Drying and quality characteristics of Cannabis sativa L. inflorescences under constant and time-varying convective drying temperature schemes

Cannabis sativa L. is an herbaceous, dioicous, annual medicinal plant of the Cannabaceae family. Two of the most important cannabinoids with pharmaceutical properties produced are the Delta(9)-tetrahydrocannabinol (Delta(9)-THC) and the cannabidiol (CBD). The present work aims to investigate the convective drying characteristics of hemp inflorescences, evaluate the effects of constant and time-varied temperature schemes on the CBD and Delta(9)-THC concentrations and estimate the energy requirements of each drying regime. Constant temperature drying of inflorescences was performed for 40, 50 and 60 degrees C, while the rates of temperature increase evaluated for the non-isothermal drying experiments have been 1.5, 2.5 and 4 degrees C.h(-1) for the aforementioned temperature range limits (40-60 degrees C), under a constant airflow of 1 m.s(-1). Considering all experiments, the highest temperature level and temperature increase rate resulted in reduced processing time and energy consumption, while the total content of CBD and Delta(9)-THC of inflorescences ranged between 0.653-1.335% w/w and 0.036-0.062% w/w, respectively. Concentration of samples dried under variable temperature regimes resulted to higher CBD mean levels (+46.7% for inflorescences and +65.3% for leaves), while the Delta(9)-THC levels did not seem to be affected significantly at any drying treatment. Different constant temperature levels of isothermal drying or rates of temperature increase of non-isothermal drying, were not found to have a significant effect on the total content of the two investigated cannabinoids. Thus, non-isothermal drying at the maximum rate of temperature increase (4 degrees C.h(-1)) is proposed since reduced drying duration and energy consumption is achieved by retaining high CBD levels.