Physicochemical characterization of hydroxypropyl methylcellulose based oil-in- water emulsions for edible film formation

Initial characteristics of emulsions would lead to different structures during drying of emulsion-based films, which in turn will affect the behavior of the film. The objective of this work was to study the effect of oil concentration and the use of surfactant over bubble sizes, interfacial tension, rheological properties and stability of oil-in-water emulsions stabilized by hydroxypropyl methylcellulose (HPMC) alone or by HPMC with sodium dodecyl sulfate (SDS). HPMC was used to prepare sunflower oil-in-water emulsions containing 0.3 or 1.0% (w/w) of oil, with or without SDS, using an ultrasonic homogenizer. Microstructure of emulsions was evaluated in terms of droplet sizes by means of image analysis. Interfacial tension measurements were carried out by the pendant drop method. Rheological properties were evaluated using the flow curve test. Stability of emulsions (creaming) was measured using a spectrophotometer at 850 nm. Image analysis did not show differences between droplet size distributions of emulsions prepared at different oil contents; however, by using SDS the droplet size distributions were shifted to lower values. Volume mean diameters were 3.79 and 3.77 μm for emulsions containing 0.3 and 1.0% without surfactant, respectively, and 2.72 and 2.71 μm for emulsions with SDS. Emulsions containing 0.3 and 1.0% oil showed a Newtonian behavior with viscosity values of 6.61×10 and 3.28×10 Pa s for emulsions formulated without surfactant and values of 6.23×10 and 5.60×10 Pa s when SDS was incorporated. Emulsions formulated with 1.0% of oil presented higher stability, with almost no change in normalized transmittance during 5 and 3 days of storage, for emulsions with and without SDS, respectively. Emulsions with an oil content of 0.3% showed an exponential decay of normalized transmittance with time. The oil content and the surfactant addition had an effect over the microstructure and physicochemical properties of HPMC-based emulsions which could lead to different microstructures during film formation.