Physicochemical stability of citral emulsions stabilized by milk proteins (lactoferrin, α-lactalbumin, β-lactoglobulin) and beet pectin

Citral emulsions were prepared by the layer-by-layer deposition technique based on the electrostatic interaction between positively charged milk proteins (lactoferrin, α-lactalbumin or β-lactoglobulin, at pH 3.5) and a negatively charged polysaccharide (beet pectin), which had different interfacial compositions: (i) primary emulsions (milk proteins); (ii) secondary emulsions (milk protein-beet pectin). The effects of environmental stresses (ionic strength, pH, thermal treatment) on the physicochemical stability of citral emulsions were investigated. In the absence of beet pectin, citral emulsions were highly unstable and aggregated at pH close to the pI of the proteins and NaCl concentration of 0.1–0.5 M. The droplets in milk protein-beet pectin coated emulsions were stable against the aggregation at pH range of 3.5–10 and NaCl concentration of 0.1–0.5 M. During the storage of 4 weeks, secondary emulsions exhibited better physical stability than primary ones and could protect the isomers (neral and geranial) of citral from degradation at 25 °C. In general, lactoferrinn-beet pectin stabilized emulsion exhibited the best physicochemical properties among emulsions involved in this study.