Freeze-drying Cannabis sativa L. using real-time relative humidity monitoring and mathematical modeling for the cannabis industry

Abstract

Pre-freezing has an impact on the drying time and physiochemical properties of cannabis. This study investigated the relationship between sample mass reduction and relative humidity during freeze-drying and the effects of pre-freezing and freeze-drying temperature on cannabis drying kinetics, trichome structure, and color, in addition to cannabinoid and terpene concentrations. Three cannabis accessions, Qrazy Train, Qrazy Apple, and Qrazy Angel, were dried at 10°C, and 20°C, with different pre-freezing conditions (−20°C and −40°C). Pre-freezing rates of 0.13°C min−1 for both Qrazy Train and Qrazy Angel and 0.15°C min−1 for Qrazy Apple were recorded for pre-freezing at − 20°C and significantly (p < 0.05) increased by 73.5%, 71.2%, and 72.9% for Qrazy Train, Qrazy Apple, and Qrazy Angel, respectively, when inflorescence was pre-frozen at − 40°C. Rational regression model best explains the relationship between mass reduction and relative humidity during drying, while drying kinetics can be described using the Page and Logarithmic models. Total color changes ranged from 1.16 to 9.69 total color changes measured for all dried samples compared to respective fresh, undried samples were not significantly (p < 0.05) different. THCA concentrations for fresh, undried Cannabis sativa L. accessions ranged from 214.4 mg g−1 to 257.5 mg g−1; this was higher than their CBDA concentrations, ranging from 0.03 mg g−1 to 0.1 mg g−1. Freeze-drying increased [CBDA], [CBGA], and [CBG] in dried samples ranging from 0.45 mg g−1 to 0.38 mg g−1, 2.87 mg g−1 to 4.91 mg g−1, and 0.57 mg g−1 to 1.33 mg g−1, respectively. Mean terpene concentration ranged from 17.7 mg g−1 to 40.3 mg g−1. Irrespective of the pre-freezing condition or cannabis accession, drying at 20°C reduced drying time by 10.4–31.9%. Findings could be of industrial relevance for improving post-harvest processes while maintaining quality of this regulated crop.