Extraction of anthocyanins and flavan-3-ols from red grape pomace continuously by coupling hot water extraction with a modified expeller

• Extraction of polyphenol bioactive compounds from grape pomace
• Expeller modified for hot water extraction of pomace
• Recovery and characterization of anthocyanin/procyanidin compounds
• Replacement of organic solvents with high temperature water

A continuous aqueous-based extraction system was developed to extract anthocyanins and flavan-3-ols from red grape pomace. The system consisted of a modified midget expeller with multiple water injection ports which allowed the introduction of hot water into the expeller barrel. Variables tested were flow rate, water pre-bath temperature, expeller shaft temperature, shaft rotation speed, and sample moisture content (dried or crude). Compared to values obtained using conventional extraction, 41% of monomeric anthocyanins and 27% of total flavan-3-ols were extracted in dried samples under optimal conditions while 68% of monomeric anthocyanins and 58% of total flavan-3-ols were extracted in crude samples that were not dried. Antioxidant activity (ORAC assay) values of extracts from dried and crude pomace obtained under optimal conditions were 38 and 58%, respectively, compared to conventional extraction methods. However, high recoveries of the physiologically-active monomers catechin (145%) and epicatechin (104%) were recorded in crude extracts, compared with conventional organic solvent extraction. The described process offers an environmentally-compatible method for realizing a value-added product from the pomace waste stream that can be used as an antioxidant additive in food and nutraceutical formulations.