The effect of extraction conditions on total phenolic content and free radical scavenging capacity of selected tropical fruits’ peel

The present study aimed to investigate the effects of ethanol concentration (0100%, v/v), extraction time (60-300 min), and extraction temperature (25-60°C) on total phenolic content (TPC) and free radical-scavenging capacity of rambutan (Nephelium lappaceum), mangosteen (Garcinia mangostana), and langsat (Lansium domesticum) peels using single-factor experiments. Folin-Ciocalteu’s method was used for the determination of TPC, while the antioxidant capacity was determined by 2,2’-diphenyl-1-picrylhydrazyl (DPPH) radicalscavenging assay. All the extraction conditions showed significant effect (p<0.05) on TPC and DPPH radical-scavenging capacity. The best extraction conditions determined for rambutan peel were 80% ethanol concentration for 120 min at 50°C; for mangosteen peel were 60% ethanol concentration for 60 min at 25°C; and 80% ethanol concentration for 120 min at 25°C were the best extractions for langsat peel. Extracts were then subjected to various antioxidant assays such as DPPH assay, TPC, nitric oxide scavenging activity (NO) and β-carotene bleaching (BCB) assay. Based on these optimized extraction conditions, high antioxidant capacity was obtained with EC50 value of 8.87 μg/mL (DPPH radical scavenging activity), 64.88% for NO activity, and 98.19% for BCB activity; as well as 53.94 mg GAE/g (TPC) for rambutan peel. While mangosteen peel showed a EC50 value of 19.75 μg/mL (DPPH), 54.66% (NO), 79.94% (BCB), and TPC value of 42.25 mg GAE/g; and langsat peel with EC50 value of 85.28 μg/mL (DPPH), 50.42% (NO), 23.95% (BCB) and TPC value of 22.04 mg GAE/g. With these extraction Samuagam et al. 2013 Health and the Environment Journal, 2013, Vol 4, No 2 pp 80-102 81 conditions, maximum antioxidant capacity could be obtained for future studies of all the selected fruits peel and it will be useful for nutraceutical development.