Issue 15, 2023

Role of Ca2+ in the pepsin-induced coagulation and in the dynamic in vitro gastric digestion behavior of casein micelles

Abstract

The effect of Ca2+ on pepsin-induced hydrolysis of κ-casein and subsequent coagulation of casein micelles was studied in a micellar casein (MC) solution at pH ≈ 6.0 at 37 °C without stirring. An NaCl-supplemented MC solution was used as a positive control to assess the effect of increased ionic strength after CaCl2 addition. Quantitative determination of the released para-κ-casein during the reaction using reverse-phase high-performance liquid chromatography showed that specific hydrolysis of κ-casein by pepsin was little affected by the addition of either CaCl2 or NaCl. However, rheological properties and microstructures of curds induced by pepsin hydrolysis depended markedly on the addition of salts. Addition of CaCl2 up to 17.5 mM facilitated coagulation, with decreases in coagulation time and critical hydrolysis degree, and increases in firming rate and maximum storage modulus (Gmax); further addition of CaCl2 (22.5 mM) resulted in a lower Gmax. Increased ionic strength to 52.5 mM by adding NaCl retarded the coagulation and resulted in a looser curd structure. In a human gastric simulator, MC, without the addition of CaCl2, did not coagulate until the pH decreased to ≈5.0 after ≈50 min of digestion. Addition of CaCl2 facilitated coagulation of casein micelles and resulted in more cohesive curds with dense structures during digestion, which slowed the emptying rate of caseins. At the same CaCl2 concentration, a sample with higher ionic strength coagulated more slowly. This study provides further understanding on the effect of divalent (Ca2+) ions and ionic strength on the coagulation of casein micelles and the digestion behavior of milk.

Graphical abstract: Role of Ca2+ in the pepsin-induced coagulation and in the dynamic in vitro gastric digestion behavior of casein micelles

Supplementary files

Article information

Article type
Paper
Submitted
22 Mar 2023
Accepted
04 Jul 2023
First published
05 Jul 2023

Food Funct., 2023,14, 6985-6997

Role of Ca2+ in the pepsin-induced coagulation and in the dynamic in vitro gastric digestion behavior of casein micelles

M. Yang, A. Ye, Z. Yang, D. W. Everett, E. P. Gilbert and H. Singh, Food Funct., 2023, 14, 6985 DOI: 10.1039/D3FO01126G

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