Studies on the Psychrotrophic Bacteria Contaminating Raw Pork

Abstract

Microbiological studies were made on the muscle tissue of 10 swine obtained at an abatoir. Serial psychrotrophic bacterial counts were made at regular intervals on the specimens kept at 5 and 10°C for a period of 10 days. The methods adopted for the enumeration of psychrotrophic organisms were those widely used by the dairy microbiologists, and the determination of proteolytic and lipolytic activities of the isolates were made by the use of milk agar and Crossley agar plates, respectively.The results obtained are summarized as follows:1) Psychrotrophic bacterial counts obtained by the use of several different determination methods agreed well one another.2) Serial psychrotrophic bacterial counts in the specimens had indicated the gradual propagation of the organisms at 5°C, i. e., the counts reached at the order of 108 organisms per gram of meat after 7 days of the storage, however, the meat stored at 10°C for 3 days was found to have already involved about 109 organisms in one gram of sample, and the increase in pH value and rotten odors were also observed.3) About 70% of the initial isolates of the meat were comprised in gram-negative bacteria, such as Pseudomonas, Flavobacterium, Achromobacter and others, however, after the 7 days of storage at 5°C, more than 90% of the isolates were found to have been replaced by Pseudomonas.4) Most of the initial isolates grew well between 10-35°C. However, gram-negative strains tended to grow better at or below 30°C and gram-positive strains at or above 35°C. Most of Pseudomonas isolated from the meat stored at 5°C grew well between 0-30°C, but not at 35°C.5) About 25% of the psychrotrophic isolates manifested proteolytic activities. On the other hand, about 31% of the isolates exhibited weak lipolytic activities, while 14% showed both proteolytic and lipolytic activities