Effects of Solvent and Temperature on Pressurized Liquid Extraction of Anthocyanins and Total Phenolics from Dried Red Grape Skin

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Abstract
Pressurized liquid extraction (PLE) was used to extract anthocyanins from the freeze-dried skin of a highly pigmented red wine grape with six solvents at 50 °C, 10.1 MPa, and 3 × 5 min extraction cycles. Temperature (from 20 to 140 °C in 20 °C increments) effects on anthocyanin recovery by acidified water and acidified 60% methanol were also studied. Acidified methanol extracted the highest levels of total monoglucosides and total anthocyanins, whereas the solvent mixture (40:40:20:0.1 methanol/acetone/water HCl) extracted the highest levels of total phenolics and total acylated anthocyanins. Acidified water extracts obtained by PLE at 80−100 °C had the highest levels of total monoglucosides, total acylated anthocyanins, total anthocyanins, total phenolics, and ORAC values. Acidified methanol extracts obtained by PLE at 60 °C had the highest levels of total monoglucosides and total anthocyanins, whereas extracts obtained at 120 °C had the highest levels of total phenolics. High-temperature PLE (80−100 °C) using acidified water, an environmentally friendly solvent, was as effective as acidified 60% methanol in extracting anthocyanins from grape skins. Keywords: Red grape; pressurized liquid extraction; anthocyanins; phenolics; antioxidant capacity; ORAC