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Adaptability of the Fisher-Stern Ultracentrifuge in Studying the Sedimentability of Milk Proteins

Department of Food Technology, University of Illinois, Urbana

ABSTRACT

The Fisher-Stern Ultracentrifuge is a simple and relatively inexpensive centrifuge in which a plastic rotor spins in a vertical plane. The rotor is spun by a jet of air and the velocity is controlled by air pressure. The velocity is measured by an electronic tachometer with an accuracy of 1.5%.

Centrifugations were made in a room at 20–21° C. The thin cell was used for observation and pictures. The larger analytical cell was used to obtain samples of supernatant for analysis. Sedimentation times were taken as the time at which maximum depths of sediment were first attained as determined by measurement of pictures. The distance from the top of the cell to the top of the sediment represents the movement of the boundary. S values calculated by the application of the Svedberg equation,
ranged from 430 x 10^–13 to 57,000 x 10^–13. The value of 480 for a sample of untreated raw milk compares favorably with values 463 reported by Ford and Ramsdell (1) and 470 by Ford, Ramsdell and Landsman (2).