Evening Primrose Meal: A Source of Natural Antioxidants and Scavenger of Hydrogen Peroxide and Oxygen-Derived Free Radicals

Abstract

Evening primrose meal (EPM: 1% and 2%, w/w) reduced (p ≤ 0.05) the formation of 2-thiobarbituric acid-reactive substances (TBARS), hexanal, and total volatiles in cooked comminuted pork by 43.6−72.6%. Phenolic compounds in the EPM were extracted under optimum conditions (with 56% acetone at 71 °C for 47 min) predicted by a multivariate analysis. The resulting evening primrose crude extract (EPCE) inhibited the bleaching of β-carotene in a model system. After 2 h of assay, the system containing 200 ppm EPCE [as (+)catechin equivalents] retained 86% of the initial β-carotene whereas the control retained only 11%. Inhibition of the formation of TBARS, hexanal, and total volatiles in the cooked comminuted pork containing 200 ppm EPCE [as (+)catechin equivalents] ranged from 67.3% to 97.5%. The EPCE inhibited the formation of conjugated dienes, hexanal, and total volatiles in stripped-bulk corn oil (18.5−63.6% inhibition) and stripped-corn oil-in-water emulsion systems (31.7−65.6% inhibition). Hydrogen peroxide (H₂O₂), hydroxyl radical (^•OH), and superoxide radical (O₂^•-) scavenging properties of the EPCE were comparable to those observed for authentic (+)catechin. At 200 ppm of the EPCE [as (+)catechin equivalents], a 100% quenching of ^•OH and O₂^•- was evident. The EPCE scavenged 44−91% of H₂O₂ in the assay medium after 10 min as compared to 7% reduction in the control. Keywords: Antioxidants; free radicals; evening primrose; lipid oxidation; reactive-oxygen species, ROS; electron paramagnetic resonance, EPR