Influence of Temperature on the Development of Several Psychrophilic Bacteria of Dairy Origin

Abstract

The importance of psychrophilic bacteria in the dairy field has been recognized for half a century (Bi- schoff, 1903; Conn, 1903).While perhaps not growing optimally, these organisms are capable of considerable development at refrigerator temperatures and may con- stitute a serious commercial and legal problem.Many species attack milk constituents and produce undesir- able flavors and odors.Others grow on the surface of products like butter and cottage cheese and develop a slimy or discoloration defect.Certain species, which produce no detectable change, may multiply rapidly during refrigerated storage and may raise the bacterial count above that acceptable as a legal maximum.This problem has recently received considerable at- tention due to commercial innovations which save labor but necessitate the holding of dairy products in storage for longer periods of time.The prolonged holding periods between the time of commercial processing and actual consumption and their effect on the numbers and types of milk flora have been investigated by Dahlberg (1946), Burgwald and Josephson (1947), Erdman and Thornton (1951) and Parker, Caldwell, and Elliker (1953).It has been found that most dairy psychrophiles are members of the Pseudomonas, Achromobacter, and Flavobacterium genera (Jezeski and Macy, 1946) and that the most probable sources of contamination are soil, water, and