Hygrometric measurements for the evaluation of the stability of model food emulsions
1997
Pittia, P. | Gambi, A. | Lerici, C.R.
A non-destructive test is proposed, based on the measurement of the change in the relative humidity (%RH) needed to reach the equilibrium value (%ERH), which makes a comparative evaluation of the degree of dispersion between the aqueous and lipidic phase and the stability of emulsions. By measuring the rate to reach the %ERH, a kinetic index (k) has been introduced, describing the 'resistances' to the mass transport (water vapour) from the bulk emulsion to its surface and to the head space of the sample cell. To define this index a model of water adsorption to the gas-liquid interface or the bulk emulsion is described. The model is based on a formalism similar to that used to describe a Langmurian 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 which it comes to the surface. Thus, the corresponding k value of the model tends to decrease, and the decrease is higher for the more destabilised emulsified system. In the water-in-oil dispersed systems, the k index is able only to describe the degree of dispersion and partly loses the ability to indicate changes that take place in the bulk system with time.
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