The water activity, pH and other compositional parameters such as the moisture, fat and NaCl contents of various food emulsions were determined: butters, margarine (W/0) and mayonnaises (O/W). Water activity was determined by a gravimetric method (PEC procedure) and an instrumental method (dew-point hygrometer). The mean a(w) values obtained for the samples assayed were 0.904 +/- 0.050 (butters), 0.914 +/- 0.028 (margarines) and 0.947 +/- 0.013 (mayonnaises). The a(w) of the butter and margarine samples could be predicted with an error less than 0.02 units from the NaCl content of their aqueous phase (m) by using the following simple linear regression equation: a(w) = 0.954 - 0.036m. This equation could not be used to predict the a(w) of the mayonnaises, which, however, were obtained by using the Chen equation for mixtures of solutes.

The problem of the wall slip in steady-state flow measurements of oil-in-water (o/w) food emulsions has been investigated for different sensor system geometries and surface profiles. Experimental results demonstrated that slip effects are strongly dependent on the type of emulsion studied. This may be related to the emulsion microstructure. Thus, for instance, a highly structured gel-like continuous phase dampens wall slip effects, as opposed to emulsions in which creaming appears as a mechanism of instability, because of the formation of particulate flocs. The occurrence of wall slip is more clearly observed if the flow curves are obtained from stress sweep experiments. Although the recovery of the steady-state viscosity of a presheared sample is generally complete (similar values at low and high shear rates), the appearance of slip effects may be favoured by emulsion preshearing.

The viscous and viscoelastic behaviour of food emulsions containing a mixture of egg yolk and sucrose stearate as a function of oil and sucrose stearate concentrations were studied. Oil concentrations ranged between 40- 55% w/w for emulsions containing 5% w/w sucrose stearate and sucrose ester concentrations varied between 0-10% w/w for emulsions containing 50% w/w oil. steady flow, linear oscillatory shear tests and droplet size distribution measurements were carried out. An increase in oil or emulsifier concentration produced an increase in both the steady-state viscosity and in the viscoelastic functions. The results have been explained on the basis of the relationship between the structural parameters and the rheology of the emulsions studied.

Because many common foods are emulsions (mayonnaise, coffee creamers, salad dressing, etc.), a better understanding of lipid oxidation mechanisms in these systems is crucial for the formulation, production, and storage of the relevant consumer products. A research body has focused on the microstructural and oxidative stability of protein-stabilized oil-in-water emulsions that are structurally similar to innovative products that have been recently developed by the food industry (e.g., non-dairy creams, vegetable fat spreads, etc.) This review presents recent findings about the factors that determine the development of lipid oxidation in emulsions where proteins constitute the stabilizing interface. Emphasis is given to “endogenous” factors, such as those of compositional (e.g., protein/lipid phases, pH, presence of transition metals) or processing (e.g., temperature, droplet size) nature. Improved knowledge of the conditions that favor the oxidative protection of protein in emulsions can lead to their optimized use as food ingredients and thereby improve the organoleptic and nutritional value of the related products.