Recovery of catechins and proanthocyanidins from winery by-products using subcritical water extraction Original Research Article

The aim of this work was to study the recovery of catechins and proanthocyanidins from grape seeds obtained as by-products from wineries using superheated water. The effect of temperature in the extraction process was studied. For this purpose, five different assays were carried out. In three of them, samples were extracted once with water at 50, 100 and 150 °C, respectively, working at pressures around 1500 psi to keep the water in the liquid state. In the fourth, samples were treated twice using sequentially 50 and 100 °C, and in the fifth a three-stage sequential extraction was used at 50, 100 and 150 °C. The composition of the extracts obtained was performed by HPLC–DAD–MS. The results were compared with those obtained using conventional analytical extraction with methanol/water (75:25) at atmospheric pressure. The results showed that superheated water is a good solvent for extracting flavanols, in some cases better than methanol/water (75:25). In general, major recoveries were found when the material was submitted to three sequential extractions at 50, 100 and 150 °C, but selective extractions of compounds with different degrees of polymerisation can be achieved using one-step extraction at different temperatures. Better recoveries for flavanol dimers and trimers, showing higher antioxidant activity, were obtained using a single extraction at 150 °C. Furthermore, gallic acid, with antioxidant characteristics similar to the catechin and epicatechin monomers, is obtained in greater quantities by a single extraction at 150 °C. The greater the temperature the greater extraction of gallic acid, which reaches approximately 70% of the total of polyphenols extracted.