Antioxidant and antibacterial activities of agarwood (Aquilaria malaccensis Lamk.) leaves

Several factors involve in the synthesis of secondary metabolites in plants, including leaves maturity. The objectives of this study were to compare the antioxidant and antibacterial activities of agarwood Aquilaria malaccensis Lamk. leaves at different stages of maturity as well as to identify the group of compounds responsible to the corresponding activities. Young and old leaves of agarwood were used. Leaves were powdery dried and extracted using three different polarity solvents including chloroform, methanol and water using Soxhlet apparatus. The potential extract was fractionated using Vacuum Liquid Chromatography (VLC). Antioxidant activity was analysed using 2,2-diphenyl-1-picrylhydrazyl (DPPH) while antibacterial activity was evaluated using paper disc diffusion assay. Thin Layer Chromatography (TLC) followed by spraying with specific reagents was applied to identify groups of bioactive compounds in the potential fraction. The results showed that the methanol extract of the old leaves was the most potential extract with an IC50 value of 19.62 ± 1.49 µg/ml and the combined fraction of 1:3 chloroform: methanol and 100% methanol showed the highest antioxidant activity with IC50 17.39 ± 1.43 µg/ml. The chloroform extract of old leaves showed the highest antibacterial activity on S. aureus and E. coli with a diameter of inhibition zone of 10.83 mm and 9.92 mm respectively at concentration extract of 300 mg/ml. While the most potential fraction as antibacterial on S. aureus and E. coli was chloroform fraction that showed 3 times higher activity than the crude extract. The fraction with highest antioxidant activity contained phenolic and flavonoid, while the potential antibacterial fraction contained alkaloid and terpenoid. Old agarwood of A. malaccensis leaves showed higher potency as an antioxidant and antibacterial than the young leaves.