Total phenolic, flavonoid content, and antioxidant activity of Gluta torquata extracts

Abstract

The main objective of this study was to investigate and compare the total phenolic, flavonoid content and antioxidant activity of the methanolic extract of the leaf, bark and wood of Gluta torquata. The chosen species is an Anacardiaceae species, which was collected from Gunung Jerai, Kedah, Malaysia. It is a toxic, hardwood plant where its sap can cause serious skin irritation. This work was prompted because of little reports on the phytochemical composition of this species. Air dried wood, leaf and bark of Gluta torquata were grounded and extracted under reflux using methanol for 6 h. The methanolic extracts were then subjected to evaluation of total phenolic and flavonoid content. The total phenolic content was measured at 760 nm via UV-Vis spectrophotometry using Folin-Ciocalteu reagent, while total flavanoid content was determined by aluminum chloride colorimetric assay at 510 nm via UV-Vis spectrophotometry. The antioxidant activity of the extracts were done using DPPH (1,1-diphenyl-2-picryl-hydrazyl) free radical scavenging method of Brand-William. The absorbance of solutions were measured at 515 nm via UV-Vis spectrophotometry after 30 min incubation in the dark. Quercetin was used as the standard. The absorbance of different concentrations were recorded and EC50 was calculated for each extract. Among the 3 extracts, the wood extract of Gluta torquata had the highest total phenolic and total flavonoid content which was 81.46 µg gallic acid equivalent (GAE) per 1 mg extract and 395.79 µg catechin equivalent (CE) per 1mg extract, respectively. The results also showed that wood extract had the highest antioxidant activity with the lowest EC50 of 28.14 µg/mL. The standard quercetin yielded EC50 of 13.36 µg/mL. This preliminary study had shown that there was a high amount of phenolic content in the wood extract of Gluta torquata that can lead for further analysis to study the details of the phenolic content.