SECADO CONVECTIVO DE AJO (Allium sativum, L.) CON CONDICIONES VARIABLES DE OPERACIÓN

Abstract

Garlic is a biological material highly sensitive to temperature changes. During the drying process, cellular structure is fragmented, resulting in the formation of volatile bio-active compounds. These changes in internal structure are reflected in changes in the structural properties (true density, apparent density and porosity). However, these structural properties have often been expressed only in terms of moisture content (Lozano, Rostein and Urbicain 1983; Madamba, Driscoll and Buckle 1994) and have seldom been reported as a function of both drying air temperature and moisture content. These functions are not enough to explain the non-linearity of density at low water contents. The aim of this study was to study the effect of non-isothermal drying (trapezoidal wave profile at different wave periods: 60, 80, 120 and 160 min) and isothermal (at 40, 50 and 60 °C) on the quality deg radation of garlic during drying. True density (rp), apparent density (rb), porosity (e), glass transition temperature (Tg), surface temperature (Ts), inside temperature (Ti), moisture content (X), effective diffusivity (D) and cracking were analyzed in sliced garlic (initial thickness 2 ± 0.25 mm) in order to derive equations that describe the behavior of these structural variables and aid in the identification of the appropriate time to stop the drying process. A critical point in the intersection of Ti, Ts and Tg was found; this point was identified as a second order phase transition. Diffusivity and slope changes in rb, rp and e with respect to moisture content were found to be related to this critical point. Experimental data for rb, rp and e were fitted to a non-linear equation with three exponential terms with respect to moisture content, with an R2 > 0.85. A semi-empirical model for predicting changes in particle density during the drying process was obtained, with an R2 = 96.34.