Sodium caseinate hinders chymosin-induced aggregation of caseins in concentrated milk: The role of soluble caseins and calcium ions

P Krishnankutty Nair,M Corredig

doi:10.3168/jdsc.2021-0124

Abstract

Concentrated casein micelle suspensions show an altered balance between the colloidal and soluble phases compared with native skim milk. The objective of this research was to probe the role of such a change on the chymosin-driven destabilization of casein micelles. Skim milk was gently concentrated by osmotic stressing to increase the volume fraction of the micelles while maintaining a constant ionic composition. In situ turbidity measurements demonstrated that the secondary stage of gelation was hindered in the concentrated suspensions. Addition of ionic calcium overcame this inhibition, whereas restoring the original concentration by redilution did not. This work clearly demonstrated that calcium plays a major role in decreasing electrostatic repulsion in casein micelles, but also showed the importance of noncolloidal proteins in altering the gelling functionality of casein micelles in concentrated milk. Additional calcium induces aggregation of these soluble caseins, restoring gelation in concentrates.

Highlights

Concentrated casein micelle suspensions show an altered balance between the colloidal and soluble phases compared with native skim milk
In skim milk, when more than 90% of κ-casein is hydrolyzed (Dalgleish, 1992), the micelles aggregate if sufficient calcium ions are present (Lucey, 2009)
If additional calcium is added to skim milk, coagulation of casein micelles starts earlier than the 90% threshold (Sandra et al, 2012) because of a reduction in electrostatic repulsion forces

Summary

Introduction

Abstract: Concentrated casein micelle suspensions show an altered balance between the colloidal and soluble phases compared with native skim milk. Additional calcium induces aggregation of these soluble caseins, restoring gelation in concentrates. In skim milk, when more than 90% of κ-casein is hydrolyzed (Dalgleish, 1992), the micelles aggregate if sufficient calcium ions are present (Lucey, 2009).

Objectives

Results

Conclusion