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SummaryMoisture sorption isotherms of khoa were determined at 15, 25, 35 and 45 °C over a water activity (aw) range of O·l 1–0·97. The isotherms were sigmoid (Type II) and were fitted to the Guggenheim–Anderson–de Boer (GAB) equation (Bizot, 1983). The aw of freshly made khoa was found to be 0·96. The aw of khoa increased with increasing temperature up to 0·9; above this the effect of temperature on aw diminished. The monolayer moisture content of khoa decreased with increasing temperature. The equations describing the temperature dependence of GAB constants were determined in the form of the Clausius–Clapeyron equation. The net isosteric heat of desorption of khoa decreased rapidly until a moisture level of 0·1 g/g solids, and approached a constant value of 0·43 kJ/mol above a moisture level of 0·25 g/g solids.

Adsorption and desorption isotherms of whey protein concentrate powder prepared from buffalo skim milk were determined at 25, 35 and 45C, over a water activity range of 0.11–0.97, using static moisture gain/loss from test samples. Both the adsorption and the desorption isotherms exhibited sigmoid shape corresponding to type II, typical to many foods. There was generally a negative temperature effect on equilibrium moisture content. The Guggenheim–Anderson–de Boer model gave the best fit for the sorption data throughout the entire water activity range and at all three temperatures. The monolayer moisture content values were higher in desorption than in adsorption and deceased with an increase in temperature. Isosteric heat of sorption and the entropy data displayed a strong dependence on moisture content. The adsorption data gave lower values than the corresponding desorption data. Temperature of sorption had profound influence on the properties of bound water and surface area of adsorbent. Practical Applications Dried milk products are the important segments of dairy industry. Whey is a by‐product of cheese, paneer or casein production, and is a source of best‐quality proteins. Indian subcontinent is the largest producer of buffalo milk in the world, and the indigenously available whey is mostly obtained from buffalo milk products. The results of the present study would have practical applications in exploiting the competitive advantages of buffalo milk and in developing high‐protein multicomponent functional foods using buffalo skim milk whey protein concentrate powder. The analysis of moisture sorption characteristics and thermodynamic properties of bound water would provide information regarding process energy requirements, shelf life appraisal and design of suitable packaging systems for the product.

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