MOISTURE SORPTION ISOTHERMS AND THERMODYNAMIC PROPERTIES OF WHEY PROTEIN CONCENTRATE POWDER FROM BUFFALO SKIM MILK

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.