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

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conference contribution
posted on 2023-10-27, 01:40 authored by Mengxiao Yang, Aiqian Ye, Zhi Yang, David Everett, Elliot Gilbert, Harjinder Singh

The structural properties of the pepsin-induced milk curd in the gastric environment could impact the emptying of the stomach contents and release of nutrients. Calcium is an important composition in milk. The effect of Ca2+ on pepsin-induced hydrolysis of κ-casein and subsequent coagulation of casein micelles was studied in a micellar casein solution at pH ~ 6.0 at 37 °C. An NaCl-supplemented micellar casein 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 the microstructure of curds induced by pepsin hydrolysis depended markedly on the addition of salts. Addition of CaCl2 up to 17.5 mM facilitated aggregation, with decreases in coagulation time and critical hydrolysis degree, and increases in firming rate and maximum storage modulus (Gʹmax); further addition of CaCl2 (22.5 mM) resulted in a lower Gʹmax. Increased ionic strength to 52.5 mM by adding NaCl retarded coagulation and resulted in a looser curd structure. In a human gastric simulator, micellar casein, 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 general hydrolysis of the caseins by pepsin. At the same CaCl2 concentration, a sample with higher ionic strength resulted in slower coagulation. This study provides further understanding on the effect of divalent (Ca2+) ions and ionic strength on the coagulation of casein micelles and the in vitro digestion behavior of milk.


MBIE Endeavour programme “Milks Mean More: Unlocking the potential of New Zealand's ruminant milks” 2018


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  • English

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AgResearch Ltd

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13th NIZO Dairy Conference

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Papendal, The Netherlands

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