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Growth characteristics of post-pasteurization contaminants isolated from pasteurized milk

Published online by Cambridge University Press:  01 June 2009

R. Gregory Stevenson ,
G. Brian Wisdom ,
Michael T. Rowe  and
Deirdre A. McConaghy
R. Gregory Stevenson
Affiliation:
Department of Food Science and Food Microbiology, The Queen's University of Belfast, Newforge Lane, Belfast BT9 5PX, UK
G. Brian Wisdom
Affiliation:
Division of Biochemistry, School of Biology and Biochemistry, The Queen's University of Belfast BT9 7BL, UK
Michael T. Rowe
Affiliation:
Department of Food Science and Food Microbiology, The Queen's University of Belfast, Newforge Lane, Belfast BT9 5PX, UK Department of Agriculture for Northern Ireland, Newforge Lane, Belfast BT9 5PX, UK
Deirdre A. McConaghy
Affiliation:
Biometrics Division, Department of Agriculture for Northern Ireland, Newforge Lane, Belfast BT9 5PX, UK
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Summary

Nine organisms were isolated from separate pasteurized milk samples after they had been incubated at 6 °C for 5 d (European Union preincubated count, PIC), four from high count samples (> 5 x 106 cfu/ml) and five from low count samples (< 103 cfu/ml). When the organisms were harvested without overt stress being applied and subjected to a simulated PIC using UHT whole milk, all except one isolate gave comparatively high (> 106 cfu/ml) counts. The imposition of a heat stress at 50 °C prior to a simulated PIC resulted in a segregation of the isolates into those giving high and those giving low counts, which reflected the PIC values of the milk samples from which they were originally isolated. When the isolates were subjected to a cold stress (25 to 4 °C) and inoculated into nutrient broth at 4 °C, the high count isolates were found to have significantly (P < 0·05) shorter lag phases than the low count isolates.

Type
Original Articles
Information
Journal of Dairy Research , Volume 63 , Issue 4 , November 1996 , pp. 585 - 591
Copyright
Copyright © Proprietors of Journal of Dairy Research 1996

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