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.
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| Format: | Doctoral thesis biblioteca |
| Language: | English |
| Subjects: | calcium, casein, chelating agents, heat stability, micelles, milk products, viscosity, caseïne, chelaatvormers, hittebestendigheid, melkproducten, micellen, viscositeit, |
| Online Access: | https://research.wur.nl/en/publications/influence-of-calcium-chelators-on-concentrated-micellar-casein-so |
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| Summary: | 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. |
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