Drying is an important postharvest step preceding long term storage of medicinal plants, and optimized drying conditions are critical for secondary metabolite preservation. The objective of this research was to determine the effect of pre-freezing, vacuum, drying temperature, and microwave power on cannabis, including drying kinetics, color retention, and moisture diffusivity, and cannabinoid and terpene concentrations. Harvested inflorescence was dried under four drying conditions, namely untreated, dried without vacuum, untreated, dried with vacuum, pre-frozen, dried without vacuum, and pre-frozen, dried with vacuum. The untreated groups were dried and analysed immediately after harvest and the pre-frozen group was frozen at −20C for 24 h prior to drying and analysis. Results showed that moisture diffusion was significantly affected by the temperature, vacuum and microwave power and reduced exponentially with time. For untreated samples dried at a microwave power of 2 W g, it took only 61 min (with no vacuum) and 57.3 min (under vacuum) at 65C to reach the desired final moisture content of 11 % dry basis. Increasing drying temperature from 35C to 50°C at 1 W g under vacuum reduced the drying time by 60.1 % and 68 % for pre-frozen and untreated samples, respectively and reduced by 68 % and 65.5 % for pre-frozen and untreated cannabis samples, respectively for samples dried without vacuum. Pre-freezing prior to hot air drying with and without vacuum can be used to preserve the color of biomass and cannabinoids. The effect was prominent in the acidic cannabinoids where pre-freezing prior to hot air drying at 50C without vacuum increased tetrahydrocannabinolic acid and cannabigerolic acid concentrations from 20.6 to 23.6 g 100 g dry matter and 0.47–0.61 g 100 g dry matter. Results presented add important knowledge for the optimization of postharvest steps for cannabis.

中文翻译：

---

微波辅助大麻热风干燥：真空和预冷冻对干燥动力学和质量的影响


干燥是药用植物长期储存之前的重要采后步骤，优化的干燥条件对于二次代谢物的保存至关重要。本研究的目的是确定预冷冻、真空、干燥温度和微波功率对大麻的影响，包括干燥动力学、保色性和水分扩散性以及大麻素和萜烯浓度。收获的花序在四种干燥条件下干燥，即未处理、无真空干燥、未处理、真空干燥、预冷冻、无真空干燥和预冷冻、真空干燥。未处理组在收获后立即干燥并分析，预冷冻组在干燥和分析之前在-20°C冷冻24小时。结果表明，水分扩散受温度、真空度和微波功率的显着影响，并随时间呈指数下降。对于在 2Wg 微波功率下干燥的未处理样品，在 65℃ 下仅需要 61 分钟（无真空）和 57.3 分钟（真空）即可达到所需的最终含水量 11% 干基。在真空下以 1Wg 将干燥温度从 35°C 提高到 50°C，预冷冻和未经处理的样品的干燥时间分别减少了 60.1% 和 68%，预冷冻和未经处理的大麻样品的干燥时间分别减少了 68% 和 65.5% ，分别适用于无真空干燥的样品。在使用或不使用真空的热风干燥之前进行预冷冻可用于保留生物质和大麻素的颜色。这种效果在酸性大麻素中尤为突出，在 50°C 无真空的情况下进行热风干燥之前进行预冷冻，可将四氢大麻酚酸和大麻二酚酸浓度从 20.6 克 100 克干物质增加至 23.6 克 100 克干物质，以及 0.47 至 0.61 克 100 克干物质。 所提出的结果为优化大麻采后步骤增加了重要知识。