UAE, MAE, SFE-CO2 and classical methods for the extraction of Mitragyna speciosa leaves

Mitragyna speciosa, a tropical plant indigenous to Southeast Asia, is well known for its psychoactive properties. Its leaves are traditionally chewed by Thai and Malaysian farmers and manual labourers as it causes a numbing, stimulating effect. The present study aims to evaluate alkaloid yield and compn. in the leaf exts. For this purpose we have compared several non-conventional extn. techniques with classic procedures (room temp. or under heating). Dried M. speciosa leaves belonging to three batches of different origin (from Thailand, Malaysia and Indonesia) were extd. using ultrasound-assisted extn. (UAE), microwave-assisted extn. (MAE) and supercrit. carbon dioxide extn. SFE-CO2, using methanol, ethanol, water and binary mixts. The exts. were compared using an HPLC/ESI-MS anal. of mitragynine and four other related alkaloids which were present in the alkaloid fraction. The extn. technique influences both the raw product yield and the relative alkaloid content of M. speciosa leaves. Of the several methods tested, MAE in a closed vessel at 110 °C (60 W, methanol/water 1:1) gave the highest alkaloid fraction amt., while UAE with an immersion horn at 25 °C (21.4 kHz, 50 W, methanol) showed the best yield for mitragynine. This work may prove to be a useful contribution to forensic, toxicol. and pharmacognosy studies. Although the potential applications of M. speciosa alkaloids clearly need further investigation, these results may facilitate the scaling-up of their extn.