Non-isothermal drying of garlic slices (Allium sativum, L.): Wave period and initial temperature of the heating/cooling effect

Intermittent drying is a common technique for food conservation. The objective of this work is to evaluate the effect of non-isothermal drying and the wave periods using the effective diffusivity (D_eff), the glass transition temperature (T_g), their relationship to moisture content and the temperature of the product, as parameters for controlling quality deterioration. The heating–cooling profile was developed as a trapezoidal wave form using three different wave periods (τ:60, 120 and 160 min), with a midpoint temperature (T_m) of 50 °C and ∆T = 10 °C. The ascending (AC) heating–cooling treatment began at 40 °C, and the descending (DC) heating–cooling treatment began at 60 °C. The drying temperature (T_a), the surface temperature of the garlic (T_s), the internal temperature of the garlic (T_i), and the weight of the garlic slices were measured and recorded in real time. The D_eff was calculated using the slope method. A higher drying rate was observed in the AC drying treatment. The T_g variations were associated with the T_i and moisture content of the garlic. The drying time (t_s) for the AC and the DC heating–cooling profiles was found to be between 180 to 238 min.