Parametric optimization of microwave reflux extraction of spice oleoresin from white pepper (Piper nigrum)

Background: White Piper nigrum is an important commodity crop containing a number of essential bioactive components with nutritional and medicinal properties when sufficiently extracted. Microwave refluxation is therefore a novel technique employed in the extraction of bioactive components from natural products of plant origin. This method doubled as classical and traditional solvent extraction techniques with reduced extraction time, higher selectivity, low solvent consumption, and higher extraction rate. Methods: The Taguchi L-9-orthogonal design was employed to determine a combination of extraction factors that jointly optimized the extraction yield. The use of this para metric design was due to its ability to mitigate inherent noise factor with minimal experimental trials. Results: The optimal extraction condition was attained at 90 min of irradiation time, 300 W of microwave power, 0.105 mm of particle size, and 10 ml/g of molar ratio. Under this condition, the corresponding optimum extraction yield of 4.278 (v/w)% was obtained. Moreover, the percentage contribution of each extraction factor on the response settings resulted in the decreasing order: irradiation time > molar ratio > power level > particle size. Phytochemical screening was condcuted on the oleoresin extracts and a total number of 26 bioactive compounds were identified. Also, the Fourier Transform Infrared Analysis (FTIR) and the Scanning Eectron Microscopy (SEM) confirmed the presence of seven presence of seven functional groups with an observable structural transformation. Conclusions: The result of optimum design, phytochemical screening, and structural characterization therefore provided a better understanding on the potential of microwave refluxation in extracting spice oleoresin from white Piper nigrum.