Antioxidant properties of phenolic compounds in macadamia nuts

Abstract

Abstract Phenolic compounds in macadamia nuts and shells were identified, and their antioxidant activities were evaluated in refined macadamia nut oil. Thin‐layer chromatography of oil extracted from macadamia nut kernels and shells indicated the possible presence of catechol, phrogallol, and 3,4,5‐trihydroxy phenolic compounds. Four phenolic compounds were tentatively identified as 2,6‐dihydroxybenzoic acid, 2′‐hydroxy‐4′‐methoxyacetophenone, 3′,5′‐dimethoxy‐4′‐hydroxyacetophenone, and 3,5‐dimethoxy‐4‐hydroxycinnamic acid. Adding 0.01% of 2′‐hydroxy‐4′‐methoxyacetophenone, 3′,5′‐dimethoxy‐4′‐hydroxyacetophenone, or 3,5‐dimethoxy‐4‐hydroxycinnamic acid to the oil significantly increased the Rancimat induction time against the control ( P <0.0001). At this concentration, 3′,5′‐dimethoxy‐4′‐hydroxyacetophenone was the most effective compound added. Although induction times of oils with 0.01%, 2,6‐dihydroxybenzoic acid were not significantly different from the control, at 0.1% there was a significant difference from the control ( P <0.0001). The activity was the same as that of 2′‐hydroxy‐4′‐methoxyacetophenone at 0.1%.