Modeling incidence of lipid and sodium chloride contents on sorption curves of gelatin in the high humidity range

Water mobility and availability are predominant factors in controlling organoleptic and biological quality in food. To characterize and quantify the role of protein macromolecular mesh, sodium chloride and fat on the water retention in the high humidity range, sorption isotherms were measured at 20 °C. A specific method was used which provides rapid equilibrium and many experimental points in comparison with the standard saturated salt solution method. Experiments were carried out on gelatin gels to which either sodium chloride (0–45% w/w on an anhydrous gelatin basis) or vegetal hydrogenated fat (0–50% w/w on total sample mass) was added. Desorption isotherms of 40 points each were measured for each sample for aw values in a range from 0.60 to 0.99. Results precisely show the specific behavior of water in a protein–sodium chloride mix for aw values between 0.65 and 0.75. Water activity was then predicted from sample composition. Good agreement with measurements was obtained (1) assuming no incidence of lipids on water-holding capacity and (2) adapting a Ross-type model considering crystallization and introducing an interaction factor related to sodium chloride content.