Grape Seed Oil: Supercritical Extraction, Chemical Analysis and Fractionation

Grape seed oil is a product resulting from the processing of grape marc. It is ever more appealing for the cosmetic and pharmaceutical industries: the pharmaceutical activities concern its antioxidant properties, due to the large content of unsaturated fatty acids. Grape seed oil could be extracted mechanically by pressing or chemically by means of solvents. Among the latter, supercritical CO2 represents an interesting possibility. The utilization of the supercritical technology to extract oil seems economically justified when obtaining an added-value final product, as could be grape seed oil enriched in polyunsaturated fatty acids. Actually, the supercritical extraction process could be coupled to a partial fractionation of the extracted matter based on the different solubility of the oil constituents. About the experimental extraction conditions, pressure ranged between 200-500 bar while the temperature was maintained constant at 40°C. This research aimed at investigating the possibility of a sequential separation of supercritical extracted oil into various fractions, and in analysing their chemical composition by using the modern chromatographic and spectroscopic methodologies. In particular, Nuclear Magnetic Resonance measurements (NMR) allowed us establishing not only the mean unsaturation degree, but also the molar ratio of every lipid class (glycerides, sterols, free fatty acids) present in every sample. Triacylglycerols (TAG) are by far the most abundant lipids in the oil and an accurate quali-quantitative profile of their distribution has been obtained by matching 1 Hand 13 C-NMR analysis both of the crude oil and of the fatty acid methyl esters (FAME), the latter obtained by direct transesterification of the crude oil. Before analysis, FAMEs have been purified by Silica-gel flash chromatography, identified by NMR and/or Mass spectroscopy and finally quantified by GC-FID. The results seem to indicate that the sequential fractionation of the oil during extraction is not effective in separating fractions of different composition: the differences in composition resulted almost insignificant.