Subcritical Water and Sulfured Water Extraction of Anthocyanins and Other Phenolics from Dried Red Grape Skin

ABSTRACT: Water, an inexpensive and environmentally friendly solvent is an ideal solvent for industrial extraction of phenolics, but its use is limited due to poor extraction efficiency at low temperatures. In this study, subcritical water (SW) and subcritical sulfured water (SSW) (containing 1400 μg/mL sodium metabisulfite) extractions of grape skin phenolics were conducted over the temperature range of 100 to 160°C in 10°C increments for a short time (40 s), and compared with conventional hot water or aqueous 60% (v/v) methanol extractions (50°C, 1 h). The composition and contents of anthocyanins, flavonols, hydroxycinnamates, phenolic acids, and antioxidant capacities (Oxygen Radical Absorbing Capacity ORAC]) in the extracts were determined. Increasing SW extraction temperature from 100 to 160°C resulted in a linear increase in ORAC values, but extraction temperatures > 110°C resulted in decreased contents of individual and total anthocyanins. Subcritical sulfured water extracts had higher levels of total anthocyanins and total phenolics than SW extracts. The SW and SSW extracts had comparable or higher levels of anthocyanins and ORAC values than extracts obtained using conventional hot water or 60% methanol. Subcritical water at 100 to 110°C appears to be an excellent alternative to organic solvents to extract anthocyanins and other phenolics from dried red grape skin and possibly other grape processing byproducts.