Effect of Drying Methods on the Phenolic Compounds and Antioxidant Activity of Leaf of Agarwood (Aquilaria malaccensis Lam.)

This study is a preliminary analysis of the effect of various drying techniques on the phenolic components and antioxidant capability for developing protocols to produce herbal products from Aquilaria malaccensis. Aquilaria leaf samples (ALS) were subjected to different drying methods such as air-dry (AD), oven-dry (OD), sun-dry (SD), drying with food dehydrator (DD), and a combination of air-dry and use of dehydrator (CAD). After drying and grinding, samples were infused with hot water. Different parameters such as water extract, total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activities were evaluated. Results revealed that there was no significant difference in the water extract of ALS among different methods. High TPC concentrations were recorded at SD, OD, and DD. The highest TFC concentration was observed in CAD and was significantly different among the drying treatments. Further, using 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, the dehydrated-ALS possessed the highest antioxidant capacity of 524.33 ± 0.04 μmol TEAC/g among the treated samples. Meanwhile, based on the cupric reducing antioxidant capacity (CUPRAC) assay, the highest antioxidant activity among the treatments was sundried-ALS with a value of 391.70 ± 0.037 μmol TEAC/g sample. Based on these findings, the drying methods – particularly utilizing a dehydrator, sun- drying, or a combination of air-drying and using a dehydrator – all preserve the phenolics and antioxidant properties of A. malaccensis. Overall, the drying process significantly influenced the chemical characteristics and antioxidant activity of A. malaccensis tea.