Sorption isotherms and moisture sorption hysteresis of intermediate moisture content banana

Sorption isotherms of dried or intermediate moisture content (IMC) products are most important to model moisture uptake during storage and distribution. Working isotherms of IMC bananas were determined at five different temperatures (10, 15, 20, 30 and 40 degrees C). Desorption and adsorption isotherms were determined at 10 and 40 degrees C. All the sorption curves were found to be Type 11, with non-zero moisture content (approximately 3-9% db for different temperatures) when the water activity was zero. Different models were fitted to the data and it was found that the best results were obtained with a modified Freundlich equation (valid from 0.06 to 0.76 water activity). The dependence of the models constants on temperature was investigated and the secondary models were built accounting for the effect of a, and temperature on the samples moisture content (R-2 = 99%). Hysteresis was observed at 10 degrees C and 40 degrees C, but the effect was greater at 10 degrees C. The net isosteric heat of sorption (working isotherms) varied from 0.85 kJ g(-1) mol(-1) to 7.67 kJ g(-1) mol(-1), decreasing with increasing moisture content. This effect was well described by an exponential function (R-2 > 99%). These results provide reliable experimental data on sorption isotherms which is important for designing an optimized packaging system. (C) 2007 Elsevier Ltd. All rights reserved.