Moisture sorption characteristics of heat treated flour, culinary flour and high ratio cake

The quality of preserved food is largely dependent on its moisture content, moisture migration and/or moisture uptake of the food during storage. Therefore, the water activity level, which corresponds to a range of equilibrium moisture contents, must be determined by, for example, the use of moisture isotherms. The shape of the isotherm curve is dependent on the interactions between the vapour molecules and the solid material which can aid understanding of the mechanism taking place during water sorption. The moisture sorption isotherms of heat treated flour, culinary flour and convective oven baked Madeira (high ratio) cake were experimentally determined using a standard gravimetric method. Experimental data was compared with traditional mathematical models and their goodness of fit evaluated. The isotherms showed that heat treated and culinary flours exhibited Type II characteristics with cake showing Type III, due to its higher sugar content. Ferro-Fontan, GAB and Peleg models all adequately represented the results.