Effect of oil content and surfactant addition on color and mechanical properties of hydroxypropyl methylcellulose emulsion-based edible films

The rearrangement of the oil droplets in the film matrix during film drying, which defines its internal and surface structure, has an important role in the optical and mechanical properties of the emulsion-based films. The objective of this work was to study the effect of oil concentration and the use of surfactant sodium dodecyl sulfate (SDS) over color and mechanical properties of hydroxypropyl methylcellulose (HPMC) emulsion-based edible films. HPMC was used to prepare sunflower oil-in-water emulsions containing 0.3 or 1.0% (w/w) of oil with or without SDS as surfactant. Emulsions were formed using an ultrasonic homogenizer. Edible films were obtained by drying the emulsions at 40 oC for 24 h and then equilibrate the films for 48 h at 22% HR. Transparency (T) of films was measured at a wavelength of 600 nm using a spectrophotometer. White index (WI) and total color change (∆E) of films were calculated from measurements done in L*a*b* scale by a colorimeter. Tensile measurements were carried out for films of 30 mm wide and 100 mm long. Tensile stress (σB) and percentage of elongation at break (EB) were calculated. The incorporation of oil produced a decrease in T and an increase in WI and ∆E of the emulsion-based films with respect to the pure HPMC film. The decrease in T and the increase in WI and ∆E were related to the light-scattering effect of oil, which was dependant of the microstructure of the emulsion-based films. Addition of oil and SDS decreased the σB of the emulsion-based films. The replace of HPMC by oil and SDS produce a lower “amount” of network structure in the films, leading to a weakening of their structure. The addition oil and SDS into edible films had no significant effect (p>0.05) over EB. Microstructure formation during drying of emulsion-based edible films had an enormous influence over the optical properties of films, transparency and color was dependant on the way that oil droplets were structured into the film.