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S. SANDRA, Y. D. Livney, and D. G. Dalgleish. Dept. of Food Science, Univ. of Guelph, Ontario Agricultural College, Guelph, ON N1G 2W1, Canada Ultra high pressure homogenization (UHPH) at pressures >34.5 MPa has been shown to produce finer emulsions, modify fat globules, cause protein denaturation and/or complex formation. Utilization of this technology alone or in combination with other treatments shows potential to produce new value-added products. Many studies have been done on homogenization effects on whole milk and its properties. However, only a few publications are available on UHPH of skim milk, and especially on its effect on casein micelle structure and properties. The objectives of this research were to investigate the effects of UHPH on skim milk with or without heat treatment and of the order of treatments on micelle size and properties, and on casein-whey protein complex formation. UHPH was done at 186 (±7) MPa, up to six passes and an inlet temperature of 25°C. The treatments employed were UHPH (H), heat treatment (T) of 85°C (±1°C) for 10 minutes, UHPH then heat (HT), heat then UHPH (TH), and control. Dynamic light scattering, rennet-clotting time (RCT), Transmission Electron Microscopy, size exclusion chromatography of supernatant, and SDS-PAGE were performed. Casein micelle size decreased with number of passes; the effect was most pronounced in unheated milk. RCT of control and H milks were significantly different. No clotting was observed (up to 25 minutes) in heated milk. However, when milk was heated and passed six times through UHPH, rennet clotting was observed. The casein-whey protein complex formed was found to be smaller in H than in T. HT and TH caused a similar, but more extensive, complex formation than in T. The amounts of serum soluble protein decreased in the following order: Hpass6>control>THpass6>Hpass6T>T. In conclusion, UHPH causes modifications of the properties of milk protein and the order of treatments employed is important. This study highlights potential of UHPH for research and dairy products development.
Session 64, Dairy Foods: Milk proteins
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