Antioxidant capacity of oat (Avena sativa L.) extracts. 1. Inhibition of low-density lipoprotein oxidation and oxygen radical absorbance capacity

Milled oat great 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 oxidat ion in the oxygen radical absorbance capacity (ORAC) assay. The oxidative r eactions were generated by 2,2'-azobis(2-amidinopropane) HCl (AAPK) or Cu2 in the LDL assay and by AAPH or Cu2+ + H2O2 in the ORAC assay and calibrat ed against a Trolox standard to calculate Trolox equivalents (1 Trolox equi valent = 1 TE = activity of 1 mu mol of Trolox). The antioxidant capacity o f the oat fractions was generally consistent with a potency rank of pearlin gs (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 h eat labile as the greatest activity was found among non-steam-treated pearl ings. The contribution of oat tocols from the fractions accounted for <5% o f the measured antioxidant capacity. AAPH-initiated oxidation of LDL was in hibited by the oat fractions in a dose-dependent manner, although complete suppression was not achieved with the highest doses tested. In contrast, Cu 2+-initiated oxidation of LDL stimulated peroxide formation with low oat co ncentrations but completely inhibited oxidation with higher doses. Thus, oa ts possess antioxidant capacity most of which is likely derived from polar phenolic compounds in the aleurone.