Extraction of fatty acids from grape seed by superheated hexane

Superheated hexane extraction has been tested for obtaining fatty acids from grape seed and compared with conventional Soxhlet and hot hexane extractions. Seeds from grape residues from a winery were dried for 46 h at 105 °C, milled and sieved by particle size (d < 0.42 mm, 0.42 < d < 0.84 mm and d > 0.84 mm). An optimization study of influential variables on superheated hexane extraction (namely extraction time, temperature, pression, particle size and sample amount) was carried out by a multivariate approach. All the extracts were concentrated in a rotary evaporator and dried by adding 1 g of Na2SO4. Then, 2 ml of the dried extract were subjected to reaction with 1 ml of a 0.5 M solution of sodium methylate in methanol to obtain fatty acid methyl esters (FAMEs). After derivatization, FAMEs were quantified by GC-FID. The results show that the optimal conditions for superheated hexane extraction are: time extraction, 10 min; temperature, 80 °C; pressure, 40 bar; particle size, d < 0.42 mm; amount of sample, 0.4 g. Under these conditions, around 84% of the fatty acids (out of the amount obtained by Soxhlet extraction) is extracted. Comparison with Soxhlet and hot hexane extractions showed that the percentages of FAMEs are similar in all the extracts and they agree with the data in the bibliography.