Effects of thermal, non-thermal and emulsification processes on the gastrointestinal digestibility of egg white proteins

Background: Egg white proteins (EWPs) are an excellent source of essential amino acids for human nutrition. Also, egg white is commonly used in food processing because of its numerous technological functionalities. Processing can influence the EWPs digestibility and thereby amino acid bioavailability. A better understanding of processing effects on EWPs digestibility enables improving the nutritional value of EWP products. Scope and approach: This review elucidates the impact of diverse processing methods on EWPs at molecular level (individual molecules), supramolecular level (aggregated state), and macroscopic level (gelled state). Key findings and conclusions: Heat, high pressure, ultrasound, pulsed electric fields, and adsorption at interface can unfold native EWPs, causing exposure of hydrolysis sites and improvement of protein digestibility at molecular level. However, the Maillard glycation of EWPs may restrict the access of digestive enzymes to the proteins and reduce their digestibility. The Maillard reaction can also lower the IgE-binding capacity of ovalbumin, which could potentially reduce allergenicity. At supramolecular level, protein-protein interactions between the unfolded EWPs lead to the formation of aggregates with different morphologies, depending on the pH and ionic strength. The accessibility of digestive enzymes to the cleavage sites of heat-induced spherical aggregates is lower compared to the linear counterparts. However, gels formed from the linear aggregates show high resistance to digestion owing to the dense network of these gels. A combination of processes can increase the impact of digestibility. For instance, quick production of specific bioactive peptides can be achieved by applying enzymatic treatment to EWPs under high pressure.