Moisture sorption characteristics of chhana podo at 5 °C and 35 °C

The equilibrium moisture contents (EMC) of chhana podo were determined using the static gravimetric method, at 5 °C and 35 °C, over a range of water activity from 0.23 to 0.98. The isotherms obtained were of sigmoid shape, and of BET type II classification. The EMC, at a given water activity, decreased as the temperature increased from 5 °C to 35 °C. Amongst the 12 sorption models tested, the Caurie’s model best described the EMC/water activity relationship of chhana podo by giving a closest fit to the experimental sorption data. The suitability of the models was tested and compared by estimating the coefficient of determination (R2) and mean relative per cent deviation modulus (P). The sorption data were analyzed for the determination of monolayer moisture content, density of sorbed water, number of adsorbed monolayers, per cent bound water and surface area of adsorbent. The isosteric heat of sorption of water at different moisture contents was determined using the Clausius–Clapeyron equation. The net isosteric heat of chhana podo ranged from 0.081 kJ mol−1 at 42% moisture content (db) to 17.26 kJ mol−1 at 2% moisture content.