Sorption isotherms and thermodynamics of water sorption of ready-to-use Basundi mix

Basundi mix representing powdered Basundi (an Indian traditional milk product somewhat similar to sweetened condensed milk) is a convenience product developed for enhanced shelf life at ambient temperature. Water sorption isotherms were obtained for this ready-to-use mix over the temperature range of 5–45 °C. There was definite inversion of the temperature effect at high water activity (>0.7). GAB model gave excellent agreement between experimental and predicted values. Other properties of sorbed water viz., monolayer water, number of adsorbed monolayers, density and amount of bound water and surface area of adsorption were also obtained. The net isosteric heat of sorption had strong dependence on moisture content. The enthalpy–entropy compensation suggested that the sorption mechanism involved is enthalpy driven over the entire range of moisture content studied.