Influence of pH on Heat-Induced Changes in Skim Milk Containing Various Levels of Micellar Calcium Phosphate
Elaheh Ahmadi | Todor Vasiljevic | Thom Huppertz
The present study investigated the effect of micellar calcium phosphate (MCP) content and pH of skim milk on heat-induced changes in skim milk. Four MCP-adjusted samples, ranging from 67 to 113% of the original MCP content, were heated (90 °:C for 10 min) at different pH values (6.3, 6.6, 6.9, and 7.2), followed by determining changes in particle size, turbidity, protein distribution, and structure. The results demonstrate a strong effect of MCP level and pH on heat-induced changes in milk, with the MCP67 samples revealing the greatest thermal stability. Specifically, decreasing MCP content by 33% (MCP67) led to a smaller increase in non-sedimentable &kappa:-casein and a lower decrease in &alpha:s2-casein concentrations after heating compared to other samples. Lower MCP content resulted in a moderate rise in the average particle size and turbidity, along with lower loading of &beta:-turn structural component after heating at low pH (pH 6.3). Notably, MCP113 exhibited instability upon heating, with increased particle size, turbidity, and a significant decrease in non-sedimentable &alpha:s2-casein concentration, along with a slight increase in non-sedimentable &kappa:-casein concentration. The FTIR results also revealed higher loading of intermolecular &beta:-sheet, &beta:-turn, and random coil structures, as well as lower loading of &alpha:-helix and &beta:-sheet structures in MCP-enhanced skim milk samples. This suggests significant changes in the secondary structure of milk protein and greater formation of larger aggregates.
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