Effects of drying air temperature on the structural properties of garlic evaluated during drying

Second order phase transitions may occur in foodstuffs during the convective drying process. These transitions involve physicochemical changes, which influence both structural properties and drying behavior. The aim of this study was to examine the effects of drying air temperature and the second order phase transition of garlic on the changes in particle density, apparent density, apparent porosity, effective diffusivity, and cracking produced during drying. Garlic slices were dehydrated at three air temperatures (40, 50, and 60°C). The moisture content (X), inside temperature (Ti), surface temperature (Ts), apparent (ρb) and particle (ρp) densities of garlic slices were measured during drying. Porosity (ε) was calculated based on the data collected for ρp and ρb. Glass transition temperatures (Tg) and micrographs were obtained for both raw and dehydrated garlic. 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 ρb, ρp, and ε with respect to moisture content were found to be related to this critical point. Experimental data for ρb, ρp, and ε was fitted to a nonlinear equation with three exponential terms with respect to moisture content, with an R² > 0.85. Less dense products were found to be more porous, with more cracking, higher moisture diffusivity, and lower Tg at the end of the drying process.