Moisture migration through fat-based multiphase systems

Moisture migration is one of the major problems in composite chocolate products. Moisture migration occurs in chocolate coated products with water-based filling. Moisture migration through fractionated palm kernel oil (PKO) based films under vapor-induced and liquid-induced conditions was investigated through measurement of unsteady-state diffusivity, steady-state permeability, and characterization of structure.; Water sorption isotherms were determined at 25°C for sucrose, lecithin, cellulose, PKO, and fat-based coatings (PKO+lecithin, PKO+sucrose, PKO+cellulose, PKO+sucrose+lecithin, PKO+cellulose+lecithin) using a gravimetric method in a water activity range of 0.112-0.974. Sucrose adsorbed much less moisture than lecithin and cellulose at water activities below its deliquescent point (0.85), but showed a sharp increase in water sorption capacity at higher water activities with phase change from crystalline to dissolved sucrose. Addition of lecithin, sucrose, or cellulose increased water sorption capacity of fat-based coatings.; At a water activity gradient of 1.0 (aw1=0.0; aw2=1.0) across fat-based films, addition of sucrose, cellulose, and lecithin significantly reduced the unsteady-state diffusivity but increased the steady-state permeability under both vapor-induced and liquid-induced conditions. For fat-based films containing sucrose, the unsteady-state diffusivity (P=0.001) and permeability (P=0.00) were significantly higher under liquid-induced condition than those under vapor-induced condition at a water activity gradient of 1.0 (a w1=0.0; aw2=1.0).; For pure PKO films, sucrose concentration of the aqueous phase (Diffusivity: P=0.98; permeability: 0.93) and presence of sugar ester (Diffusivity: P=0.76; permeability: P=0.12) in the aqueous phase had no effect on the diffusivity and permeability. For fat-based films containing sucrose, the unsteady-state diffusivity increased and the steady state permeability decreased (P=0.00) with increasing sucrose concentration of the aqueous phase.; This research provides some guidelines for product development of chocolate products with water-based fillings or chocolate flavored ice-cream coatings in terms of formula development, sweetener selection, and shelf-life prediction. Bi-layer formulation of chocolate is recommended to retard moisture migration. Sweeteners in fat-based films or coatings should have a deliquescent point higher than that of water-based filling because moisture migrates mainly through liquid phase. Permeability data obtained under liquid-induced moisture migration should be used to predict the shelf life when the chocolate shell or coating has water soluble components. (Abstract shortened by UMI.)...