Evaluation of antioxidant properties of methanol and aqueous extract of rhodomyrtus tomentosa (Aiton) hassk. leaves / Azizah Munirah Ab Keram @ Ab Karem

Natural antioxidants are all those essentials elements that have the potential of stabilizing and eliminating free radicals from the body. Rhodomyrtus tomentosa (Aiton) Hassk. is a flowering plant mainly found in Southeast Asian country which includes Thailand and Malaysia and is said to often consumed as medicinal nourishment. In this study, the phytochemical constituent properties and antioxidant capacity of R. tomentosa leaves were assessed spectrophotometrically by two different extraction solvent, absolute methanol (alcohol) and distilled water (aqueous). The phytochemical constituent was determined with Total Phenolic Content (TPC) assay and Total Flavonoid Content (TFC) assay whereas the antioxidant capacity was determined by DPPH Radical Scavenging Activity assay and Ferric Reducing Antioxidant Power (FRAP) assay. In TPC assay, absolute methanol leaves extract of R. tomentosa gave significant result compared to aqueous leaves extract of R. tomentosa in consistent to gallic acid equivalents which are 448.54 ± 0.43 mg GAE/g and 263.93 ± 0.33 mg GAE/g of extracts, respectively, with a p-value less than 0.05. Whereas in TFC assay, the same trend occurred when absolute methanol leaves extract of R. tomentosa gave a significant result compared to aqueous leaves extract of R. tomentosa in consistent to quercetin equivalents which are 6495.23 ± 64.756 mg QE/g and 777.01 ± 4.053 mg QE/g of extracts, respectively (p < 0.05). In DPPH radical scavenging activity, the IC 50 were found to be in the order of ascorbic acid (16.67 ± 0.199 µg/mL) > absolute methanol leaves extract of R. tomentosa (21.96 ± 0.033 µg/mL) > aqueous leaves extract of R. toementosa (32.00 ± 0.014 µg/mL), and these values are significant between each other (p < 0.05). Lastly, in FRAP assay, the absolute methanol leaves extract of R. tomentosa showed a significantly (p < 0.05) higher value of FRAP (expressed as gallic acid equivalents) as compared to aqueous leaves extract of R. tomentosa which is 702.74 ± 7.361 mg GAE/g and 137.29 ± 2.252 mg GAE/g, respectively. Data are expressed in mean (SEM) (n = 3), with p value less than 0.05 are considered significant. In conclusion, absolute methanol is an ideal solvent for extraction to further assess phytochemical constituent and antioxidant capacity of R. tomentosa in the future. Further in vivo studies are needed explicitly aiming at the potential antioxidant ability on the leaves extract of R. tomentosa.