Simultaneous Drying and Microbial Inactivation of Industrial Hemp (Cannabis sativa L.) Using Infrared and Hot Air Heating

Abstract

<b><sc>Abstract.</sc></b> The goal of this study was to study the feasibility of simultaneously drying and microbial inactivation of industrial hemp (Cannabis sativa L.) while preserving the cannabinoids. Hemp inflorescence and leaves from Queen-Dream-CBD variety were dried with hot air (65 and 85°C) and with sequential infrared and hot air drying (infrared pre-drying for 1 and 2 min, then completing drying with hot air at 65°C). Conventional natural drying was performed with indoor ambient air and used as a control. The drying time was decreased from 3366 min by conventional natural drying to as low as 222 min by hot air drying at 85°C to reduce the moisture content of hemp from about 0.75 to 0.10 kg water/kg wet mass, and the average drying rate increased from 9.16 x 10^-4 to 1.34 x 10^-2 kg water/kg dry mass/min accordingly. The load levels of total aerobic bacteria, and total yeast and mold in fresh hemp biomass were 4.63 and 4.75 log CFU/g, respectively, and conventional indoor drying resulted in 0.41 and 0.24 log CFU/g increase in the bacteria and mold levels, respectively. Thermal drying by hot air and infrared reduced the bacteria and yeast/mold load levels by up to 0.81 and 1.85 log CFU/g, respectively. The thermal drying also inactivated the enzyme activities of polyphenol oxidase and peroxidase by up to 91.7% and 66.7%, respectively, under hot air drying at 85°C. Meanwhile, the yield of total CBD in the thermally dried hemp was more than 96.1%, which was similar to the control. The results suggested that high-temperature hot air and infrared heating could efficiently dry the industrial hemp and effectively inactivate the microorganisms without negatively affecting the total CBD yield.