Tomato tablet drying enhancement by intervention of infrared - A response surface strategy for experimental design and optimization

In this study, the effects of hot air-infrared drying methods, including inlet air temperature, air velocity, and infrared power, are investigated on physical (color indices ΔL∗, Δa∗, and Δb∗, shrinkage, and unit density), mechanical (resistance to penetration), chemical (concentration of vitamin C and lycopene content), and thermal (effective moisture diffusivity coefficient) properties of compressed tablets made of tomato powder. The drying processes of the samples were investigated at five temperature levels of 40, 50, 60, 70, and 80 °C, five infrared power levels of 0 (without infrared), 500, 1000, 1500, and 2000W, and five inlet airflow velocity levels of 0.5, 1, 1.5, 2, and 2.5 m/s. Statistical analysis of the obtained data and optimization of the drying process was performed using the response surface methodology. The results showed that in hot air-infrared drying, with increasing the inlet air temperature, the concentration of vitamin C in tomato tablets decreased, and the lycopene content of tomato tablets increased. The optimum point for drying tomato tablets was obtained at an air temperature of 40 °C, air velocity of 2.5 m/s, and infrared power of 876.5 W. The highest percentage of vitamin C degradation occurred during the drying process of tomato slices at 50 °C. The results showed that drying at lower temperatures increased the desirability index of the model obtained from the response surface method.