Effect of low-methoxy pectin on interfacial and emulsion stabilizing properties of heated whey protein isolate (WPI) aggregates

Abstract

• QCM-D study of heated WPI and heated biopolymer complexes on hydrophobic surface. • A higher ratio of pectin to WPI increased the adsorbed mass on the surface. • A higher ratio of pectin to WPI decreased the protein load from 15.11 to 9.19 mg/m 2 . • Interfacial properties of the heated WPI-LMP affected the emulsion stability. In this study, we have investigated the interfacial and emulsion stabilizing properties of heat-induced whey protein isolate (WPI) aggregates prepared in the presence or absence of low-methoxy pectin (LMP). Sub-micron complex particles were formed by heating of oppositely charged WPI and LMP at different WPI:LMP mass ratios. The Quartz Crystal Microbalance with Dissipation (QCM-D) technique was used to better understand the adsorption properties of these biopolymeric particles at a model hydrophobic surface. Clear correlations were observed between the interfacial properties of WPI and WPI:LMP aggregates and the resulting emulsion characteristics. Compared to WPI aggregates (which led to emulsions containing larger flocculated droplets), the heated complexes (formed at a higher ratio of LMP to WPI) were highly efficient as Pickering stabilizers leading to emulsions with smaller droplets (5.5–6.8 μm). Cryo-SEM analysis clearly revealed the manipulation of the emulsions’ interfacial microstructure due to the adsorption of a WPI:LMP inter-polymeric film onto the surface of the droplets. The effectiveness of the colloidal particles in stabilizing emulsions depended largely on the formation of a sufficiently ‘dense layer’ of particles at the oil-water interface where these properties were controlled by the composition of WPI and LMP at the oil droplet surface. Moreover, the emulsion physical stability was greatly influenced by the formation of an inter-connected film at the oil droplet interface, whereby these viscoelastic films increased the steric hindrance against coalescence of emulsion droplets. This work provides the mechanism of emulsion stabilization by WPI particles formed by heating in the absence or presence of pectin.