The effect of lipid type on the amount and profile of proteins adsorbed at the lipid serum interface in homogenized milk systems was studied. Lipid sources were milkfat, butter oil, corn oil and a commercial system used for vitamin A and D milk fortification. Protein adsorption with the commercial system was significantly lower than with the other systems, which exhibited similar protein concentrations. Inclusion of vitamin A (all-trans retinyl palmirate) alone or in combination with Tween 80 or distilled monoglycerides in corn oil decreased significantly the amount of proteins adsorbed. Both casein and whey proteins were adsorbed at the lipid serum interface. Casein composed more than 96% of the total milk proteins adsorbed. Among whey proteins, β-lactoglobulin was the dominant protein. The ratios for the three caseins in the adsorbed film were different from their proportions in the serum phase; β-casein was present in higher concentrations, followed by α(s)and κ-casein, respectively.
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Vitamin A, all-trans retinyl palmitate, added to lowfat milk via an oil carrier system is more susceptible to light degradation than the naturally occurring vitamin A (Thompson & Erdody, 1974; deMan, 1981; Bartholomew & Ogden, 1990). Type of oil carrier system used to incorporate vitamin A affects the light ‘Published as Paper No. 19,588 of the contribution series of the Minnesota Agricultural Experiment Station based on research conducted under Project 18-24, supported by University of Minnesota Computer Center and National Dairy Promotion and Research Board. *To whom correspondence should be addressed (Tel.: 612-624-3260; Fax: 612-625-5272).
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