A Study of the Rheology of Low-in-Fat O/W Emulsions with Emphasis in Flow Behavior Modeling

LORENZO G.,; ZARITZKY N.; CALIFANO A.

Napoles, Italia

Simposio; Third International Symposium on FOOD AND AGRICULTURAL PRODUCTS: PROCESSING AND INNOVATIONS; 2007

International Commission of Agricultural Engeenering, CIGR

The incorporation of hydrocolloids is a suitable alternative to stabilize low-in-fat O/W emulsions against creaming. However gum concentration as well as their structural features must be carefully selected in order to obtain a stable product with appropriate viscoelastic behavior. In this work the effect of composition on rheological properties and stability of low-in-fat O/W emulsions was studied. Continuous phase was formulated using xanthan/guar gum mixtures in an acidic aqueous solution with 2% ClNa. Polyoxyethylene-sorbitan-monooleate (TweenÒ 80) was used as emulsifier and sunflower oil as the disperse phase. A central composite design involving oil fraction and gum content was used. Linear viscoelastic behavior (storage(G’) and loss(G’’) moduli vs. frequency) and steady flow curves were obtained for both emulsions and continuous phases. Droplet size distribution was measured by light scattering and complemented with microscopic observations. In all cases Sauter diameter values between 1.7-1.8μm were obtained. Micrographs revealed a flocculated system. Frequency sweeps showed that both G’ and G’’ increased with oil content. However, the viscoelastic behavior was mainly governed by the hydrocolloid content. At 1.25% or over, a weak gel structural network was observed (G’>G’’) due to droplet flocculation. Below 1.25%, the viscoelastic behavior corresponded to polymeric dispersion where G’ y G’’ curves intersected within the range of tested frequencies. Both aqueous dispersions and emulsions showed a shear-thinning behavior, which was successfully modeled with Ellis equation. Mooney equation, which relates relative viscosity with oil fraction, was used to obtain the shape factor and maximum packaging volume fraction. Zero shear viscosity was also predicted based on emulsion composition by response surface methodology. Visual inspections of the formulated emulsions showed that they remained stable after eight months and were adequate to be used as pourable dressings.