Antioxidant compounds recovery from grape residues by a supercritical antisolvent assisted process

A process is proposed to selectively extract polyphenols and anthocyanins from lyophilized grape residues. The compounds of interest are first extracted from the vegetable matter, using a tartaric buffer to avoid extract degradation due to polyphenol oxidase, hydrolysis or esterification and to eliminate part of the interfering compounds (mainly sugars). Then, they are selectively adsorbed on a C18 column and desorbed using methanol. The methanolic solution is processed by supercritical antisolvent extraction (SAE) at various process conditions. The optimized result is a powderous, solventless precipitate that, in the case of Cannonau cultivar, contains 33 polyphenols and 7 anthocyanins. The overall content of polyphenols recovered is of 521 mg/kg and the total content of anthocyanins is of 15542 mg/kg of treated material. The most abundant compounds extracted are cathechin (113.9 mg/kg), epicathechin (96.9 mg/kg), epicathechin gallate (101.6 mg/kg) for polyphenols and malvin acetate (1304 mg/kg) and malvin cumarate (9256.9 mg/kg) for anthocyanins. SAE processing confirms to be very effective in producing solventless selective extracts, avoiding their degradation.