Impact of total calcium in milk protein concentrate on its interaction with the aqueous phase

The impact of calcium level in milk protein concentrate (MPC80) containing 80% protein on its interaction with the aqueous phase was investigated. Partial acidification (pH 6.0) together with cation exchange processing was employed to modify the mineral content of control MPC (CMPC, having 2.87% (w/w) calcium) to yield MPCs with medium (1.57% w/w), low (1.00% w/w) and very low (0.36% w/w) calcium contents, namely MPCF1, MPCF2 and MPCF3, respectively. The total protein contents of CMPC, MPCF1, MPCF2 and MPCF3 was 85.58, 82.01, 81.27 and 79.50 (%, w/w), respectively, while their undenatured whey protein (WP) contents were 6.03, 4.97, 4.62 and 3.51 g/100 g overall protein, respectively. The mineral profiles on the powder particle surfaces of the different MPCs was determined using X-ray photoelectron spectroscopy (XPS). The surface calcium and sodium contents of CMPC and MPCF3 were 0.3% and 0.0%, and 0.2% and 0.4% atomic concentration, respectively. Technofunctional property analysis showed that MPCF2 had the highest water holding capacity (3.40 g water/g protein) among the calcium reduced MPCs. The overall solubility following centrifugation of 5% (w/v, on a protein basis) aqueous reconstituted CMPC (65.82%), MPCF1 (76%), MPCF2 (83%) and MPCF3 (97%) was determined. Furthermore, nitrogen solubility for 4% (w/v, on a protein basis) aqueous suspensions at pH 4.0, 7.0 and 10.0 showed that all samples had low solubility at pH 4.0 ranging from 10% to 22%. Complete solubility was observed at pH 7.0 for MPCF2 and MPCF3 while the solubility of MPCF1 and CMPC at this pH was 77% and 85%, respectively. Complete solubility of all MPC80 samples was observed at pH 10. In conclusion, partial acidification followed by cation exchange chromatography led to the production of MPC80s with different calcium levels. These MPC80 ingredients displayed different powder particle surface compositions and had different interactions with the aqueous phase. Targeted modification of mineral/calcium content may be employed to generate MPC ingredients with different surface properties and functionalities.