Effect of ethanol concentration, extraction time and extraction temperature on the recovery of phenolic compounds and antioxidant capacity of Orthosiphon stamineus extracts

Optimization of phenolic extraction from Orthosiphon stamineus was carried out in present study by investigating the effects of ethanol concentration (0-100%, v/v), extraction time (60-300 min) and extraction temperature (25-65oC) on the phenolic recovery using single factor experiment. Total phenolic content (TPC), total flavonoid content (TFC) and condensed tannins content (CTC) were used for determination of phenolic compounds while 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical-scavenging capacity and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging capacity were used for evaluating the antioxidant capacities of crude extract. Experimental results showed that all extraction parameters had significant (p<0.05) effect on phenolic contents (TPC, TFC and ABTS) and antioxidant capacities (ABTS and DPPH) of crude extract. The optimized conditions for phenolic extraction were 40% ethanol for 120 min at 65oC with values of 2003.4 mg GAE/100 g DW for TPC, 1611.9 mg CE/100 g DW for TFC, 202.4 mg CE/100 g DW for CTC, 765.4 μmol TEAC/100 g DW for ABTS and 2180.9 μmol TEAC/100 g DW for DPPH. DPPH was found to be positively significantly correlated with TPC but negatively significantly correlated with CTC under the influence of ethanol concentration. As a function of extraction temperature, all antioxidant compounds assays (TPC, TFC and CTC) were negatively correlated with antioxidant capacities (ABTS and DPPH).