Experimental and numerical study on the shrinkage-deformation of carrot slices during hot air drying

In order to further understand the mechanism of material volume change in the drying process,numerical simulations(considering or neglecting shrinkage)of heat and mass transfer during convective drying of carrot slices under constant and controlled temperature and relative humidity were carried out.Simulated results were validated with experimental data.The results of the simulation show that the Quadratic model fitted well to the moisture ratio and the material temperature data trend with average relative errors of 5.9%and 8.1%,respectively.Additionally,the results of the simulation considering shrinkage show that the moisture and temperature distributions during drying are closer to the experimental data than the results of the simulation disregarding shrinkage.The material moisture content was significantly related to the shrinkage of dried tissue.Temperature and relative humidity significantly affected the volume shrinkage of carrot slices.The volume shrinkage increased with the rising of the constant temperature and the decline of relative humidity.This model can be used to provide more information on the dynamics of heat and mass transfer during drying and can also be adapted to other products and dryers devices.

Effects of pulsation ratio on center temperature and drying characteristics of pineapple slices with pulsed vacuum drying

This research explored the application of pulsed vacuum technology on the drying(PVD)of pineapple slices.Influences of drying temperature and pulsed vacuum ratio(PVR)on drying characteristics and pineapple quality(color,rehydration characteristics,microstructure,and texture)were analyzed.As expected,increasing the drying temperature resulted in a higher drying rate and effective moisture diffusivity.The optimal PVR of 5:5 was beneficial in accelerating the drying rate of pineapple slices and the corresponding effective moisture diffusion coefficient(8.9601×10^(-10))was higher than other PVR conditions based on material center temperature.The material temperature increased during the normal pressure period and decreased rapidly when the pressure dropped to the vacuum condition,which indirectly reflected the moisture transfer that occurred during the vacuum holding period,while moisture diffusion happened during the atmospheric pressure holding period.The optimal pulsed vacuum drying process(PVR of 5:5)could expand air and water vapor and create a looser structure so as to obtain better rehydration performance(rehydration ratio(RR)was 5.43).High drying temperature led to the decrease of L^(*)value,the increase ofΔE value,and even the formation of surface scorch at 80℃.At the same drying temperature,the color quality depended on the drying time,and the color difference increased with the extension of the drying time.The chewiness and hardness of pineapple slices dried by PVD were significantly higher than those of fresh samples,which was conducive to the chewing taste.