目的 探索阶段降湿中高湿保持时间及不同降湿工艺对山药热风干燥特性和品质的影响，为提高山药干燥效率和品质及揭示相对湿度的调控依据提供理论基础。方法 研究干燥温度60℃，风速3.0 m/s，相对湿度恒定10%、50%保持不同时间（5、10、20 min）后降为10%、以及相对湿度50%保持10 min后不同降湿干燥工艺（直接降为10%、20%保持20 min后降为10%、30%，20 min，20%，20 min后降为10%、40%，20 min，30%，20 min，20%，20 min后降为10%），山药片的干燥特性、水分有效扩散系数（D_eff）、色泽、复水比、能耗、多糖含量和微观组织结构。结果 高相对湿度不同保持时间下，相对湿度50%保持10 min相对于恒定10%干燥条件下，干燥时间缩短了20.0%；干燥过程分为升速和降速2个阶段；在10 min时，山药片被充分预热，温度升至45.8℃。不同降湿干燥工艺下，相对湿度50%保持10 min后，阶梯降至10%相对于直接降为10%的干燥条件，干燥时间缩短了25.0%；干燥过程同样分为升速和降速2个阶段；物料温度整体上呈现出缓慢上升的趋势，且均大于其余3者同时期的物料温度；D_eff先慢后快，整个干燥过程平均D_eff最大，为6.77×10^-10 m²/s；此干燥条件下明亮度（L^*）、复水比和多糖含量分别达到其最大值，为（90.76±0.12）、（2.36±0.08）、（57.32±0.21）mg/g，能耗达最低值，为（2.98±0.06）kW·h/kg，且内部形成较明显的水分扩散迁移孔道。结论 高相对湿度有助于强化对物料的传热作用，保持时间应当以物料充分预热为判定依据；阶段降湿干燥过程中，降低相对湿度应当以不降低物料温度为基本约束条件；山药片的恒温阶段降湿干燥过程中，干制后的色泽、复水性、能耗和多糖含量均与干燥时间直接相关；高相对湿度有助于保持和形成物料内部的多孔结构，有助于水分的扩散迁移；依次阶段降湿的干燥方式有助于提高山药片的干燥效率和品质，为山药热风干燥过程中如何调控相对湿度提供理论依据和技术支持。

Objective In order to improve the drying efficient and quality of Dioscoreae Rhizoma slices and reveal the relative humidity (RH) control principle, the influence of different keeping time of high RH and different dehumidification humidity process on drying characteristic and quality of hot air drying of Dioscoreae Rhizoma slices were investigated. Methods With drying temperature 60 ^oC and air velocity 3.0 m/s, the influence of constant 10% RH, different 50% RH keeping time (5, 10, and 20 min) then decreasing to 10% as well as different dehumidification RH when 50% was kept 10 min (decreased to 10% directly; 20%, 20 min then 10%; 30%, 20 min, 20%, 20 min then 10%; 40%, 20 min; 30%, 20 min; 20%, 20 min then 10%) on drying characteristic, moisture effective diffusion coefficient (D_eff), color value, rehydration ratio, energy consumption, polysaccharide content and microstructure were studied. Results Under different high RH keeping time, when RH 50% was kept for 10 min and then decreased to 10%, the drying time was shorted by 20.0% compared to constant 10% RH drying condition. The drying process was divided into increasing and decreasing drying rate stage. The Dioscoreae Rhizoma slices were fully preheated and the temperature rose to 45.8 ^oC at 10 min. Under different dehumidification RH drying conditions, when 50% RH was kept for 10 min and then decreased to 10% successively, the drying time was shorted by 25.0% compared to when 50% RH was kept for 10 min and then decreased to 10%. The drying process was also divided into increasing and deceasing drying rate stage. On the whole, the material temperature showed a slow rising trend and was more than the other three drying conditions at the same time. D_eff was slow at first and then became quick and the average D_eff was the largest as to be (6.77×10^-10) m²/s. The brightness value (L^*), rehydration ratio (RR) and polysaccharide content were all achieved their maximum value as to be (90.76 ±0.12), (2.36 ±0.08), and (57.32 ±0.21) mg/g, respectively. At the same time, the energy consumption achieved its minimum value as to be (2.98 ±0.06) kW·h/kg. Additionally, the mercreature showed that the porous structure was formed which was benefit for internal moisture diffusion. Conclusion High RH is helpful to strengthen the materials heat transfer process, and the retention time should be based on the full preheating of materials. During dehumidification drying process, the basic constraint condition should be not to reduce the material temperature when reducing RH. In the process of step-down RH drying process with constant temperature stage, the color value, rehydration ratio, and polysaccharide content after drying were directly related to drying time. High RH helps to maintain and form the porous structure inside the material, which is conducive to the diffusion and migration of water. The drying method of step-down RH by successive stages is helpful to improve the drying efficiency and quality of Dioscoreae Rhizoma slices, which provides theoretical basis and technical support for the control of RH in the hot air drying process of Dioscoreae Rhizoma slices.

R283.6

北京市自然科学基金项目（6204035）；北京市教委组织部优秀人才项目（2018000020124G034）；河北省自然科学基金资助项目（C2020207004）；河北省高等学校科学技术研究项目（QN2021054）；河北经贸大学校级教学研究项目（2020JYY47）；河北经贸大学“生物工程”专项项目（2021SGYB03）