| Popis: |
The formation of a maximum cream layer on bottled milk is a matter of much commercial importance as is well known. The advent of commercial pasteurization introduced many problems connected with the effect of heat on the creaming ability of milk. It is generally recognized that the usual pasteurizing temperatures of market milk are not detrimental to creaming, but they represent the upper limits before reduction of creaming occurs. Babcock and Russell (1) in 1896, and Farrington and Russell (2) in 1899, were among the first to recognize this fact. Dahlberg and Marquardt (3) (4) have presented an excellent review of work in this field. The work of several investigators, and in particular Troy and Sharp (5), has shown that clustering of fat globules is essential to rapid and exhaustive creaming. The failure of fat globules to cluster in milk which has been heated above a certain point results in a reduction in the cream volume. It remains to be shown what factors are important in promoting or preventing clustering. Palmer and Anderson (6) have shown that addition of milk albumin which increased the viscosity of the milk plasma accelerated creaming, while the addition of casein inhibited creaming. Rahn (7) suggests that this is caused by the heat inactivation of the sticky colloidal layer surrounding the fat globule. Sirks (8) found no apparent relation between creaming and the electrokinetic potential of the fat. In contrast to this, Dahlberg and Marquardt (3) have offered an explanation embracing an alteration in the magnitude of the charge on the particles. Numerous attempts by Hammer (9), Troy and Sharp (5), and others to promote clustering by altering the zeta potential through additions of electrolytes have been effective. |
