Influence of calcium chelation and enzymatic modification of protein on the hydration characteristics of high protein dairy powders
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Date
2020-06
Authors
Power, Orla M.
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Publisher
University College Cork
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Abstract
Milk protein concentrate (MPC) powders have numerous commercial applications and are integral ingredients in high quality functional dairy products and beverages. However, such high protein dairy powders pose significant technical challenges during processing and rehydration, due to high viscosity and poor powder particle dissolution, respectively. Previous work has shown that the use of calcium chelating salts is effective in improving dissolution of MPC powders; however, the use of such salts results in considerable increases in viscosity and reduction in casein micelle integrity. The objective of this research was to investigate the impact of depleting calcium in micellar casein systems after either enzymatic dephosphorylation or enzymatic crosslinking and to examine viscosity, particle size; ζ-potential and colour of the protein solutions and subsequent rehydration properties of these spray dried systems. Calcium depletion was achieved through either addition of a chelating salt (sodium hexametaphosphate; SHMP) or through ion exchange.
MPC dispersions containing enzymatically dephosphorylated casein proteins exhibited lower viscosity than phosphorylated MPC dispersions; however, the former resulted in a loss of casein micelle integrity in the presence of SHMP. Phosphate nuclear magnetic resonance spectroscopy proved useful for quantifying the depletion of calcium phosphate from casein micelles and confirmed dephosphorylation. Enzymatic crosslinking of casein proteins using transglutaminase helped maintain a lower solution viscosity after calcium chelation by SHMP, and the resultant dispersions retained a higher degree of casein micelle integrity compared to non-crosslinked MPC dispersions. Co-dried crosslinked casein and SHMP powders had improved rehydration properties. As an alternative to the addition of calcium chelating salts, a strong cation exchange resin was investigated for its ability to deplete calcium to varying extents in the production of novel MPC powders with improved dissolution properties at low levels of calcium depletion. However, similar to with direct use of calcium chelating salts, concomitant increases in viscosity and decreases in micelle integrity were observed in MPC dispersions, with the effects increasing with extent of calcium removal. Solubility and dissolution properties of calcium depleted MPC powders exhibited improved rehydration ability and caused a shift in their heat stability towards lower pH values. MPC dispersions containing crosslinked proteins were observed to be more resistant to calcium depletion compared to their respective control samples. MPC dispersions containing crosslinked MPC proteins retained greater micelle integrity; however, extensive calcium reduction resulted in significantly higher viscosity than corresponding controls.
This thesis provides new insights into the functionality of novel MPC powders generated using enzymatic modification of casein and chemical modification of the calcium content and distribution between colloidal and serum phases, resulting in MPC powders with enhanced functionality. The outcomes of this research have application in the formulation of MPC powders with improved dissolution properties and reduced viscosity.
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Keywords
Milk protein concentrate , Enzymes , Calcium chelating , Transglutaminase , Dephosphorylation , Viscosity , Rehydration , Calcium ion exchange , Dissolution , Milk protein powders , Spray drying
Citation
Power, O. M. 2020. Influence of calcium chelation and enzymatic modification of protein on the hydration characteristics of high protein dairy powders. PhD Thesis, University College Cork.