Influence of calcium chelators on concentrated micellar casein solutions : from micellar structure to viscosity and heat stability

In practice it is challenging to prepare a concentrated medical product with high heat stability
and low viscosity. Calcium chelators are often added to dairy products to improve heat stability,
but this may increase viscosity through interactions with the casein proteins. The aim of this
thesis was to obtain a better understanding of the influence of different calcium chelators on the
physico-chemical properties of casein micelles and the resulting effect on viscosity and heat
stability of concentrated micellar casein isolate (MCI) solutions. The calcium chelators disodium
uridine monophosphate (Na2UMP), disodium hydrogen phosphate (Na2HPO4), trisodium citrate
(TSC), sodium phytate (SP), and sodium hexametaphosphate (SHMP) were studied.
Initially, the calcium-binding capacity of the phosphates was investigated and found to be
directly related to the amount of charges. The resulting effects on physical changes of casein
micelles were subsequently explored before and during heating. The viscosity of the MCI
solutions increased upon addition of the calcium chelators, which was attributed to swelling of
the caseins at decreasing calcium-ion activity. The calcium chelators induced different changes
in turbidity of the MCI solutions, which could be related to the degree of dissociation of the
casein micelles. Simulations of the ion equilibria indicated that the extent of casein micelle
dissociation followed the calcium-binding capacity of the calcium chelators. Micelle
dissociation occurred in the order of SHMP > SP > TSC > Na2HPO4 > Na2UMP. The results on
heat stability indicated that the calcium-ion activity and state of the micellar structure before and
during heating determined the heat stability of the MCI solutions. Na2UMP was the most
effective heat stabilizer, as it bound sufficient free calcium ions to reduce protein aggregation
without affecting the micellar structure. SHMP was the least effective heat stabilizer because of
heat-induced changes occurring during heating. For polyphosphates, SHMP and SP, it was
found that they decreased the isoint of casein by forming direct bindings with the caseins, for
which calcium ions were not required.
In conclusion, this thesis has provided new insights in the relationships between calcium
chelators and their influence on the casein micelle structure and on the physico-chemical
properties of concentrated MCI solutions. Also, the practical relevance for the dairy industry
was described, demonstrating how different calcium chelators can manipulate the viscosity and
heat stability of dairy products.