Coagulation and proteolysis of high-protein milks in the gastric environment

Gastric digestion of 2 commercial ultrafiltered milks and milk enriched with skim milk powder (to simulate concentration by reverse osmosis) was investigated and compared with the digestion of nonconcentrated milk. Curd formation and proteolysis of high-protein milks in simulated gastric conditions were studied using oscillatory rheology, extrusion testing, and gel electrophoresis. The presence of pepsin in the gastric fluid triggered coagulation at pH >6 and the elastic modulus of gels from high-protein milks was similar to 5 times larger than the gel from reference milk. Despite similar protein concentrations, the coagulum from milk enriched with skim milk powder showed higher resistance to shear deformation than the coagula from ultrafiltered milks. The gel structure was also more heterogeneous. During digestion, the degradation of coagula from high-protein milks was slowed down compared with the coagulum from reference milk, and intact milk proteins were still detected after 120 min. Differences in the digestion patterns of coagula from high-protein milks were observed and were associated with the proportion of minerals bound to caseins and the denaturation rate of whey proteins.

Automated summary

This study investigated the gastric digestion of two commercial ultrafiltered milks and milk enriched with skim milk powder, and compared them with nonconcentrated milk. The results showed that the presence of pepsin triggered coagulation in the high-protein milks, and the gel formed was more elastic compared to the reference milk. The coagulum from milk enriched with skim milk powder showed higher resistance to shear deformation and a more heterogeneous gel structure. The digestion of coagula from high-protein milks was slower and intact milk proteins were still detected after 120 minutes.