Title page for ETD etd-011899-164510


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
  • turkey
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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