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Kinetics of pepsin-induced hydrolysis and the coagulation of milk proteins

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posted on 2023-05-03, 20:02 authored by Mengxiao Yang, Aiqian Ye, Zhi Yang, David Everett, Elliot Gilbert, Harjinder Singh
Hydrolysis-induced coagulation of casein micelles by pepsin occurs during the digestion of milk. In this study, the effect of pH (6.7–5.3) and pepsin concentration (0.110–2.75 U/mL) on the hydrolysis of κ-casein and the coagulation of the casein micelles in bovine skim milk was investigated at 37°C using reverse-phase HPLC, oscillatory rheology, and confocal laser scanning microscopy. The hydrolysis of κ-casein followed a combined kinetic model of first-order hydrolysis and putative pepsin denaturation. The hydrolysis rate increased with increasing pepsin concentration at a given pH, was pH dependent, and reached a maximum at pH ∼6.0. Both the increase in pepsin concentration and decrease in pH resulted in a shorter coagulation time. The extent of κ-casein hydrolysis required for coagulation was independent of the pepsin concentration at a given pH and, because of the lower electrostatic repulsion between para-casein micelles at lower pH, decreased markedly from ∼73% to ∼33% when pH decreased from 6.3 to 5.3. In addition, the rheological properties and the microstructures of the coagulum were markedly affected by the pH and the pepsin concentration. The knowledge obtained from this study provides further understanding on the mechanism of milk coagulation, occurring at the initial stage of transiting into gastric conditions with high pH and low pepsin concentration.


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© 2022, The Authors. Published by Elsevier Inc. and Fass Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (


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Journal title

Journal of Dairy Science




Yang, M., Ye, A., Yang, Z., Everett, D. W., Gilbert, E. P., & Singh, H. (2022). Kinetics of pepsin-induced hydrolysis and the coagulation of milk proteins. Journal of Dairy Science, 105(2), 990–1003.

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