Food Structure


Acid-heat-induced gels were obtained by coagulating casein micelle dispersions at 90 C using glucono-and-lactone. The casein micelles used were isolated from raw skim milk by centrifugation, washed free of whey proteins and soluble salts, and dispersed in water or a milk dialyzate. The pH values of the gels varied from 4.7 to 6.3. A core-and-lining ultrastructure developed in casein particles coagulated at pH 5.2 to 5.5 from casein micelle dispersions in the milk dialyzate provided that B-lactoglobulin or whey proteins (10 mg/ml) were added to them prior to coagulation. Addition of B-lactoglobulin to aqueous casein micelle dispersions led to the development of a considerably less distinct core-and-lining ultrastructure of the resulting gels. Coagulated casein particles obtained from casein micelle dispersions in water or in the milk dialyzate to which neither B-lacto-globulin nor whey proteins were added, did not show the core-and-lining ultrastructure but constained void spaces inside and were covered with loosely aggregated protein on the surface.

It was concluded that both B-lactoglobulin or whey proteins and the milk salt system are essential for the formation of the core-and-lining ultrastructure in the casein micelle dispersions gelled by heating at 90 C at pH 5.2 to 5.5.

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