Psychrophilic Bacteria. III. Population Levels Associated with Flavor or Physical Change in Milk

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Abstract
Psychrophilic cultures (57) were studied to determine population levels at the time a flavor or physical change in pasteurized milk was detected. Populations associated with a detectable change varied among genera and species within a genus. These levels were usually in a range of 5 to 20 million/ ml at the time a change was observed; more active cultures were below and less active ones above this range. The most commonly observed flavor defect was unclean. Slight changes detectable organoleptically were not detectable by chemical measurement of fat or protein hydrolysis. One culture of Alcaligenes viscolactis produced ropiness, with no detectable flavor change at population levels below 5 million/ml. When oxidized and strong feed flavors were present, these flavors were markedly reduced by growth of each of several cultures to a population level just below that at which a characteristic flavor defect occurred. Approximately the same population levels were associated with change at 6 and 20 C.