Objectives/ Hypothesis: Fruits and vegetables are able to scavenge free radicals due to the presence of nutrients, secondary metabolites, and phenolic compounds. These antioxidants help to prevent different chronic diseases. This study aimed to determine the antioxidant capacity and total phenolic content (TPC) of the water-soluble extracts from edible portions of selected seasonal vegetables used in Bangladesh such as Brinjal, Indian Spinach, Kangkong, Okra and Stem Amaranth.
Methods: Dry powder samples were extracted twice with distilled water at a ratio of 1:20 for 2 h at 60 ºC, centrifuged at 5600 x g for 30 min and the pooled supernatants were freeze-dried to obtain polyphenol extracts. Extracts were analysed for TPC, 2,2-diphenyl-1-1 picrylhydrazyl radical (DPPH) scavenging activity, Ferric Reducing Antioxidant Activity (FRAP) and Metal Ion Chelation Activity (MIC). Result: Amaranth extract exhibited the highest TPC at 206.36 mg GAE/g. The DPPH scavenging activity of all extracts increased with increasing concentration with pro-oxidant effect observed beyond 0.50 mg/ml. Nearly all the samples had more than 50% DPPH activity at 0.5 mg/ml. The highest FRAP activities were observed for kangkong (10.98 mM Fe2+ reduced), Brinjal (8.442 mM Fe2+ reduced) and Okra (9.46 mM Fe2+ reduced) at 1 mg/ml concentration. Finally, the highest MIC activities were also recorded at 1 mg/ml concentration for Indian spinach (46.27%), Kangkong (31.6%) and Okra (26.36%).
Conclusions: Stem amaranth exhibited the highest antioxidant properties and TPC. These results show that the investigated leafy vegetables have the potential to be used as sources of antioxidant functional food ingredients.