Spent grape pomace: still a potential by-product?

The potential degradation grade of bioactive compounds caused by the drastic conditions of the distillation process towards grape pomace has been evaluated. Twenty-six phenolic compounds were identified and quantified in samples, including hydroxybenzoic acids (5), hydroxycinnamic acids (5), flavan-3-ols (5), flavanols (6), and anthocyanins (5) compounds. 2,2-Diphenyl-1-picrylhydrazyl radical (DPPH•) scavenging activity was evaluated to determine the antioxidant properties of different grape seeds and skins extracts. In addition, the oil contents and the fatty acid composition of grape seeds have been evaluated; the distillation process did not seem to significantly affect the fatty acid composition of extracted oils. Epicatechin gallate content was affected by distillation process; a positive increase was detected in both matrices with an average increment of about 23-fold for skins and 20-fold for seeds. In addition, anthocyanins content was strongly affected by distillation (generally 10-fold lower), proving that the high temperature applied on the matrix caused a both a degradation and a less extractability of these molecules in grape skin. The aim of this study was to demonstrate that not only the waste/by products from the winemaking industry can be exploited to obtain valuable compounds, but that these bioactive molecules - and even others resulting from the drastic conditions to which grape pomace is subjected for ethanol distillation - can be obtained from this exhausted matrices.