How structure and assembly across different length scales influence protein digestion

Understanding how food structure impacts the availability of target molecules such as nutrients and bioactives during digestion is of crucial interest to strengthen the relationships between food and human health. This presentation gives an overview of the work conducted at INRA during the last 6 years on in vitro and in vivo digestion of milk and egg proteins. Our main objectives are to elucidate the mechanisms of protein structures disintegration in the GI tract and to determine if the laws driving native protein digestion can be applied to complex food matrices.At the molecular scale, the kinetics of native protein digestion are mainly driven by the 3D-structure of the biopolymer. Compact and globular proteins like β-lactoglobulin exhibit a high resistance towards the action of pepsin whereas the flexible caseins are rapidly hydrolysed. Local side chain dynamics may explain preferential cleavage of certain peptide bonds. At the supramolecular scale, linear fibril-like aggregates of ovalbumin are more prone to proteolysis than branched or spherical aggregates and the peptidome released in the small intestine is directly connected to the type of aggregate. At the micro/macroscopic scale, egg white gels made with linear aggregates form a dense network that seems to limit pepsin diffusion and increases resistance to in vitro digestion. In contrast, gels formed with large spherical aggregates exhibit spaced clusters surrounded by an aqueous phase that is favorable to pepsin diffusion increasing the susceptibility of these gels to digestion. Finally, complex dairy matrices of identical composition but different physical state (liquid, gel, solid) submitted to in vivo digestion in multi-canulated mini-pigs showed that the matrix structure affects the time of residence in the stomach and drives the kinetics of protein digestion and amino acids bioavailability in the bloodstream. The knowledge generated will help to design novel foods with controlled nutrient release.