Effect of Temperature on Sorption Isotherms and Thermodynamics of Intermediate Moisture Category Indian Milk Product Cham-cham

Abstract

Cham-cham, a traditional Indian milk product prepared by heat and acid coagulation of milk, has a shelf life of a few days. Its storage stability could be studied by monitoring the changes in water activity at different temperatures and humidity. Hence, moisture sorption characteristics of cham-cham were determined at three temperatures i.e., 5, 25 and 40C to obtain sorption isotherms. The data obtained were fitted to several models in which BET (Brunauer–Emmett–Teller), Modified Mizrahi and Henderson model gave best fit. From the BET equation, monolayer moisture content calculated at 5, 25 and 40C were 24.27, 15.60 and 18.25%, respectively. Density of sorbed water, number of adsorbed monolayers, percent bound water and surface area of adsorbent were calculated. The porosity of cham-cham increased with increase in temperature. The net isosteric heat of sorption decrease exponentially with increasing moisture content and enthalpy–entropy compensation theory confirmed the process to be spontaneous and enthalpy driven. Practical Applications The equilibrium moisture content, monolayer moisture content, net isosteric heat of sorption and related properties calculated can be used to represent the state of water present in cham-cham at different temperatures for physicochemical and microbiological changes. These results could successfully be utilized in predicting water activity values of cham-cham at different temperature and moisture content. The predicted water activity values may prove successful in studying and enhancing the shelf life of cham-cham by designing the production process and packaging material for cham-cham making and packaging.