Evaluation of synergistic interactions of antioxidants from plant foods by a new method using soybean lipoxygenase

A proper evaluation of synergism among antioxidants remains so far rather difficult to obtain. We recently reported that a new method for antioxidant activity measurement, based on the secondary reaction of soybean lipoxygenase (LOX)-1 isoenzyme with 4-nitroso-N,N-dimethylaniline (RNO), so-called LOX/RNO method, may assess very well the synergism among antioxidants from durum wheat whole semolina. To evaluate whether this behaviour is generalizable to different food matrices, herein, antioxidants from other very different sources were analysed. For this purpose, antioxidant activity of food-grade preparations enriched in catechins, quercetin, resveratrol, tyrosol/hydroxytyrosol and lycopene was evaluated by the LOX/RNO method in comparison with the Trolox equivalent antioxidant ca pacity (TEAC) assay. The antioxidant activity values obtained by LOX/RNO method were 2–90-times higher than those obtained by the TEAC protocol, depending on the tested antioxidant. Synergism was evaluated by comparing antioxidant activity of the mixture of compounds (AAmix) with the sum of antioxidant activity values of individual compounds (AAsum). The LOX/RNO method revealed a strong synergism, being AAmix 5.69 ± 0.31 times higher than AAsum (statistically significant, p < 0.001), while the TEAC method showed a synergistic increase of only 0.31 ± 0.04 (statistically significant, p < 0.01). These findings suggest that the LOX/RNO method is able to assess very well the synergism in various food samples.