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: Based on Dincer model, the drying characteristic of Chaenomeles sinensis under different drying condition was investigated in order to provide theoretical foundation for applying Dincer model to analyze heat and mass transfer during Chinese herbs drying process and select suitable drying technology and process. Methods: C. sinensis slice of thickness 12 mm was dried by the three different drying methods, namely air impingement drying, medium and short infrared waved drying and pulsed vacuum drying. Also, 9, 12 and 15 mm C. sinensis slices were dried under air impingement drying method. The drying characteristic, color value, rehydration ration, vitamin C (VC), general flavone, and microstructure were studied. Results: At the same drying temperature, the drying rate sorted in order of size was air impingement drying, medium and short infrared waved drying and pulsed vacuum drying and the drying activation energy was 43.10, 36.95 and 20.37 kJ/mol in corresponding. Decreasing slice thickness enhanced drying rate. The Weibull distribution model simulation result showed that the scale parameter α ranged from 47.85 to 324.51. Smaller α value meant short drying time. The shape parameter β was between 1.218 7 and 1.290 8 under air impingement drying as well as medium and short infrared waved drying method, which showed that drying was falling rate process controlled by internal moisture diffusion. However, the shape parameter β was between 1.218 7 and 1.290 8 under pulsed vacuum drying method, which illustrated that drying was controlled both by internal moisture diffusion and surface moisture evaporation. The calculated moisture diffusion coefficient was ranged from (1.66 × 10-8) to (1.13 × 10-7) m2/s and decreased as α increased. The Dincer model simulation result showed that the lag factor (G) was range from 1.135 6 to 1.337 6, which declared that there was a short raising rate drying period during the initial drying process. Heat transfer Biot number (Bi) value was between 1.171 4 and 136.041 2 and decreased as drying temperature increased. Effective moisture diffusion (Deff) value calculated by Diner model was range from (3.26 × 10-9) to (6.33 × 10-8) m2/s. At the same drying temperature, (Deff) value was larger than (D*), but smaller than (Dcal). Mass transfer (k) was ranged from (9.02 × 10-6) to (8.82 × 10-5) m/s and increased as drying temperature increased. Air impingement drying method was suitable for C. sinensis slice drying, and drying temperature of 60 ℃ and thickness of 12 mm was the most optimum drying process. Under above drying circumstance, the drying time, brightness L*, color difference value ΔE, VC, general flavone and rehydration ratio were 5 h, 62.80 ± 1.70, 19.62 ± 2.60, (1.107 8 ± 0.005 0) mg/g, (36.74 ± 0.60) mg/g and 7.11 ± 0.24, respectively. Conclusion: Such investigation result can provide theoretical foundation for applying Dincer model to describe heat and mass transfer characteristics during Chinese herbs drying and filtrating suitable C. sinensis slice drying method and process.
ABSTRACT
Objective To mitigate Lycii Fructus surface crust and save drying time during drying process, vacuum pulsed drying technology was applied to dry Lycii Fructus so as to investigate moisture diffusion regulation and build the drying model. Methods The effect of different drying temperature (50, 55, 60, and 65 ℃), vacuum pressure holding time (5, 10, 20, and 30 min), and atmosphere pressure holding time (2, 4, and 8 min) on drying characteristics, moisture diffusion coefficients and drying activation energy was explored in vacuum pulsed drying process. Weibull model distribution was used to simulate and analyze Lycii Fructus drying curves. Results All the drying temperature, atmosphere pressure holding time, and vacuum pressure time holding time had significant influence on drying time. When drying temperature, atmosphere pressure holding time, and vacuum pressure time holding time was 60 ℃, 4 min, and 10 min, respectively, the minimum drying time was achieved to be 284 min. Weibull distribution model can be well described the vacuum pulsed drying process of Lycii Fructus. The scale parameter was related to drying time and decreased as drying temperature increased. The drying temperature, atmosphere pressure holding time, and vacuum pressure time holding time had little influence on the shape parameter. The shape parameter was associated with drying method. The moisture diffusion coefficient and activation energy were calculated to be 2.02 × 10-8-3.56 × 10-8 m2/s and 36.27 kJ/mol, respectively. Conclusion Weibull distribution model can well describe the moisture diffusion regulation of vacuum pulsed drying process of Lycii Fructus. The drying result had a great significance for predicting, controlling and optimizing drying process. On the other hand, the research could provide technical basis for industrial drying of Lycii Fructus by vacuum pulsed drying technology.