Comparison of Five Antioxidant Assays for Estimating Antioxidant Capacity from Three Solanum SP. Extracts

Abstract

Objectives: The aims of this research were to determine antioxidant capacity of various extracts from black nightshade, turkey berry, and round green eggplant using five antioxidant assays which were ferric reducing antioxidant power (FRAP), cupric reducing antioxidant capacity (CUPRAC), H2O2 scavenging, phosphomolybdenum assay, and beta-carotene bleaching (BCB), correlation of total phenolic, flavonoid, and carotenoid content with their inhibitory concentration 50% (IC50) and exhibitory concentration 50% (EC50) of five antioxidant assay and correlation between five antioxidant assays. Methods: Extraction was conducted by reflux using gradient polarity solvents. The extracts were evaporated using rotary evaporator. The antioxidant capacity study, determination of phenolic, flavonoid, and carotenoid content were performed by ultraviolet-visible spectophotometry, while its correlation with IC50 and EC50 of five methods were analyzed by Pearson’s method. Results: Ethanolic and ethyl acetate fruit extracts of turkey berry denoted the highest antioxidant capacity using FRAP (EC50: 41.32 µg/ml), H2O2 scavenging assay (IC50: 1.01 µg/ml), and CUPRAC (EC50: 117.56 µg/ml). While ethyl acetate fruit extract of round green eggplant gave the highest phosphomolybdenum capacity (EC50: 375.47 µg/ml), and ethyl acetate fruit extract of black nightshade showed the highest BCB capacity (EC50: 158.66 µg/ml). Phenolic content of all fruit extracts had a tendency to correlate with FRAP and H2O2 scavenging antioxidant capacity, meanwhile flavonoid and carotenoid content had a tendency to correlate with CUPRAC, phosphomolybdenum, and BCB antioxidant capacity. Conclusions: Phenolic compounds were a major contributor in antioxidant capacity of black nightshade, turkey berry, and round green eggplant extracts using FRAP and H2O2 scavenging, meanwhile flavonoid and carotenoid compounds were a major contributor in antioxidant capacity using CUPRAC, phosphomolybdenum and BCB assays. FRAP assay had linear correlation with H2O2 scavenging, meanwhile CUPRAC had linear correlation with phosphomolybdenum and BCB.