Antioxidant activity, total phenolic and vitamin C contents of selected fresh and dried fruit peels from Sabah

Five tropical fruits (bambangan, tarap, salak, dragon fruit, pomelo (flavedo and albedo) from Sabah were selected in this study to determine their antioxidant activity, total phenolic and vitamin C contents in the form of fresh and • dried peels. All samples were obtained from local market in Kota Kinabalu, Sabah. Samples were extracted using methanol solution for measuring antioxidant activity by FRAP (Ferric Reducing Antioxidant Power), DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical scavenging and I²-carotene bleaching assays and total phenolic content by Folin-Ciocalteu method. Vitamin C content of samples was measured by UV-vis spectrophotometry of 2,6-dichlorophenolindophenol (DCIP). Fresh bambangan and dried tarap peel displayed the highest free radical scavenging (EC50 values of 0.18 ± 0.16mg/ml and 0.04 ± 0.00mg/ml, respectively), ferric reducing (15.23 ± 0.62mg Trolox /g extract and 11.00 ± 3.81 mg Trolox /g extract, respectively) and linoleic acid scavenging activities (EC50 values of 1.56 ± 0.02mg/ml and 0.80 ± 0.01mg/ml, respectively). Both fresh and dried flavedo of pomelo contained the highest vitam in C content. The antioxidant activity of fruit peels, except I²-carotel1e bleaching, were significantly (p < 0.05) correlated with the total phenolic content. However, those assays were not correlated with vitamin C content. This study indicated that phenolics were the major contributor for antioxidant activity while vitamin C was only a minor contributor. Overall, fresh bambangan and dried tarap peels had the highest potential as natural source of antioxidant among the selected samples.