ABSTRACT
Objective: Taking Panacis Quinquefolii Radix (PQR) as study object, the drying characteristic and quality was investigated under constant relative humidity (RH) and step-down RH drying method in order to provide foundation for improving drying efficient and quality of PQR. Methods: At drying temperature 55 ℃, the effect of constant RH (20%, 30%, and 40%), step-down RH, when RH 40% was kept for 1, 5, and 9 h and then decreased to 20%, and continuously dehumidification drying conditions on drying characteristic, moisture effective diffusion coefficient, rehydration ratio, shrinkage ratio, total ginsenoside content and microstructure were investigated. Results: With constant RH drying condition, the lower the RH was, the higher the drying rate was. When RH was 20%, the drying time was shortened by 6.8% compared with RH of 40%. With step-down RH drying condition, when RH 40% was held for 5 h and then decreased to 20%, the drying time was shortened by 3.4% compared with dehumidification drying method. Also, a transient increasing drying rate phase was appeared. Moisture effective diffusion coefficient ranged from 1.49 × 10-10 to 2.50 × 10-10 m2/s. Rehydration ratio mainly depended on the damage degree of the PQR cellular structure and the moisture content before rehydrating. Additionally, the rehydration ratio and shrinkage ratio increased with the increase of RH. High RH was benefit for reserving and transferring of ginsenoside content. The microstructure results showed that under continuous dehumidification drying process, the PQR surface was crusted so that the drying time was prolonged and rehydration ratio was decreased. On the other hand, step-down RH drying method was benefit for porous structure formation, which was helpful for shortening drying time and improving rehydration ratio. When RH 40% was kept for 5 h and then decreased to 20%, the comprehensive score of this drying condition achieved its maximum value as (0.61 ± 0.01). Such drying condition was regarded as the best drying process with the rehydration ratio, shrinkage ratio and total ginsenoside content of 2.23 ± 0.12, 0.26 ± 0.06, and (5.01 ± 0.04)%, respectively. Conclusion: Step-down RH drying method can improve PQR drying efficient and quality and such conclusion provided theoretical foundation and technical support for how to adjust RH during hot air drying of PQR.
ABSTRACT
Objective: Taking single Liuwei Dihuangwan(LDW) as the research object,the moisture content change and volumetric shrinkage characteristics in its drying process were investigated,which provided the theoretical basis for improving the drying efficiency of the pills and reducing the quality problems of the pattern pills,crusts and crack pills. Method: The drying characteristics of LDW at drying temperature of 50,75,100,125℃ were studied by constant temperature hot air drying and vacuum drying.Based on sphere model of Fick's second law and Arrhenius equation,the effective diffusion coefficient and activation energy of the drying process were obtained.The volumetric shrinkage characteristics of the pills during the drying process were studied by the projected area method.The Weibull function was used to fit the drying dynamics curve of single LDW. Result: Hot air drying and vacuum drying of LDW both belonged to the decreasing drying processes,and the time required to achieve the same moisture content in vacuum drying was shorter than that in hot air drying.The moisture ratio in the drying process of single LDW obeyed the Weibull function distribution(R2=0.994 5-0.999 7),the scale parameter(α) decreased with the increase of temperature,and drying temperature had significant influence on the shape parameter (β).The effective diffusion coefficients of hot air drying and vacuum drying were 2.626×10-3-7.823×10-2,3.782×10-3-9.042×10-2 m2·s-1, their activation energy were 47.18,42.69 kJ·mol-1,respectively.The volume ratio of hot air drying and vacuum drying of LDW ranged from 0.638 to 0.741 and 0.607 to 0.689,respectively. Conclusion: Weibull function can be adopted to predict the drying and dehydration law of LDW.Under the condition of low temperature drying,slow-down of shrinkage rate of the pills is helpful to prevent the formation of splitting pills,this study provides theoretical and technical basis for dying of LDW.