HYGROMETRIC MEASUREMENTS FOR THE EVALUATION OF THE STABILITY OF MODELFOOD EMULSIONS

A non-destructive test is proposed, based on the measurement of the ch ange in the relative humidity (%RH) needed to reach the equilibrium va lue (%ERH), which makes a comparative evaluation of the degree of disp ersion between the aqueous and lipidic phase and the stability of emul sions. By measuring the rate to reach the %ERH, a kinetic index (k) ha s been introduced, describing the 'resistances' to the mass transport (water vapour) from the bulk emulsion to its surface and to the head s pace of the sample cell. To define this index a model of water adsorpt ion to the gas-liquid interface of the bulk emulsion is described. The model is based on a formalism similar to that used to describe a Lang murian kinetic. In oil-in-water emulsions the destabilising processes (creaming, coalescence) during storage are implied in the formation of a 'barrier' which block the aqueous vapour or decrease the rate at wh ich it comes to the surface. Thus, the corresponding k value of the mo del tends to decrease, and the decrease is higher for the more destabi lised emulsified system. In the water-in-oil dispersed systems, the k index is able only to describe the degree of dispersion and partly los es the ability to indicate changes that take place in the bulk system with time. (C) 1997 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd.