Survival curves of heated bacterial spores: effect of environmental factors on Weibull parameters

Abstract

The classical D-value of first order inactivation kinetic is not suitable for quantifying bacterial heat resistance for non-log linear survival curves. One simple model derived from the Weibull cumulative function describes non-log linear kinetics of micro-organisms. The influences of environmental factors on Weibull model parameters, shape parameter "p" and scale parameter "delta", were studied. This paper points out structural correlation between these two parameters. The environmental heating and recovery conditions do not present clear and regular influence on the shape the parameter "p" and could not be described by any model tried. Conversely, the scale parameter "delta" depends on heating temperature and heating and recovery medium pH. The models established to quantify these influences on the classical "D" values could be applied to this parameter "delta". The slight influence of the shape parameter p variation on the goodness of fit of these models can be neglected and the simplified Weibull model with a constant p-value for given microbial population can be applied for canning process calculations.

Survival of Campylobacter jejuni in mineral bottled water according to difference in mineral content: Application of the Weibull model

“…Results showed that the p parameter associated to the shape of survival curves was dependent from the type of preculture as it was supposed by Couvert et al (2005). Concave upward survival curves were observed for all kinetics and attested by a p value superior to one.…”

“…This equation was used by different authors (Mafart et al, 2002;Virto et al, 2005;Carlin et al, 2006;Buzrul, 2007) and was implemented in this work as primary model. The shape parameter p variation on the goodness of fit of models was shown by Couvert et al (2005) to have slight influence so that a single pvalue can be used for a given microbial population (same physiological state, same preculture) (Couvert et al, 2005). A single overall estimation of p-value per strain was determined, regardless of environmental conditions (water type) and recovery (medium used for colony counting), as it seemed to be enough for bacterial food predictive modelling and canning process calculation (Mafart et al, 2002 …”

“…In our experiments, a single p-value was calculated and used to describe the survival of a given strain after a given preculture in order to evaluate the influence of water mineral content on Campylobacter survival using two different media for viable counts. The parameter values and their associated confidence interval were fitted by using a non-linear module (bnlinfitQ and bnlparciQ Matlab 6.1, The Mathworks) (Couvert et al, 2005). To appreciate the accuracy on the non-linear models used in this study F test and associated probability p were carried out.…”

Teaching microbiological food safety through case studies

“…Some common models, like Bigelow or Mafart models (Couvert, Gaillard, Savy, Mafart, & Leguerinel, 2005) were described. In tutorials, students could evaluate which parameter had the highest impact on the logarithmic destruction of a microbial population when several factors varied together.…”

Thermal Inactivation of Geobacillus Stearothermophilus Spores Under Sterilization Process

“…Podobnie Couvert i wsp. [1] twierdzą, że w przypadku nieliniowego przebiegu krzywej przeżycia spor, odczytywanie wartości D z odcinka przebiegającego według reakcji I rzędu do określenia ciepłooporności mikroorganizmów jest nieodpowiednie i obarczone dużym błędem.…”