Abstract
Equilibrium and dynamic water sorption properties of sponge cakes with varying porosity (86–52%) and fat content (0–0.30 g/g d.b.) were determined using a water vapour sorption microbalance. Contrary to porosity, addition of fat decreased equilibrium moisture contents. The effective moisture diffusivity (Deff) was identified from a numerical solution of Fick’s second law, taking into account an external mass transfer coefficient and the swelling of the solid matrix. Deff increased from 1.61 to 8.67 × 10−10 m2/s with moisture content, reached a threshold at moisture content 0.15 g/g d.b. and then decreased until water saturation. Deff decreased from 8.67 to 2.97 × 10−10 m2/s with decreasing porosity. This effect was attributed to a change of water diffusion mechanism, from predominant vapour to liquid. Deff decreased from 8.67 to 2.12 × 10−10 m2/s with increasing fat content. Addition of fat had an effect on the water diffusion in two ways, decreasing porosity (sagging of the foam) and increasing tortuosity.