80-2 |
Structural properties of casein micelles in high pressure-treated milk |
A. L. KELLY1, T. Huppertz2, and P. F. Fox2. (1) Dept. of Food Science & Technology, Univ. College Cork, Cork, Ireland, (2) Dept. of Food Science, Food Technology & Nutrition, Univ. College Cork, Cork, Ireland High pressure (HP) processing affects many constituents of milk, including whey proteins, casein micelles and enzymes, as well as the mineral balance. In this study, the effects of HP on casein micelles in milk were investigated, to underpin understanding of the effects of this technology on the properties of milk and dairy products. Treatment for 30 min at <200 MPa had little effect on casein micelle size, measured by photon correlation spectroscopy, whereas size increased following treatment at 250 MPa and decreased considerably at 300-800 MPa. Treatment for up to 10 min at 250 MPa decreased micelle size, but longer treatment times (up to 60 min) increased this parameter. Reductions in micelle size observed at 400 MPa were independent of treatment time (2-30 min). Both elevated milk pH (adjustment to pH 7.0) and higher treatment temperature led to greater micelle sizes after HP treatment, whereas reducing pH (to 6.2) or temperature had the opposite effect. After HP treatment, micelle size in serum protein-free skim milk was considerably smaller than in raw skim milk, indicating a key role of whey proteins in effects observed, while casein particles in CCP-free milk were not disrupted by HP treatment. Casein micelles in HP-treated milk were disrupted further by addition of tri-sodium citrate or urea, indicating that at least some CCP and hydrogen bonds are structural features of micelles after HP treatment. Overall, HP-induced effects on casein micelles are probably the result of two discreet processes: (1) HP-induced solubilisation of CCP, resulting in disruption of casein micelles and (2) interactions between casein micelles and HP-denatured whey proteins, resulting in increases in micelle size.
Session 80, Ultra high pressure: Molecular changes in foods
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