Utility of heating pattern with variable air temperature in drying; effects on drying time, energy consumption, and product quality

Drying with variable air temperature is a technique to decrease the drying time, preserve quality and maintain the nutritional components of products. The aim of this study was to find the effect of different heating patterns with variable air temperatures on the drying time, energy consumption and the quality of garlic as well as investigate the critical times to change the air temperature. The constant air temperatures were 50, 60, and 70 degrees C, and the variable air temperature included three patterns of 60 degrees C -> 50 degrees C (I), 70 degrees C -> 50 degrees C (II), and 70 degrees C (30 minutes) -> 50 degrees C (III). Despite preventing garlic slices' color changes in the constant air temperature of 50 degrees C, the antioxidant contents of the samples reduced significantly (45%), and the drying time was 136 minutes. At the air temperature of 70 degrees C, the color changes peaked, and the drying time was 65 minutes. The best drying condition was observed among the variable air temperature by pattern III. The drying time and loss of antioxidants were 24% and 45% lower than the one in the constant air temperature of 50 degrees C; besides, the effective moisture diffusivity was 24% higher. The color changes of these samples were lower compared to other patterns and the final product had acceptable quality and was produced in an optimal time.