Micrographs of lychee pericarp and pulp during microwave vacuum drying were tested and analyzed in order to illuminate the microstructure change of lychee and effect of the change on moisture removing in lychee.The re...Micrographs of lychee pericarp and pulp during microwave vacuum drying were tested and analyzed in order to illuminate the microstructure change of lychee and effect of the change on moisture removing in lychee.The results showed that the pericarp consisted of three parts:outer layer with cuticle,inter layer and inner layer.Outer layer and inter layer cells are easily destroyed than inner layer because of small and intact inner layer cells.Furthermore,micrographs showed that the moisture content of pulp keep constant with the temperature increasing at first 40 min due to the inner layer cells prevent the moisture removing from pulp.The long tubular structure of pulp cell would become break and lost over time,because the intercellular spaces reduced and the moisture removing was slow down in pulp.Meanwhile,the microstructure of lychee dried with temperature control was better than that without temperature control.展开更多
The drying kinetics of peppermint leaves was studied to determine the best drying method for them.Two drying methods include hot-air and infrared techniques,were employed.Three different temperatures(30,40,50℃)and ai...The drying kinetics of peppermint leaves was studied to determine the best drying method for them.Two drying methods include hot-air and infrared techniques,were employed.Three different temperatures(30,40,50℃)and air velocities(0.5,1,1.5 m/s)were selected for the hot-air drying process.Three levels of infrared intensity(1500,3000,4500 W/m^2),emitter-sample distance(10,15,20 cm)and air speed(0.5,1,1.5 m/s)were used for the infrared drying technique.According to the results,drying had a falling rate over time.Drying kinetics of peppermint leaves was explained and compared using three mathematical models.To determine coefficients of these models,non-linear regression analysis was used.The models were evaluated in terms of reduced chi-square(χ^2),root mean square error(RMSE)and coefficient of determination(R^2)values of experimental and predicted moisture ratios.Statistical analyses indicated that the model with the best fitness in explaining the drying behavior of peppermint samples was the Logarithmic model for hot-air drying and Midilli model for infrared drying.Moisture transfer in peppermint leaves was also described using Fick’s diffusion model.The lowest effective moisture diffusivity(1.096×10^-11m^2/s)occurred during hot-air drying at 30℃ using 0.5 m/s,whereas its highest value(5.928×10^-11m^2/s)belonged to infrared drying using 4500 W/m^2 infrared intensity,0.5 m/s airflow velocity and 10 cm emitter-sample distance.The activation energy for infrared and hot-air drying were ranged from 0.206 to 0.439 W/g,and from 21.476 to 27.784 kJ/mol,respectively.展开更多
基金the National Natural Science Foundation of China(No.31201399)Shenzhen Technology Innovation Program(No.JCYJ20140508155916427)Program for Science&Technology Innovation Talents in Universities of Henan Province(No.14HASTIT023)for the financial support of materials and the equipment.
文摘Micrographs of lychee pericarp and pulp during microwave vacuum drying were tested and analyzed in order to illuminate the microstructure change of lychee and effect of the change on moisture removing in lychee.The results showed that the pericarp consisted of three parts:outer layer with cuticle,inter layer and inner layer.Outer layer and inter layer cells are easily destroyed than inner layer because of small and intact inner layer cells.Furthermore,micrographs showed that the moisture content of pulp keep constant with the temperature increasing at first 40 min due to the inner layer cells prevent the moisture removing from pulp.The long tubular structure of pulp cell would become break and lost over time,because the intercellular spaces reduced and the moisture removing was slow down in pulp.Meanwhile,the microstructure of lychee dried with temperature control was better than that without temperature control.
文摘The drying kinetics of peppermint leaves was studied to determine the best drying method for them.Two drying methods include hot-air and infrared techniques,were employed.Three different temperatures(30,40,50℃)and air velocities(0.5,1,1.5 m/s)were selected for the hot-air drying process.Three levels of infrared intensity(1500,3000,4500 W/m^2),emitter-sample distance(10,15,20 cm)and air speed(0.5,1,1.5 m/s)were used for the infrared drying technique.According to the results,drying had a falling rate over time.Drying kinetics of peppermint leaves was explained and compared using three mathematical models.To determine coefficients of these models,non-linear regression analysis was used.The models were evaluated in terms of reduced chi-square(χ^2),root mean square error(RMSE)and coefficient of determination(R^2)values of experimental and predicted moisture ratios.Statistical analyses indicated that the model with the best fitness in explaining the drying behavior of peppermint samples was the Logarithmic model for hot-air drying and Midilli model for infrared drying.Moisture transfer in peppermint leaves was also described using Fick’s diffusion model.The lowest effective moisture diffusivity(1.096×10^-11m^2/s)occurred during hot-air drying at 30℃ using 0.5 m/s,whereas its highest value(5.928×10^-11m^2/s)belonged to infrared drying using 4500 W/m^2 infrared intensity,0.5 m/s airflow velocity and 10 cm emitter-sample distance.The activation energy for infrared and hot-air drying were ranged from 0.206 to 0.439 W/g,and from 21.476 to 27.784 kJ/mol,respectively.
