Relating the foaming properties of oat proteins to their air-water interfacial characteristics and thin film drainage dynamics

Abstract

Oats have emerged as a promising raw material for liquid and semi-solid foods due to their balanced amino acid profile and high globulin content. Food foam-type products, such as meringue, whippable drinks, and ice cream, rely heavily on protein functionality. Understanding the mechanisms by which oat proteins form and stabilize foam is crucial for their application in such products. This study relates the foaming properties of non-kilned oat protein fractions enriched in either water-soluble proteins or unaggregated 12S globulins to their behavior at air-water interfaces (using maximum bubble pressure and (oscillating) rising bubble tensiometry) and during the drainage of thin liquid films (using a pressure-controlled microfluidic set-up). Both water-soluble oat proteins and 12S globulins were capable of producing a high volume of stable foam. The foaming capacity of the water-soluble oat proteins was attributed to their high diffusion rate to the air-water interface, while their foam stability was ascribed to the rapid formation of a viscoelastic interfacial film. The foaming capacity of oat 12S globulins was driven by extensive protein structural reorganization upon adsorption, likely involving dissociation and reassociation of oligomers and protein subunits, after surpassing an energy barrier-controlled adsorption regime at very low surface ages. The stability of oat 12S globulin foams was attributed to enhanced thin liquid film stability, resulting from reduced Laplace pressure gradients, and increased disjoining pressure due to combined electrostatic and steric repulsion. This study provides novel mechanistic insights into the foaming properties of oat proteins, paving the way for their utilization in plant-based foods.