Competitive interfacial behavior in sodium caseinates-hydroxypropyl cellulose mixed systems

Abstract

In this work, interactions between hydroxypropyl cellulose (HPC) and sodium caseinates (Na-cas) at the air-water interface were studied. The surface tension, surface rheology, and film compatibility of the mixed protein/polysaccharide system were investigated. Tensiometry experiments showed that HPC is more surface-active than proteins, and is preferentially adsorbed at the interface. This molecule is able to migrate to the interface faster than Na-cas despite its larger size. At low HPC concentration, proteins adsorb first but HPC being more surface-active will eventually substitute them at the interface. The use of the pendant drop tensiometer allowed the real-time monitoring of protein displacement; an immediate decrease in surface tension was observed when HPC was added to a Na-cas solution. The analysis of the compression isotherms of Na-cas/HPC mixed films revealed partial miscibility between the two species within the monolayer; the films were less expanded than expected from the ideal behavior of binary mixtures. The dilatational rheology experiments showed that the presence of a very small amount of HPC had a significant effect on the viscoelastic properties of the interface. This work reported for the first time the competitive adsorption between Na-cas and HPC at the A/W interface.