Self-assembly of rice proteins: A perspective on elevating rice protein techno-functional properties

The worldwide demand for plant protein has increased in recent years. Rice and its by-products are potential sustainable, economical, and high-quality protein sources. Rice protein exhibits a balanced amino acid composition and hypoallergenic properties, and has been utilized as a commercial food ingredient. However, rice glutelin (RG), the main component of rice protein, is prone to aggregate under food processing conditions, resulting in large-size aggregates, which in turn result in low water solubility that limits its functional properties. This review clarifies the rules governing the low solubility of RG, discusses the research progress on its self-assembly behavior, and summarizes effective methods to improve its techno-functional properties. The aggregation of RG under neutral conditions is due to an uneven charge distribution, high hydrophobicity, and disulfide bond cross-linking of amino acids in the protein molecules. RG possess promising tunable self-assembly behaviors, which can occur in RG itself or with other molecules (polysaccharides and phenolic compounds). Various structures such as nanofibrils, nanoparticles, complexes, and conjugates were formed by controlling different factors, including the processing environment (pH, temperature, and ionic strength) or the addition of polymers (type or mixture ratio). Finally, tailored functionalities (solubility, foaming, emulsifying, and gelling properties) of self-assembled RG were summarized. In the future, self-assembling RG can be promoted as an advanced functional ingredient for commercial food applications, such as emulsions, delivery systems, functional foods, and sustained release of active food additives.