Formation of non-enzymatic protein modifications (nePTMs) on caseins and whey proteins during dry heating and the impact on their in vitro infant digestion profile

Thermal treatment during infant formula processing results in the generation of various non-enzymatic protein modifications (nePTMs). In this study, dry heating of a casein or whey protein model system was used to investigate the formation of protein-bound nePTMs after heating from 0 to 72 h. Oxidation, lactosylation, carboxymethylation, 3-deoxyglucosone and hexose modification were the predominant nePTMs, which were found to be protein- and site-specific. Lower solubility of glycated caseins resulted in lower in vitro digestibility in the gastric phase compared to glycated whey protein. After intestinal digestion, the level of carboxymethylation and furosine in the soluble phase increased, especially for 72 h glycated casein, which also showed the highest soluble nitrogen level. This study illustrated that the formation of thermal-induced nePTMs of caseins and whey proteins were heating time dependent and linked to digestion efficiency, thus providing novel insights to further understand the effect of nePTMs on proteins' digestion profiles.