The Evaluation of Antioxidant Interactions among 4 Common Vegetables using Isobolographic Analysis

Isobolographic analysis was used to assess the antioxidant interactions (synergism, addition, and antagonism) of 4 common vegetables (tomato T], carrot C], eggplant E], and purple potato P]). The lipophilic (L) extracts of T and C (main carotenoids), the hydrophilic (H) extracts of E and P (main phenolics) were mixed by the certain ratios (1:9, 3:7, 1:1, 7:3, 9:1, w/w) and their antioxidant activities were investigated by 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) and 2,2’‐Azinobis‐(3‐ethylbenzthiazoline‐6‐sulphonate) (ABTS) radical scavenging assays, respectively. Most of the binary mixtures (LC‐HE, LC‐HP, HE‐HP, LT‐HE, and LT‐HP combinations) showed the synergistic antioxidant effects. In DPPH assay, the greatest antioxidant activity of vegetable combinations was 1:9 LT‐HP (EC₅₀: 2.45 ± 0.13 mg/mL), followed by 9:1 HE‐HP (EC₅₀: 3.62 ± 0.12 mg/mL) and 1:9 LC‐HE (EC₅₀: 3.74 ± 0.47 mg/mL). In ABTS assay, the greatest antioxidant activity of vegetable combinations was 9:1 HE‐HP (EC₅₀: 4.20 ± 0.10 mg/mL), followed by 7:3 HE‐HP (EC₅₀: 4.41 ± 0.63 mg/mL) and 1:1 HE‐HP (EC₅₀: 5.35 ± 0.85 mg/mL). Among these combinations, 1:1 LC‐HE combination showed the highest synergistic antioxidant effects in DPPH assay (synergistic rate: 87.4%), and 7:3 LC‐HE combination showed the highest synergistic antioxidant effects in ABTS assay (synergistic rate: 87.0%). The mixtures of phenolics and carotenoids with suitable ratios in vegetables effectively enhanced the synergistic antioxidant effects.