Stability of rice bran oil-in-water emulsions stabilized by pectin–zein complexes: Effect of composition and order of mixing

Abstract

Polysaccharide−protein complexes can be used to improve the physical stability of oil-in-water emulsions. The purpose of this study was to investigate the effects of concentration of citrus pectin, zein and oil as well as order of mixing on physical properties and stability of emulsions stabilized by pectin–zein complexes. Emulsions containing oil phase (5–30% w/w rice bran oil) and aqueous phase (0.5–2% w/w pectin, adjusted to pH 4) were prepared by mechanical homogenizer. The zein concentration (0.001–0.5% w/w) was added in either primary or secondary emulsification step. The obtained emulsions were then assessed by measuring droplet size, zeta potential, microstructure, apparent viscosity, and emulsion stability after storage at ambient temperature and under environmental stress conditions. Using 1.5% w/w pectin could produce the stable emulsions with low percent creaming index, at the oil concentration of 15 and 20% w/w. Moreover, the stable emulsions could be formed when the zein was added after pectin adsorption (secondary emulsification) but not when it was added together with pectin. This was attributed to electrostatic attraction between cationic groups on zein molecules and anionic groups of pectin on the droplet surface. We also found that pectin−zein stabilized emulsions were much more stable than emulsions stabilized by pectin or zein alone. The stability of emulsions also increased as zein concentration was increased. The results suggested that the pectin–zein complexes could be used to improve the physical stability of oil-in-water emulsions, especially the formulations with a high volume fraction of oil.