A predictive model of growth from
spores of non-proteolytic Clostridium
botulinum in the presence of di¡erent
CO
2
concentrations as in£uenced by
chill temperature, pH and NaCl
P. S. Fernandez*,J.BaranyiandM.W.Peck
In the present study, the e¡ect of modi¢ed atmospheres ranging from 0^90% CO
2
(balance 10% H
2
and
N
2
) was evaluated on growth from spores of non-proteolytic Clostridium botulinum (t ypes B, E and F),
at di¡erent pH and NaCl concentrations, over the temperature range 5^128C. Growth tests were carried
out using a model broth system, PYGS (peptone, yeast, glucose, starch). In general terms, a CO
2
con-
centration of 5% enhanced growth, 50% CO
2
showed a moderate inhibition and 90% had a consider-
able inhibitory e¡ect. A predictive model has been developed that describes the e¡ect of CO
2
,
in combination with other mild preservative factors, on growth from spores of non-proteolytic
C. botulinum. The model provides a good description of the experimental data.
# 2001Academic Press
Introduction
In Europe, consumer demand for natural, high
quality products is growing, and new food pro-
ducts are continuously appearing to meet this
demand. For such products, it is important that
only mild preservative techniques are used,
and that they impact on the natural character-
istics and £avour as little as possible. The
safety of these foods usually relies on a mini-
mal heat treatment and storage at refrigera-
tion temperatures, although there is much
interest in the additional use of modi¢ed (low
oxygen) atmospheres and other mild preserva-
tive factors. The successful use of modi¢ed at-
mospheres and other mild preservative factors
requires a quantitative assessment of their
e¡ectiveness against the principal microbiolo-
gical hazards.
The principal microbiological concern for
the safe production of refrigerated processed
foods of extended durability (REPFEDs) is
non-proteolytic Clostridium botulinum (Peck
1997, Peck 1999, Lund and Peck 2000). This
pathogen grows and produces neurotoxin at
3?08C (Graham et al. 1997), consequently, the
chill chain alone may not be su⁄cient to pre-
vent growth and toxin production. There is a
risk that spores of non-proteolytic C. botulinum
may survive the mild heat treatments given to
REPFEDs (Peck and Fernandez 1995). Predic-
tive models have been developed that can be
used to estimate the shelf-life of these foods in
ORIGINAL ARTICLE
*Corresponding author. Present address: Escuela
Tecnica Superior de Ingenieria Agronomica, Univer-
sidad Politecnica de Cartagena, Paseo Alfonso XIII,
48, 30203 Cartagena (Murcia), Spain.
Fax:+34 968 325433. E-mail: pablo.fernandez@upct.es
Received:
22 February 2001
Institute of Food
Research, Norwich
Research Park,
Colney, Norwich,
NR4 7UA, UK
0740-0020/01/080453 +09 $35.00/0 # 2001 Academic Press
Food Microbiology, 2001, 18, 453^461 doi:10.1006/fmic.2001.0425
Available online at http://www.idealibrary.com on