Antioxidant Capacity of Oat (Avena sativa L.) Extracts. 1. Inhibition of Low-Density Lipoprotein Oxidation and Oxygen Radical Absorbance Capacity

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Abstract
Milled oat groat pearlings, trichomes, flour, and bran were extracted with methanol and the fractions tested in vitro for antioxidant capacity against low-density lipoprotein (LDL) oxidation and R-phycoerythrin protein oxidation in the oxygen radical absorbance capacity (ORAC) assay. The oxidative reactions were generated by 2,2‘-azobis(2-amidinopropane) HCl (AAPH) or Cu2+ in the LDL assay and by AAPH or Cu2+ + H2O2 in the ORAC assay and calibrated against a Trolox standard to calculate Trolox equivalents (1 Trolox equivalent = 1 TE = activity of 1 μmol of Trolox). The antioxidant capacity of the oat fractions was generally consistent with a potency rank of pearlings (2.89−8.58 TE/g) > flour (1.00−3.54 TE/g) > trichome (1.74 TE/g) = bran (1.02−1.62 TE/g) in both LDL and ORAC assays regardless of the free radical generator employed. A portion of the oat antioxidant constituents may be heat labile as the greatest activity was found among non-steam-treated pearlings. The contribution of oat tocols from the fractions accounted for 2+-initiated oxidation of LDL stimulated peroxide formation with low oat concentrations but completely inhibited oxidation with higher doses. Thus, oats possess antioxidant capacity most of which is likely derived from polar phenolic compounds in the aleurone. Keywords: Avena sativa; oat; antioxidant capacity; phenolics; radical scavengers; oxygen radical absorbance capacity (ORAC); low-density lipoprotein (LDL) oxidation; aleurone