Foaming properties of protein/pectin electrostatic complexes and foam structure at the nanoscale

TL;DR

This study investigates how protein/pectin complexes influence foam stability and structure, revealing that complexes enhance foam stability without affecting film thickness, and clarifying the roles of free proteins and complexes in foam formation.

Contribution

It provides new insights into the effects of protein/pectin complexes on foam properties and introduces a novel in situ SANS method to measure foam film thickness.

Findings

Complexes improve foam stability but do not change film thickness.

Free proteins are essential for foam formation.

Complexes slow drainage, stabilizing foams.

Abstract

The foaming properties, foaming capacity and foam stability, of soluble complexes of pectin and a globular protein, napin, have been investigated with a "Foamscan" apparatus. Complementary, we also used SANS with a recent method consisting in an analogy between the SANS by foams and the neutron reflectivity of films to measure in situ film thickness of foams. The effect of ionic strength, of protein concentration and of charge density of the pectin has been analysed. Whereas the foam stability is improved for samples containing soluble complexes, no effect has been noticed on the foam film thickness, which is almost around 315 {\AA} whatever the samples. These results let us specify the role of each specie in the mixture: free proteins contribute to the foaming capacity, provided the initial free protein content in the bulk is sufficient to allow the foam formation, and soluble complexes slow down the drainage by their presence in the Plateau borders, which finally results in the stabilisation of foams.