Natural deep eutectic solvent extraction optimization of alkaloids from Mitragyna speciosa: A methodological evaluation

Mitragyna speciosa (kratom) is a psychoactive plant native to Southeastern Asia, belonging to the Rubiaceae family. Traditionally, its fresh leaves have been consumed in the region for centuries due to their therapeutic properties, including pain relief. The leaves contain a variety of phytochemicals with the alkaloids being the most biologically significant constituents. In the present study - the first investigation exploring sustainable extraction methods for kratom - 47 Natural Deep Eutectic Solvent (NaDES) systems were screened. The most effective system demonstrated significantly higher extraction efficiency compared to commonly used organic solvents. The food-grade system, lactic acid : glucose was subsequently selected for optimization using a one-factor-at-a-time approach, and the optimal conditions were a molar ratio of 4:1 and a water content of 20%. Further optimization using a Box-Behnken design and response surface methodology, identified the optimal extraction conditions as a solid to liquid ratio of 30 mg/mL, a temperature of 70 °C and an ultrasound treatment time of 12 min. Finally, three recovery methods were evaluated: solid phase extraction (including strong cation exchange and reversed-phase types), macroporous resins (six types) and acid-base extraction. The highest recovery yields were obtained with strong cation exchange solid phase extraction (95%) followed by the macroporous resins XAD 18 and XAD 1600N (85%).