Pulsed vacuum drying enhances drying kinetics and quality of lemon slices

The effect of drying temperature (60, 65, 70, and 75 degrees C) on drying characteristics, shrinkage, rehydration kinetics, microstructure and color profiles of lemon slices were investigated using a far-infrared radiation heating assisted pulsed vacuum dryer. Results showed that the drying time of lemon slices was reduced from 10.5 to 5.5 h when the drying temperature was increased from 60 to 75 degrees C. Weibull model could precisely describe the drying of samples under different drying temperatures (R-2>0.99). Moisture effective diffusivity (D-eff), which was determined by taking shrinkage effect into consideration, varied with moisture content. At the initial drying stages, the volume shrinkage of samples followed a linear relationship with decreasing moisture content as the volume shrinkage is approximately equal to the volume of evaporated water. Microstructure observation illustrated that the "skeleton" was fixed when moisture content decreased to approximate 60% w.b. Page model could well model the rehydration kinetics (R-2> 0.98). In terms of color evaluation, temperature of 75 degrees C significantly caused color deterioration and it recorded the highest color change (Delta E) of 14.23, Browning Index (BI) of 27.14 and lowest Hue Angle (H-0) of 79.46. The findings indicate that FIR-pulsed vacuum drying is a promising alternative method for lemon slices as it can enhance drying process as well as preserve the quality attributes of lemon slices. (C) 2018 Elsevier Ltd. All rights reserved.