Oat protein: Review of structure-function synergies with other plant proteins

Widespread adoption of plant-based alternatives over animal derived proteins provides a sustainable path to ensure food security for an increasingly growing population. Oat proteins, in particular, have generated noteworthy interests due to their high nutritional value, low environmental footprint and lack of allergenicity compared to other plant proteins. However, limited aqueous solubility at neutral pH can impair the techno-functional performance of oat proteins. Therefore, this review aims to provide a comprehensive understanding of structure-function relationships of oat proteins. In particular, we focus on current structural knowledge of the major oat protein fraction, 12S globulin, at three different length scales: (i) primary structure and amino acid composition, (ii) secondary structure and (iii) tertiary and quaternary protein structure. We then proceed to discuss (i) their properties in solution, i.e., solubility, surface hydrophobicity and surface charge in aqueous systems, (ii) their interfacial behaviour at air-water and oil-water interfaces, and (iii) their gelation and simple coacervation behaviour. We identify gaps in structural information and functional properties of oat proteins throughout and, where possible, complement these with parallel knowledge drawn from the cereal (rice) and legume family (pea, soy). Whilst oat proteins share stronger genetic similarities to rice based on amino acid sequence, their folded structure and overall functionality are surprisingly closer to legumes. Finally, we also emphasise the need for further structural and interfacial characterisation of oat proteins, in addition to an evaluation of their mouthfeel performance to increase their applications in sustainable plant protein-based food design.