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Effect of soluble casein isolate on the functionality and mechanical properties of milk protein concentrate (MPC80) during storage.

Y. Zhu

Abstract:

M10
Effect of soluble casein isolate on the functionality and mechanical properties of milk protein concentrate (MPC80) during storage.
Y. Zhu*1, M. S. Molitor2, S. Ikeda1, J. A. Lucey2. 1Department of Food Science, University of Wisconsin-Madison Madison, WI, 2Center for Dairy Research, University of Wisconsin-Madison Madison, WI.

MPC80 is a high-protein milk powder widely used in the food industry as a functional ingredient. A problem associated with MPC80 is its poor solubility, which can further deteriorate during storage at high temperature and humidity. A new approach to improve MPC solubility was investigated. The Center for Dairy Research (CDR) has developed a technology to produce soluble casein isolate (SCI), which is very similar to sodium caseinate but made via a membrane filtration method. Various levels (0, 1, 5, 10%) of soluble casein isolate (SCI), manufactured by CDR, was added to the UF retentate before spray drying and the MPC powders were stored at 30�C for up to 60 d after manufacture. The above processes were replicated twice, using different lots of skim milk. The results showed that addition of SCI did not change the particle size distribution or disrupt the casein micelle structure. Adding 5% or more SCI (in final dry matter) significantly improved MPC solubility and foam capacity on d 0 (P < 0.05), but the foam capacity was not significantly different after 60 d storage (P > 0.05). Atomic force microscopy (AFM) operated in Peak Force QNM mode was used to investigate the nanomechanical properties of powder particle surfaces. The powder particle surface topography was hardly impacted by storage under high temperature, however, storage under high temperature led to an increase in powder stiffness for all 4 samples and the elastic modulus of the MPC samples was negatively correlated with solubility (r = −0.86, P < 0.001). Addition of SCI, at levels 5—10% in final dry matter, could have increased the amount of non-micellar casein on powder surface and possibly slow down the case hardening of MPC powder particles during high temperature storage, which might have contributed to the improvement in solubility and functionality.

Keywords: milk protein concentrate, soluble casein isolate, atomic force microscopy Peak-force QNM.