74 bar). It is suitable for thermo-labile substances being the temperature of its critical point 32°C. In the supercritical phase it is selective towards apolar compounds or weakly polar, so it is necessary to add co-solvents (ethanol and water are the co-solvents used in food processing) in order to extract the polar compounds. Applying this technology the thermal and chemical degradation of the products, which are completely free from processing residues, is prevented, while the solvent power and selectivity can be easily adjusted from gas-like to liquid-like by changing the pressure and temperature of the extraction, making thus possible the fractionation of the extract. SFE is a Green Technology and this guarantees competitive advantage in conjunction with sustainable development. The extraction of phenolic compounds from grape marc using supercritical CO2 containing 15% ethanol–water mixture (57%, v/v) (EtW) as co-solvent, at 8, 10, 20 and 30 MPa/313.15 K suggested 8 MPa as the most suitable pressure. The evaluation of the ‘bioavailability’ of the grape-CO2 extracts so obtained was carried out . The ‘bioavailability’ is a key step in ensuring ‘bioefficacy’ of bioactive compounds when used as supplements because they need to be bioavailable in order to exert any beneficial effects on human health.