The Effect of Water and Fat Contents on the Enthalpy of Dissolution of Model Food Powders: A Thermodynamic Insight

The dissolution process of food powders is a topic of vast practical and commercial importance. However, the physical and chemical processes involved are far from being fully understood. Calorimetric determination of dissolution enthalpies ( ä H diss ) of food powders enables the extent of solute - solvent interactions to be assessed in terms of thermodynamic parameters. In this context, this work studied the effect of water and fat content representing typical food powders on the enthalpy of dissolution measured by isothermal calorimetry. The model food powders were obtained by freeze - drying a mixture of skim - milk powder, maltodextrin, and variable amounts of butter fat. The moisture content (MC) was determined gravimetrically, and the enthalpy of dissolution was measured by isothermal calorimetry at 30 ° C. The powders were studied in the dry state and after equilibration at different water activity (a w ) values. Near - infrared spectroscopy and X - ray powder diffraction data indicated that the powders were in an amorphous state after freeze - drying. Crystallization of lactose was observed after exposure of the powders to the higher a w investigated. The enthalpy of dissolution decreased (less exothermic) with increasing fat content in the dry samples (MC = 1% dry basis [db]), ranging from 62 to 34 J/g for powders containing 0.7 and 45% fat (wet basis [wb]), respectively. The MC also had a signifi cant effect on the enthalpy of dissolution. The exothermic enthalpy decreased from 62 to 5 J/g for powders containing 0.7% fat (wb) in the dry state (MC = 1.7% db) and after equilibration at 0.54 a w (MC = 11.4% db), respectively. A similar trend was observed for all other samples, for which the exothermic ä H diss of the equilibrated samples decreased with an increase in the MC.