Effect of temperature on moisture desorption isotherms of kheer

Desorption isotherms of kheer, a rice based partially heat concentrated and sweetened Indian milk dessert, were obtained in the temperature range of 10-40degreesC. The desorption curves exhibited sigmoid shape corresponding to type 11, typical of many foods. There was generally a negative temperature effect on EMC at low a(w), but curves at 25degreesC and 40degreesC showed inversion above water activity of 0.60 implying a higher equilibrium moisture content at higher temperature. Of the five sorption models tested, the GAB model gave the best fit at all the three temperatures. Besides monolayer moisture, properties of sorbed water viz. number of adsorbed monolayers, bound or nonfreezable water, density of sorbed water and surface area of sorption were also obtained. Isosteric heat of sorption obtained by applying Clausius-Clapeyron equation decreased exponentially with the increasing moisture content. (C) 2004 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved.