Commercial Dietary Ingredients from Vitis vinifera L. Leaves and Grape Skins:  Antioxidant and Chemical Characterization

This paper reports an attempt to functionally and chemically characterize commercial ingredients from Vitis vinifera L. grape skins, grape pomace, and leaves, which are used in the formulation of dietary antioxidant supplements. The antioxidant capacity of these ingredients was assessed for the first time by the oxygen radical absorbance capacity (ORAC) methodology. Ingredients from grape skins and pomace (n = 17) showed ORAC values from 1.38 to 21.4 μmol Trolox equivalents/mg whereas ingredients from leaves (n = 4) showed ORAC values from 1.52 to 2.55 μmol Trolox equivalents/mg. The high-performance liquid chromatography−diode array detection/electrospray ionization−mass sprectrometry analysis of anthocyanins and flavonols revealed the authenticity of the ingredients as derived from V. vinifera L. and confirmed large differences in their phenolic content and distribution. A progressive decline in both antioxidant capacity and total anthocyanin content of a grape skin ingredient (43 and 40% decrease, respectively) was observed over a 60 day storage period (45 °C and 75% relative humidity), demonstrating its poor stability under these conditions. Keywords: ORAC; anthocyanins; flavonols; commercial ingredients; Vitis vinifera L. grape skins; grape pomace; leaves