A comparative study on different extraction techniques to recover red grape pomace polyphenols from vinification byproducts

• Water:ethanol is a suitable solvent for the recovery of polyphenols from GP.
• Water:ethanol UAE extracts were rich in anthocyanins, flavonols and flavan-3-ols.
• Air drying is an effective pretreatment for the recovery of polyphenols from GP.
• Malvidin-3-O-glucoside, quercetin and myricetin were identified in the GP extracts.

In this study, Agiorgitico red grape pomace byproducts were dehydrated by air drying and accelerated solar drying and sequentially extracted by three different extraction methods using water, water:ethanol (1:1) and ethanol as solvents. The methods include microwave assisted (MAE) and ultrasound assisted extraction (UAE) and the conventional Soxhlet extraction (SE). The efficiency and selectivity of drying and extraction processes were determined in terms of extraction yield, antiradical activity (AAR) and total phenolic content (TPC). UAE water:ethanol extracts were found to be rich in phenolic compounds (up to 438984 ± 4034 ppm GAE in dry extract) with high AAR (0.36 ± 0.01 to 0.91 ± 0.02 mg/mL) and therefore were analysed using HPLC-DAD-ESI-MS/MS and DMACA assay. The profile of anthocyanins, flavonols and flavan-3-ols were significantly affected (p < 0.05) by the drying procedure. Air dried grape pomace extracts exhibited the highest total flavan-3-ol (43469 ± 1210 ppm CE), total anthocyanin (34188 ± 362 ppm Mv-3-glc eq.) and total flavonol (4484 ± 108 ppm QE) content.