Investigation of moisture sorption behavior of soluble sodium caseinate

Casein is a potential food protein, used in a number of food applications. In this work, moisture sorption isotherms of casein were determined at 10, 20 and 30°C under different relative humidity in the range of 12 to 98% using gravimetric method. The equilibrium moisture uptake data were interpreted with the help of three well-known sorption isotherm models namely, (GAB, Halsey and Oswin models) using non-linear least square method. The experimental moisture uptake data were best interpreted by GAB model. The monolayer moisture content Xm was found to vary from 54.08 x 10^-3 to 10.48 x10^-3 kg kg^-1 (db) for a temperature rise from 10 to 30°C, thus indicating negative temperature dependence. The Clausius-Clapeyron equation was used to determine the isosteric heat of sorption (qst). The uptake data was also used to determine isokinetic temperature Tβ (315.9 K) and harmonic mean temperature Thm (292.8 K). The enthalpy-entropy compensation theory indicated that moisture sorption process was enthalpy driven.