Influence of Temperature on Some Biochemical Characteristics of Pseudomonas Associated with Spoilage of Chicken

Abstract

SUMMARY Studies were conducted with four cultures of Pseudomonas isolated from frozen chicken. The effect of temperature on some biochemical activities of the organisms was evaluated and the individual response of the cultures to temperature was determined. Growth, survival and production of the green fluorescent pigment, pyoverdine, and extra‐cellular proteinase and lipase activities were used as indices of the ability of pseudomonads to produce spoilage. The four isolates differed in their ability to perform the metabolic functions mentioned. The cultures were incubated at 15°, 5°, −18°, and −29°C. Assays for proteolysis were made by means of a dye binding method; lipolysis was determined by titration of free fatty acids released from chicken fat, and a photo‐fluorometer was used to measure fluorescent pigment. Growth was determined by colony count. At temperatures above 0°C, survival was better and growth and enzyme activity were more extensive at 5° than at 15°C. Proteinase activity increased continuously, even when viable cells were decreasing; lipase production was correlated with growth. Formation of pyoverdine declined faster than did cell numbers. Survival of the cultures was better at −18° than at −29°C, Impairment of pyoverdine secretion was observed after exposure of the organisms to freezing temperatures, but the activity of the extracellular enzymes was not affected at temperatures below 0°C. No marked differences were observed among cultures in rate of cell division, but maximum populations, survival of organisms and stability of the proteolytic, lipolytic and fluorescent activities of the isolates were inversely related to biochemical activity above 0°C.

Effect of Freezing and Packaging Methods on Survival and Biochemical Activity of Spoilage Organisms on Chicken

“…Consideration must be given to earlier observations made in this laboratory (Rey et al, 1969) that psychrophilic Pseudomonas may differ considerably in their metabolic spoilage activity; this may partly explain the discrepancy reported by Kitchell and Ingram (1956) between some of their results and those of Sulzbacher (1952). When selected pure cultures are used as inocula at levels which form a major portion of the microflora, differences may be expected when compared with spoilage caused by naturally occurring contaminants present in their usual populations.…”

“…Lipolysis was evaluated by titration of free fatty acids released from chicken fat. For this test, the dialyzed wash water was analyzed for enzyme activity with chicken fat as substrate, in accordance with the method of Rey et al (1969). 4 ml of sample were employed for each test.…”

“…As mentioned earlier, the most metabolically active spoilage organisms may be expected to survive freezing to a greater extent than less active psychrophiles. The survivors subsequently could cause deterioration of poultry meat after thawing; such activity might be enhanced because fewer competing bacteria would be present than on unfrozen chicken (Rey et al, 1969).…”

New Medium for the Isolation and Enumeration of Pseudomonads1

“…Microorganisms of the genus Pseudomonas are often responsible for food spoilage during refrigerated storage (4,6,7,11,13,15). Pseudomonads are the predominant microorganisms present on fresh meat after several days of refrigerated storage (4,7,8).…”

Numerical taxonomy and changes of the bacterial flora on frozen chicken

“…Bacterial death due to freezing causes some reduction in numbers of bacterial populations (Kitchell amd Ingram, 1956;Elliott and Michener, 1960;Rey et , 1969). Freezing may also cause nonlethal injury to bacterial cells which is detected by chsmges in their metabolic functions (Straka and Stokes, 1959).…”