Mentha spicata drying via infrared: Mathematical modeling and evaluation of two-step temperature potential for improving drying characteristics

To assess the effects of a two-step temperature method (TTM) on dehydration parameters, color deterioration of dried samples, and specific energy consumption (SEC), spearmint leaves were dried using infrared (IR) undergoing the TTM. Moreover, 14 mathematical models were compared based on the adjusted correlation coefficient, reduced chi-square, and root mean square error to estimate drying curves. Changes in the color of the dried product at two-step temperatures of 70(to60 degrees C), 60(to50 degrees C), and 50(to40 degrees C) led to decreases of 2.69, .81, and 3.34 compared to fixed temperatures of 70, 60, and 50 degrees C, respectively. On the other hand, the specific energy consumption (SEC) increased by 5.43, 10.92, and 22 MJ.g(-1) H2O at 70(to60 degrees C), 60(to50 degrees C), and 50(to40 degrees C) compared to 70, 60, and 50 degrees C, respectively. To interpret the results from another point of view, three basic objectives of shortening drying time, reducing energy consumption, and raising the quality of the dried product are achieved in the TTM. For instance, the drying time and energy consumption are reduced at a two-step temperature of 70(to60 degrees C) compared to the fixed temperature of 60 degrees C, along with a decrease in the color change compared to the fixed temperature of 70 degrees C. The results indicated that Midilli et al. model resulted in the best fitness in explaining the IR drying behavior of spearmint leaves.