Extraction, distribution and characterisation of phenolic compounds and oil in grapeseeds

Five factors, extraction means, extraction repeats, extraction solvents, sample granularities, and grinding manners, were investigated and compared to optimise the extraction methods of phenolic compounds from grapeseed. Twenty minutes sequential sonication for three repeats was a preferred extraction means for assessment of phenolic content in grapeseed over three repeats 100-min sequential mechanical agitation. Methanol/water/HCl (70:29:1, v/v/v) was the best among the solvent compositions tested. Grinding granularity showed a significant (p = 0.05) effect on the yield of phenolic compounds when the sample was ground with a grinder and separated to different granularities by sieves. Grinding sample with mortar in liquid nitrogen could provide samples with uniform size and thus give a more consistent evaluation of phenolic compounds in grapeseed. Significant correlation coefficients (p < 0.01) among total phenols, total flavan-3-ols, and total proanthocyanidins contents in grapeseed extracts were observed. In addition, phenolic compounds and oil were very unevenly distributed in grapeseed as about 90% of phenolic compounds were observed in seed coat while about 60% of oil was in the endosperm and embryo.