Obtaining Multiple Coproducts from Red Grape Pomace via Anthocyanin Extraction and Biogas Production

Red grape pomace (RGP), a byproduct of red wine production, is an abundant food processing waste stream in California, rich in both anthocyanins, a class of red-blue pigments, and lignocellulose. Extraction of anthocyanins and biofuel production from RGP have been investigated independently, but no research has examined employing both strategies together for maximal valorization. In this study, anthocyanins were most effectively extracted from RGP at 80 °C. Convection- and vacuum-oven drying of the pomace were found to decrease anthocyanin yield, whereas lyophilization did not significantly affect yield. Fermentable sugars were successfully separated from the crude extract via solid-phase extraction. Ionic liquid pretreatment of RGP was determined to be a nonviable option for application to anaerobic digestion. Extraction reduced biomethane output, but supplementation with the aqueous fraction of the extract mitigated much of this difference, indicating sequential extraction and fractionation of anthocyanins from RGP can minimize the impact on biofuel yields.