Alkaloid Biosynthesis in Medicinal Crop Kratom (Mitragyna speciosa) Varies with Postharvest, Genetic, and Seasonal Factors

Mengzi Zhang¹Annabella Lyndon²Siva Rama Raju Kanumuri³Abhisheak Sharma³Brian J Pearson⁴Christopher R Mccurdy⁵Jianjun Chen^1*

• ¹Environmental Horticulture Department, University of Florida Mid-Florida Research and Education Center, Apopka, United States
• ²University of Florida Mid-Florida Research and Education Center, Apopka, United States
• ³Department of Pharmaceutics, University of Florida College of Pharmacy, Gainesville, United States
• ⁴Mid-Columbia Agricultural Research and Extension Center, College of Agricultural Sciences, Oregon State University, Corvallis, United States
• ⁵Department of Medicinal Chemistry, University of Florida College of Pharmacy, Gainesville, United States

Kratom (Mitragyna speciosa) is a medicinally valuable ethnobotanical tree native to Southeast Asia, traditionally used to combat fatigue and enhance productivity. In recent years, it has gained attention in North America and Europe for its potential therapeutic applications, particularly in pain management and opioid withdrawal, positioning it as a promising candidate for drug development. Postharvest processing is a critical stage in the kratom farm-to-pharmacy pipeline, where chemical transformations of bioactive compounds may occur. This study examined the effects of withering duration, drying temperature, cultivar, and season on kratom alkaloid composition. In Study I, leaves from cultivar Hawaii underwent four withering durations (0, 12, 24, and 72 hours) followed by drying at five temperatures (-40, 25, 40, 60, and 80 °C). In Study II, cultivar MR-Malaysian leaves were tested with two withering durations (0 and 12 hours) and two drying temperatures (25 and 60 °C). Both studies were repeated in two separate seasons. Withering overall increased mitragynine concentration by 14-65% w/w in 'Hawaii' and 3-8% in 'MR-Malaysian' extracts. A 12-hour withering enhanced the concentration of speciogynine and paynantheine by 37-48% and 35-67% in 'Hawaii' when leaves were dried below 40 ℃. Low drying temperature generally preserves mitragynine, speciogynine, and paynantheine in kratom. The average 7-hydroxymitragynine ranged from 0.02-0.04% in extracts, detected only in specific seasons varying with cultivars, suggesting potential genetic differences in response to environmental factors. These findings highlight the importance of postharvest handling, genotype selection, and seasonal timing in optimizing kratom's alkaloid profile for medicinal use.