Antioxidant potential of aroma compounds obtained by limonene biotransformation of orange essential oil

The antioxidant activities of a limonene biotransformation extract and of some standard monoterpenes present in the extract were assessed using four antioxidant assays: total antioxidant capacity, based on the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging assay, lipid peroxidation by the thiobarbituric acid (TBA) assay, superoxide anion release by cultured leukemic cells and glutathione S-transferase (GSTs) activity. The limonene biotransformation extract had free radical-scavenging activity (EC50 = 2.09%, v/v) and inhibited lipid peroxidation (IC50 = 0.13%, v/v). The extract, perillyl alcohol and α-terpineol inhibited lipid peroxidation by ∼80% at a concentration of 0.02% (v/v). Perillyl alcohol and α-terpineol also reduced the release of superoxide anions by cultured leukemic cells, by 3- and 10-fold, respectively, at concentrations of <0.02% (v/v). The biotransformation extract inhibited the conversion of nitrophenyl acetate to p-nitrophenol in the glutathione assay by ∼50%. These results indicate that, in addition to monoterpenes, other non-volatile compounds may contribute to the antioxidant activity of the biotransformation extract.