Changes in thermal properties of apple due to vacuum impregnation

Experimental determination and predictive equations are used to evaluate th e effect of vacuum impregnation with sucrose solutions on thermal propertie s of apple samples (Granny Smith). Vacuum impregnation (VI) was carried out by immersion of samples in the sucrose solution and applying 50 mbar in th e tank for 10 min; afterwards, atmospheric pressure was restored while samp les remain immersed for 20 min. Thermal diffusivity was measured in non-imp regnated (NVI) and impregnated samples in a transient heat conduction metho d. Thermal diffusivity changes due to VI were relatively low, whereas condu ctivity changes, calculated from thermal diffusivity, density and specific heat, showed very important changes. The proposed predictive model allows u s to estimate changes in thermal properties due to VI in terms of product p orosity and pore distribution and conditions of VI process. (C) 2000 Elsevi er Science Ltd. All rights reserved.