Subcritical water extraction of essential oil from Aquilaria malaccensis leaves

Hydro-distillation (HD) has been widely used in the extraction of essential oil, yet it is a low efficient method that consumes time and energy. In this work, A. malaccensis' oils have been extracted using subcritical water extraction (SCWE) from its leaves to determine the optimum parameters using analysis of variance. Quadratic model was deduced to be most suitable to analyze SCWE parameters. Regression analysis indicated that interaction of temperature and reaction time parameters exerted great influence on the yield. Kinetic modeling was conducted to study SCWE's mechanism, and second-order model was concluded to be the best model for SCWE. Optimum extraction conditions of essential oil were 156 degrees C, 0.2 w/w, 25 min. Gas chromatography/mass spectroscopy characterization was conducted and results indicated that the quality of A. malaccensis' leaves oils extracted by SCWE significantly improved compared to previous studies. Additionally, the essential oils extracted by SCWE contained several value-added compounds useful in medicine such as furfural and guaiacol. Fourier transform infrared, scanning electron microscopy, and Brunauer-Emmett-Teller and Barrett-Joyner-Halenda on the leaves samples provided further evidence for better performance of SCWE, as the sample's pores, cell walls, cellulose, and hemicellulose were more damaged. The result showed that compared to extraction yield of HD method, that of SCWE was 2.5 times higher, while the requiring time was 8.4 times shorter. Therefore, it was concluded that SCWE is a better extraction method in terms of time, efficiency, yield, and quality.