Optimisation of microwave-assisted extraction parameters for total phenolic content from Eucalyptus robusta using response surface methodology

Eucalyptus robusta (E. robusta) has been shown to possess many pharmacological properties in vitro in addition to its significance in traditional medicine. This study utilised microwave-assisted extraction (MAE) to yield optimal total phenolic content (TPC) and total antioxidants from E. robusta. Response surface methodology (RSM) with a three- level-three-factor Box–Behnken design evaluated the effect of parameters associated with MAE such as irradiation time, power and sample-to-solvent ratio on the yields of TPC and total antioxidants using Folin-Ciocalteu and ABTS assays respectively. The accuracy and reliability of RSM as a tool for predicting the yield of TPC using MAE was validated (model, p = 0.0014; R2 = 0.97; lack of fit, p = 0.052). TPC yield was highly affected by the sample-to-solvent ratio followed by power and irradiation time. An experimental yield of 58.40 ± 1.03 mg GAE/g was obtained for TPC and 64.6% of the maximum ABTS value was liberated under the optimal conditions- 3 min irradiation time, 50% (600 W) microwave power, 2 (g/100mL) sample-to-solvent ratio. It was concluded that MAE is a reliable and efficient method for extracting high yields of TPC from E. robusta with significant potential to be up-scaled for nutraceutical or pharmaceutical applications.