Behaviour of potato protein-pectin conjugates in emulsions: Insights from interfacial shear rheology

Abstract

It is currently known that conjugation can improve the emulsion-stabilising properties of plant proteins, although the properties of conjugate samples at the oil/water interface are still unclear. This study characterises the interfacial rheological properties of potato protein-pectin conjugates, focusing on the impact of pH and pectin type. Potato protein was conjugated with low-methoxylated (LMP) and low-methoxylated amidated pectin (LMAP). Solubility, ζ-potential, denaturation temperature, and enthalpy were determined to characterise the effect of the conjugation. Interfacial film formation and viscoelastic properties of the interfacial films of the conjugate samples were evaluated using interfacial shear rheology. Previous studies demonstrated that conjugates can produce stable emulsions. This study further examines oil/water interface stabilisation at pH 3 and pH 6 - the isoelectric point of conjugates and potato protein - where the opposite polymer consistently exhibited superior functional properties. During conjugation, the protein remains undenatured, allowing it to form a viscoelastic film at the interface. Conjugates form these films faster than protein alone but exhibit stronger plastic behaviour with increasing mechanical deformation. At pH 3, conjugated LMP forms a compact, dense boundary layer over the loose protein interfacial film. In contrast, conjugated LMAP forms a loose boundary layer that retains structural integrity longer with increasing shear deformation. At pH 6, both conjugates behave similarly, with increased pectin chain repulsion preventing the formation of a boundary layer around the dense protein interfacial film. This study demonstrates that pH and pectin type significantly influence the stabilising behaviour of potato protein-pectin conjugates, offering insights into their potential for tailored emulsion applications. • Protein and conjugated protein form viscoelastic network structures at the o/w interface. • Use of conjugates provides an additional pectin boundary layer at the interface. • pH affects protein film formation at the o/w interface, affecting density and mechanical resistance. • Pectin controls boundary layer density and thickness, causing pH-dependent variations in the film's mechanical stability. • Differences in interfacial properties stem from variations in polymer charge.

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