Extraction of antioxidants from several berries pressing wastes using conventional and supercritical solvents

The solid waste generated in industrial berry juice production was considered as a low cost raw material for the extraction of natural antioxidants. Berries contain phenolic compounds with high antioxidant potential, including anthocyanins, proanthocyanidins, flavonols, catechins, benzoic and cinnamic acids. The solid residues generated from blueberry, cranberry and raspberry after pressing were extracted by conventional solvent extraction or by supercritical CO₂ (SC-CO₂) extraction. The effect of particle size and extraction time on the extraction yield, phenolic yield and phenolic content of the extracts produced by conventional solvents was assessed. Supercritical CO₂ extraction was performed during 2 h operating in the range 80-300 bar at 60 °C using 2.5 L CO₂/h. Maximum solubles yield of 5.20% were extracted from raspberry wastes at 200 bar, 3.89% from cranberry wastes at 250 bar and 1.4% from blueberry wastes at 200 bar. The highest phenolic content of the extracts was observed for blueberry pomace in the trap, with 9 grams of gallic acid equivalents per 100 g of extract. The ABTS (2, 2′-azino-bis-[3-ethylbenzotiazol-6-sulfonic acid]) and DPPH (α,α-diphenyl-β-picrylhydrazyl) radical scavenging capacity of the SC-CO₂ extracts was moderate in comparison with the activity of conventional solvent extracts.