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Department of Food Technology, University of Illinois, Urbana
ABSTRACT
Ultracentrifugation studies of milk sterilized by ultrahigh temperatures have shown that sedimentation constants increased. Sedimentation studies of reconstituted concentrated milks showed that milks reconstituted immediately after concentration had sedimentation constants approximately the same as the milks after preheating. Constants of the same milks reconstituted after sterilization were much higher. This study was undertaken to determine the relationship between concentration and size of particle after sterilization at a given temperature. To minimize the interference of fat in the determination of sedimentation constants, fat was removed by centrifugal separation of the raw milk at 100· F. Preheating (180· F., 4.16 sec.) and sterilization (293· F. no hold) temperatures used had been found to cause minimum clustering of protein particles. Portions of the preheated milk were concentrated 3:1, 2:1, and diluted one-third with deionized water. Logs of the sedimentation constants of the reconstituted sterile concentrated milks and sterile normal and diluted milks, when plotted against concentration, formed a straight line which intersected the zero concentration axis at the log of the sedimentation constant of the smallest micelle in raw skimmilk, reported by Ford and Eamsdell (1). The relationship of the particle size to sedimentation constant can be expressed by the equation
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