Influence of pH and pectin type on properties and stability of sodium-caseinate stabilized oil-in-water emulsions

The influence of pH and pectin type on the stability and properties of sodium caseinate stabilized oil-in-water emulsions was assessed by measuring ζ-potential, particle size, microstructure, apparent viscosity, and creaming stability. Emulsions containing droplets stabilized by sodium caseinate (CAS) were prepared by homogenizing 10 wt% corn oil with 90 wt% aqueous CAS solution (1.0 wt%, pH 7.0). High methoxyl pectin (59% DE) or low methoxyl pectin (32% DE) were then added to the emulsions and the final pH was adjusted (pH 3–7). In the absence of pectin, the CAS emulsions were unstable to droplet flocculation and coalescence over the range 3≤pH≤5 which was attributed to their relatively low droplet charge. ζ-potential measurements indicated that both types of pectin adsorbed to the droplet surfaces at pH 3–5, but not at pH 6 and 7, which was attributed to electrostatic attraction between anionic groups on the pectin and cationic groups on the CAS. Irreversible droplet aggregation was observed at pH 3 and 4 due to charge neutralization and bridging flocculation by the pectin molecules, whereas reversible droplet aggregation was observed at pH 6 and 7, which was attributed to depletion flocculation by non-adsorbed pectin. The stability of the CAS emulsions to droplet aggregation was improved by pectin at pH 5, which was attributed to multilayer formation. There was little influence of the degree of esterification (DE) of the pectin molecules on CAS emulsion stability at any pH.