Determination of synergistic effects of polymethoxylated flavone extracts of Jinchen orange peels (<Emphasis Type="Italic">Citrus Sinensis</Emphasis> Osberk) with amino acids and organic acids using chemiluminescence

Antioxidant capacity of polymethoxylated flavones (PMFs) extracts of Jinchen orange peels (Citrus sinensis Osberk) was evaluated by using a chemiluminescence (CL) method in vitro. PMFs were isolated using a procedure that produced a consistent mixture of PMFs both in identity and in proportion. The mixture mainly consisted of nobiletin (55.9%), sinensetin (15.2%), heptamethoxyflavone (13.2%), and tangeretin (8.1%). The antioxidative effects of PMFs and the main individual flavones in PMFs as well as synergistic effects of PMFs with organic acids (citric acid, oxalic acid, and malic acid) and amino acids (alanine, lysine, serine, and threonine) on superoxide anion were determined by the pyrogallol–luminol system. The results showed that the inhibition by PMFs on superoxide radical was stronger than that of the individual flavones. Mixtures of citric acid and lysine with PMFs had higher synergistic effects than any other tested mixtures, and the optimum concentrations were exhibited by combinations of 7 μg/mL PMFs + 120 μg/mL citric acid (1.2, p < 0.05) and 7 μg/mL PMFs + 42 μg/mL lysine (1.1, p < 0.05). For the other amino acids and organic acids, the values of the measured inhibition effect (% MIE) of the mixtures with PMFs were not significantly different from their expected inhibition effect (% EIE), which did not show synergism.