Impact of strain variability on the risk presented to chilled foods by non-proteolytic clostridium botulinum
type: CreativeWork
description: This PhD thesis aims to extend the current quantitative microbial risk assessment for minimally heated chilled foods by including information on variability of non-proteolytic Clostridium botulinum at strain level. The research on strain variability covers practical experiments as well as literature surveys and focuses on heat resistance properties of non-proteolytic C. botulinum spores, variability in growth at chill temperatures and variability in growth and neurotoxin formation in the presence of different carbohydrates. A strain classification pattern was developed and compared with published literature information on the genetic variation of non-proteolytic C. botulinum. Results for the growth at chill temperatures and from the carbohydrate study provide strong evidence of significant variability for strains of non-proteolytic C. botulinum that is associated with the type of neurotoxin formed. Although a literature review on heat resistance did not show correlation between the decimal reduction time and toxin type for non-proteolytic C. botulinum it provides a strong quantitative support for modelling of the thermal properties of the spores. Insights on strain variability were included in a modular quantitative microbial risk assessment (QMRA) for a model dairy-based chilled dessert using a Monte Carlo simulation technique. The model considered four steps in product manufacture that either reduced or increased the hazard associated with non-proteolytic C. botulinum: spore load in raw material, thermal inactivation of spores, distribution of spores in retail units and population kinetics for non-proteolytic C. botulinum during multi-stage storage regimes. The replacement of a commonly applied assumption on strain homogeneity with strain specific characteristics of non-proteolytic C. botulinum revealed that inclusion of information on strain variability has an important impact on estimated risks. The QMRA indicated that, for a minimally heated dairy-based dessert…
abstract: This PhD thesis aims to extend the current quantitative microbial risk assessment for minimally heated chilled foods by including information on variability of non-proteolytic Clostridium botulinum at strain level. The research on strain variability covers practical experiments as well as literature surveys and focuses on heat resistance properties of non-proteolytic C. botulinum spores, variability in growth at chill temperatures and variability in growth and neurotoxin formation in the presence of different carbohydrates. A strain classification pattern was developed and compared with published literature information on the genetic variation of non-proteolytic C. botulinum. Results for the growth at chill temperatures and from the carbohydrate study provide strong evidence of significant variability for strains of non-proteolytic C. botulinum that is associated with the type of neurotoxin formed. Although a literature review on heat resistance did not show correlation between the decimal reduction time and toxin type for non-proteolytic C. botulinum it provides a strong quantitative support for modelling of the thermal properties of the spores. Insights on strain variability were included in a modular quantitative microbial risk assessment (QMRA) for a model dairy-based chilled dessert using a Monte Carlo simulation technique. The model considered four steps in product manufacture that either reduced or increased the hazard associated with non-proteolytic C. botulinum: spore load in raw material, thermal inactivation of spores, distribution of spores in retail units and population kinetics for non-proteolytic C. botulinum during multi-stage storage regimes. The replacement of a commonly applied assumption on strain homogeneity with strain specific characteristics of non-proteolytic C. botulinum revealed that inclusion of information on strain variability has an important impact on estimated risks. The QMRA indicated that, for a minimally heated dairy-based dessert…
author: Wachnicka, Ewelina
language: en
date published: 2014-02
date modified: 2026-07-24T02:12:01Z
provider: University of East Anglia
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of East Anglia