The structure of ovalbumin aggregates drives the proteolysis and pattern of peptide fractions generated during simulated digestion

Food structure can have a major impact on digestion in the gastrointestinal tract. Moreover, the structure of food proteins, which are typically consumed within complex food matrices, can be modified during food processing. Protein aggregation is one such modification and in the present study, the relationship between thermally-induced aggregated structures and in vitro digestion was explored using ovalbumin (the major egg white protein) as a food protein model. In order to explore the relationship between the structure of ovalbumin aggregates with their behavior during in vitro digestion, four different thermally-induced ovalbumin aggregates were prepared. The digestion of the latter aggregates and the resulting peptides profiles of the digests were investigated using an in vitro two-step model (stomach and small intestine mimicking the adult gastrointestinal tract). Different combinations of pH and ionic strength (IS; pH 5/IS 0.8M, pH 7/IS 0.3M, pH 7/IS 0.03M, pH 9/IS 0.03M) were used to generate different aggregate structures. These structures were characterized using light scattering methods, transmission electronic microscopy (TEM) and SDS-PAGE electrophoresis. Aggregate structures varied from random to linear, with particle size distributions (D[4;3]) ranging from 16nm to 90μm for linear and random aggregates, respectively. After in vitro simulated gastrointestinal tract digestion, the degree of hydrolysis of the linear aggregates was almost twice that of the random aggregates or the native ovalbumin. The overall peptide profiles of the digests of the untreated OVA and the random and linear OVA aggregate preparations were compared using spectral principal component analysis of reverse-phase HPLC chromatograms for each sample. Three distinct clusters were identified which corresponded to untreated OVA, linear aggregates and random aggregates treatments respectively. Consequently, based on an in vitro digestion model, it would appear that the type of protein aggregates present in a processed food may impact the extent and the nature of protein digestion in the gastrointestinal tract.