Drying characteristics of Chaenomeles sinensis with different drying methods based on Dincer model / 中草药

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.