Relating the structural, air-water interfacial and foaming properties of wheat (Triticum aestivum L.) gliadin and maize (Zea mays L.) zein based nanoparticle suspensions

Protein based nanoparticles (NPs) are promising new surface-active ingredients for stabilizing air-in-water or oil-in-water dispersions in food systems. Fundamental knowledge on their structure-function relationship is still lacking. Here, NPs based on wheat gliadins (WGNPs) and maize zeins (MZNPs) were produced using liquid anti-solvent precipitation. MZNPs had much higher surface hydrophobicity (SH) than WGNPs. Defatting of gliadin and zein powders prior to NP production revealed that their endogenous lipids do not impact neither size, surface charge and SH of WGNPs or MZNPs. Thus, the high SH of MZNP could be ascribed solely to its proteins. WGNPs had excellent foaming capacity and foam stability, while foam could barely be formed from MZNPs. The foaming properties of mixed gliadin-zein particles of intermediate SH were worse than expected based on their gliadin contents. The presence of zein in nanoparticles thus resulted in poor foam stability. Interestingly, all foaming characteristics could be related to the build-up of a viscoelastic interfacial protein film upon NP adsorption. Indeed, WGNP had much higher surface dilatational moduli than MZNPs, which was in line with the former’s superior foaming properties. This suggests that for WGNPs and MZNPs to efficiently stabilize interfaces, they need to partially disintegrate and spread at the interface, thereby mutually interacting and forming a coherent viscoelastic protein film.