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 (Deff), the glass transition temperature (Tg), 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 (Tm) 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 (Ta), the surface temperature of the garlic (Ts), the internal temperature of the garlic (Ti), and the weight of the garlic slices were measured and recorded in real time. The Deff was calculated using the slope method. A higher drying rate was observed in the AC drying treatment. The Tg variations were associated with the Ti and moisture content of the garlic. The drying time (ts) for the AC and the DC heating-cooling profiles was found to be between 180 to 238 min.