Title: Influence of Incubation Temperature on the Growth of Psychrotrophic Bacteria Isolated from Frozen Pork
Abstract: Growth temperature characteristics of 10 strains of psychrotrophic bacteria, which consisted of each 2 strains of Pseudomonas sp. (fluorescent type), Pseudomonas sp. (nonfluorescent type), Flavobacterium sp., Coryneforms sp. and Micrococcus sp., isolated from frozen pork were studied, since these 5 strains had been the most predominant contaminants of the frozen meat. Growth curves obtained on the 10 strains at varying temperatures covering 0 to 50°C with 5°C intervals were compared with those of 8 reference strains of stock cultures, Pseudomonas fluorescens, Pseudomonas fragi, Flavobacterium suaveolens, Cytophaga (Guppy B), Escherichia coli, Microbacterium thermosphactum, Micrococcus caseolyticus and Staphylococcus aureus. A temperature gradient incubator model TN-3 of Toyo Kagaku Sangyo Co. was used in this experiment.Regardless of the genera of the organisms minimum temperatures for the growth of all the isolates tested were below 0°C and the optimum ones were 25 or 30°C. The minimum generation time of the isolates varied from 29 to 65min. Among these isolates, both Pseudomonas fluorescent types and non-fluorescent ones showed maximum growth temperatures of 35 and 40°C respectively, while those of the other organisms were 30°C. The growth rates of the psychrotrophic stock strains at 0°C were a little lower than those of the Pseudomonas sp. of the isolates.