Impacts of N-(n-Butyl)thiophosphoric triamide (NBPT) on the physicochemical properties of milk protein isolate (MPI) dispersions: A study on micelle integrity

This study investigated the effects of the urease inhibitor N-(n-Butyl)thiophosphoric triamide (NBPT) on milk protein isolate (MPI) dispersions. The addition of NBPT to MPI led to significant (p < 0.05) reductions in particle size (from 154 to 119 nm) and significant (p < 0.05) increases in sample polydispersity index for the MPI control and MPI containing 3 mg/mL NBPT respectively, which is suggestive of micelle dissociation presumably due to the release of calcium sensitive caseins and the subsequent generation of small protein aggregates. Zeta potential values of MPI became more negative and increased from −26.4 in the MPI control to −44.7 Mv in the presence of 3 mg/mL NBPT. Increased calcium (Ca^{2 +}) ions in the serum phase of MPI containing NBPT delayed rennet gelation due to slower hydrolysis of kappa-casein, these gels also exhibited increased strength which could be attributed to enhanced Ca²⁺ crosslinking. Acid-induced MPI-NBPT gels displayed delays in gelation time due to altered buffering capacities. NBPT caused significant (p < 0.05) decreases in final surface tension values. NBPT marginally increased the heat stability of MPI. Overall, NBPT significantly impacted the structural and functional properties of MPI dispersions due to the displacement of Ca²⁺ from phosphoserine (SEP) residues in colloidal calcium phosphate (CCP).