Various methods have been developed in recent years to evaluate the total antioxidant activity of food and biological samples. In this study, a new ferric iron reducing assay was applied for measuring total antioxidants. This method is based on the oxidation on the reducing the iron III to iron II. The extraction was incubated with Fecl3 and KSCN. Ferric thiocyanate complex is formed in an acid solution. This complex is measured at 474 nm. A lower absorbance indicates increased reducing power.
Grewia bicolorbelongs to Malvaceae family of the genus Grewia. G. bicolorfinds several therapeutic applications in the ethno-medicine which include in treating syphilis, fever and inflammation and as diuretic, vermifuge, laxative and antidote for common poisons. The present study aimed to evaluate the antioxidant potential, determine the IC50 value, determine total phenolic contents (TPCs) and determine total flavonoid contents (TFCs) of various solvent extracts obtained from the leaves and stem-bark of G. bicolor. Maceration and hot solvent extraction techniques were employed to obtain various solvent extracts. DPPH radical scavenging assay was employed to evaluate the antioxidant potential and determine the IC50 values. Folin-Ciocalteu colorimetric method and aluminium chloride colorimetric method were employed to estimate the TPCs and TFCs, respectively. The percentage of DPPH radical scavenged by various extracts obtained from the leaves, stem-bark and the positive control (ascorbic acid) at a concentration range of 200-3000 µg/mL was in the ranges of 6.53±0.15-74.75±0.03, 17.87±0.56-86.04±0.29 and 53.76±0.13- 83.30±0.96%, respectively. Similarly, the IC50 values of various extracts obtained from the leaves and stem-bark were determined to be in the ranges of 457.78-2425.37µg/mL and 649.29-1869.62µg/mL, respectively and the positive control exhibited an IC50 value of < 200 µg/mL. The acetone extracts from both leaves and stem-bark showed lowest IC50 values of 457.78µg/mL and 649.29µg/mL, respectively. The TPCs of various extracts from leaves and stem-bark were in the ranges of 0.850±0.02-9.728±0.09 and 0.813±0.16-12.259±0.03mg of gallic acid equivalent per gram dry weight of the extract (mg GAE/g DW), respectively. The TFCs of various extracts from leaves and stem-bark were in the ranges of 20.211±0.54-46.004±0.08 and 22.054±0.25-42.128±0.18mg of quercetin equivalent per gram dry weight of the extract (mg QE/g DW), respectively. From this study, we concluded that various extracts obtained from the leaves and stem-bark of G. bicolorshowed a moderate to significant DPPH radical scavenging potential and possessed a moderate to significant TPCs and TFCs. In general, the TFCs of these extracts were relatively higher than TPCs. Further studies on this plant are required to substantiate its therapeutic applications in the traditional medicines.
