Comparison of subcritical water and organic solvents for extracting kava lactones from kava root

Subcritical water extraction of lactones from a kava (Piper methysticum) root was compared to a Soxhlet extraction with water, to boiling in water, and to a sonication in acetone. For ground kava (250–500 μm), 2 h of subcritical water extraction were required for a complete extraction at 100°C, while at 175°C, 20 min were sufficient. For a complete extraction of the unground (shredded) kava, the time of extraction was extended to 40 min at 175°C. Boiling for 2 h and extraction with Soxhlet apparatus for 6 h, both of which employed water at atmospheric pressure, produced yields 40–60% lower than those obtained with subcritical water. With unground kava, 40 min of subcritical water extraction yielded essentially the same recoveries of lactones as 18 h of sonication with acetone, methylene chloride, or methanol.