Type of Document Dissertation Author Lawlor, Kathleen A. URN etd-011899-164510 Title Effect of modified atmosphere packaging on growth of Listeria monocytogenes and nonproteolytic Clostridium botulinum in cooked turkey Degree PhD Department Food Science and Technology Advisory Committee
Advisor Name Title Pierson, Merle D. Committee Chair Claus, G. William Committee Member Claus, James R. Committee Member Hackney, Cameron Raj Committee Member Marcy, Joseph E. Committee Member Keywords
- Listeria monocytogenes
- modified atmosphere packaging
- nonproteolytic Clostridium botulinum
- cellular fatty acids
Date of Defense 1999-01-12 Availability restricted Abstract
The growth of Listeria monocytogenes and nonproteolytic Clostridium botulinum type B
spores in cooked, uncured turkey was investigated separately under varying conditions of
modified atmosphere packaging (MAP), refrigerated and temperature-abuse storage, and lactic
acid bacteria (LAB) competition. L. monocytogenes (LM) growth was suppressed when initially
outnumbered 3.5 logs:1 or 2.1 logs:1 by naturally-occurring LAB, but not when the initial
LAB:LM population ratio was equivalent. Lowering storage temperature from 10 degrees
to 4 degrees C enhanced the inhibitory effect of CO 2 in the packaging atmosphere, and extended the period of
product olfactory acceptability. When the LAB:LM population ratio was equivalent,
objectionable odors were not detected in most of the samples, despite LAB counts in excess of
10E8/g. This raises concerns with respect to public health, since high levels of L. monocytogenes
can be present in MAP meat and poultry products without accompanying signs of overt spoilage.
Cellular fatty acid (CFA) analysis was a valuable tool for distinguishing between
phenotypically distinct isolates of LM inoculated into MAP turkey. Fatty acid composition of
foodborne outbreak-associated (serotype 4) and non-outbreak-associated (serotype 1) strains of
LM correlated with antigenic type (4 or 1) and agglutination reaction (granular or flocculent).
Strain ATCC 43256 (serotype 4b) produced a consistently unique CFA profile, making it the
easiest of the four test strains to be differentiated. Analysis of additional LM serotypes, as well
as examination of existing clinical and environmental CFA databases for correlations between
fatty acid profiles and diagnostic characteristics of LM, is necessary before CFA analysis can be
effectively applied as an epidemiological tool for tracking the distribution of LM strains in food
products and throughout the farm-to-table food chain.
Reduced storage temperature significantly delayed botulinal toxin production and
extended the period of olfactory acceptability of cooked turkey, but even strict refrigeration did
not prevent growth and toxigenesis by nonproteolytic C. botulinum type B. Toxin was detected
on day 7 for product stored at 15 degrees C and on day 14 for product stored at 10 degrees C, irrespective of
packaging atmosphere. At 4 degrees C, toxin was detected on day 14 for product packaged without carbon dioxide,
and on day 28 for product packaged with 30% carbon dioxide. At all three storage temperatures, toxin
detection preceded or coincided with olfactory unacceptability, demonstrating the potential for
consumption of toxic product when spoilage-signalling sensory cues are absent.
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