Heating and glycation of β-lactoglobulin and β-casein: Aggregation and in vitro digestion

Heat treatment is commonly used in dairy technology. Usually, milk is heated and cooled many times before to obtain the final product and milk components are then subject to cumulative heat treatments. In the present work, we investigated the heat induced aggregation (90 °C until 24 h) of two model proteins, β-lactoglobulin (β-Lg) and β-casein (β-CN), in the presence of glucose and subsequent consequences on simulated gastro-duodenal digestion. Protein aggregation and digestion were monitored using polyacrylamide gel electrophoresis, size exclusion chromatography, dynamic light scattering and transmission electron microscopy. Concomitant heating and protein glycation affect aggregation kinetics as well as protein sensitivity to enzymatic digestion. Spherical covalently linked aggregates were favored in the case of β-CN in the presence of glucose. Glucose limited the formation of twisted fibrils from β-Lg. We clearly showed that aggregates of both proteins formed in the presence of glucose were more resistant to enzymatic digestion. Those formed from β-Lg being highly resistant and still present at the end of simulated gastro-duodenal process. These findings underline the importance not only of the aggregation as such but also of the nature of formed aggregates on protein digestibility.