MOISTURE SORPTION ISOTHERM, PROPERTIES OF SORBED WATER AND HEAT OF SORPTION OF SANDESH - AN INDIAN MILK PRODUCT

Moisture sorption isotherm of sandesh, one of the most popular milk products in India, was determined in terms of its moisture adsorption isotherms by gravimetrical method at 20 and 30C using various saturated salt solutions in the range of 11.2 to 97.2%. The isotherms obtained were of sigmoid shape and of the Brunauer-Emmett-Teller type. Out of three sorption models fitted to the experimental data, Caurie's model was found superior in interpreting the moisture adsorption characteristics of sandesh. The monolayer moisture content as calculated from the Caurie's model at 20 and 30C were 5.89% (dry basis [d.b.]) and 5.21% (d.b.), respectively. The values of isosteric heat of sorption as calculated from Clausius-Clapeyron equation was found to increase with decreasing moisture content at lower moisture content and approached the value of heat of vaporization of free water above 17.25% (d.b.).