In this study the moisture sorption isotherm of grape seed was determined by using a static gravimetric method at 35-65°C and 0.108-0.821 water activity range. The sorption isotherms were found to be typical sigmoid shape of most food materials. Five models including the Brunauer-Emmett-Teller (2-parameter), Guggenheim, Anderson and De Boer (3-parameter), Oswin (2-parameter), Ferro-Fontan (3-parameter) and Peleg (4-parameter) models were considered to fit the experimental data. The Ferro- Fontan and Peleg equations (at three temperatures 35, 45, 65°C) having R2 greater than 0.97 and lower values of standard error of estimate and deviation modulus gave the best fit of the experimental data throughout the entire range of water activity. The net isosteric heat of sorption, calculated by Calusius-Clapeyron equation on experimental data, was found to be a polynomial and exponential function of equilibrium moisture content within the temperature range investigated.
Sorption properties of some ingredients of muesli such as flakes and dried and candied fruits were investigated in this work. Kinetics of water vapor sorption at water activity of 1.00, 0,755, 0.239 and 0.00 was continuously measured. Kinetics of water sorption was well described by the solution of the Second Fick’s Law. However, the superficial values of equilibrium water content were obtained by kinetic measurements. The shape factor in the Fick’s equation was dependent on water activity. It was shown that in the analysed products adsorption process goes faster than the desorption one. Hence desorption of water from fruits and adsorption by flakes seems to be a limiting factor for water transfer in mixtures consisting of cereals and fruits.