Microwave-assisted extraction as an advanced technique for optimisation of limonoid yields and antioxidant potential from Trichilia roka (Meliaceae)

Response surface methodology (RSM) was applied to predict optimum conditions for microwave-assisted extraction (MAE) of total limonoid (TL) and antioxidant potential investigation from Trichilia roka (Chiov) root bark. A central composite design methodology (CCDM) was used to minor the effect of the independent variables such as irradiation time (X1), irradiation power (X2), liquid-to-solid ratio (X3) and methanol polarity (X4) on the dependent variables namely total limonoid (TL), total polyphenol (TPP), DPPH radical scavenging activity and β-carotene antioxidant activity (AOA). The optimal combined conditions for extracting maximum TL (116 ​mg RUBE/gDW), TPP (12.5 ​g GAE/100gDW) and antioxidant activity (DPPH 90.1%; AOA 90.5%) were irradiation time 80 ​s, irradiation power 600 ​W, liquid to solid ratio 0.6/20 ​mL/g and methanol concentration 40%. All the factors significantly (p ​< ​0.01) influenced the responses, the variations from the independent variables corresponding significantly to the predicted polynomial model and the maximum values estimated at the predicted optimal condition were in good agreement with experimental value. In conclusion MAE of antioxidant compounds from Trichilia roka (Chiov) root bark is highly influenced by equipment parameters of functioning (microwave irradiation time and power) as well as the solvent (liquid to solid ratio and methanol concentration), following a second degree polynomial model