Experiment study on convective and radiation drying of Dahongpao Zanthoxylum bungeanum Maxim under different temperature and humidity
Inorder to compare the drying characteristics and quality of Dahongpao Zanthoxylum bungeanum Maxim(ZBM)under hot air drying,hot air-infrared drying and hot air-microwave drying methods,and reveal the thin layer drying process of convection-radiation combined drying to guide the production practice,the effects of hot air drying,hot air-infrared drying and hot air-microwave drying under the condition of different hot air temperatures(50 ℃,60 ℃,70 ℃)and different air relative humidity(10％,30％,50％)were analyzed by contrast with drying curve and effective moisture diffusivity.The drying kinetics was analyzed by combining the scale parameter(α),shape parameters(β)of Weibull function and the calculated moisture diffusion coefficient,the oil bud structure and volatile oil components of dried ZBM were analyzed by scanning electron microscope(SEM)and gas chromatography mass spectrometry(GC-MS)respectively.The results show that the drying time of hot air drying was longest.Increasing the temperature or decreasing the humidity was helpful to improve the drying rate and shorten the drying time,but it had little effect on hot air-infrared and hot air-microwave drying.Weibull function could well simulate the drying curves of three drying methods.The scale parameter(α)was related to the drying time and changed obviously with drying conditions.The shape parameter β＞1,it showed that water migration was jointly controlled by the surface and interior of the material.The calculated moisture diffusion coefficient variation ranges of the three drying methods were 1.303×10-7-2.815×10-7 m2/min、7.646×10-7-9.628× 10-7 m2/min、2.200×10-6-2.778× 10-6 m2/min respectively,and were related to the change of hot air temperature and humidity.Through SEM observation on the dried peel of ZBM,it was found that the structure of oil bud dried by hot air and hot air-infrared were well preserved,while oil bud was more full after hot air-microwave drying;and the content of volatile oil extracted from ZBM after hot air-microwave drying was the most(7.5％)by using GC-MS analysis,the relative content of olefins was the largest.The volatile oil extracted from ZBM by hot air drying was the lowest,but the volatile oil had the most kinds of compounds.Considering the quality and drying characteristics of dried Dahongpao ZBM,the hot air-infrared combined drying method was the better method.
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