Model for the combined effects of temperature, pH, and sodium lactate on growth rates of Listeria innocua in broth and Bologna-type sausages

Abstract

A modified Monod equation was successfully applied to describe the maximum specific growth rate of Listeria innocua in a broth model in the presence of various concentrations of sodium lactate or NaCl. The combined effects of temperature and pH were assessed by translating the parameters of the modified Monod equation (m , ␣, and p) as functions of pH and/or temperature. As a result, the area in which the growth rate could be predicted was extended to include as a variable not only the salt concentration but also pH and temperature. The number of parameters needed to describe the experimental data was thereby reduced from 48 to 4 (NaCl) and from 42 to 5 (sodium lactate). The decline in the goodness of fit that accompanied the reduction in the number of parameters was within statistically acceptable ranges. The resulting model was compared with a polynomial fit, and it was proposed that the former was more suitable for the purpose of this study. The broth model for sodium lactate was evaluated with Bologna-type sausages. Because of the ''worstcase'' design of the broth model, it was necessary to reestimate one or all parameters to obtain a good description of the growth rate of L. innocua in the meat product. However, the simplicity of the model and the practical usefulness of its parameters offer considerable prospects for its use in predictive microbiology.

Modeling Growth and Reduction of Microorganisms in Foods as Functions of Temperature and Time

“…Many models have been developed for predicting the growth of Listeria in foods under various conditions of temperature, pH, salt content, and sodium nitrite content, such as Buchanan and Phillips, ( 2 ) Houtsma et al , ( 3 ) Conner et al , ( 4 ) Le Marc et al , ( 5 ) and Tamplin. ( 6 ) The model by Tamplin is offered by the U.S. Department of Agriculture with a preprogrammed graphical user interface and generates graphs and tabular output for various growth parameters.…”

Development and Validation of a Predictive Model for Listeria monocytogenes Scott A as a Function of Temperature, pH, and Commercial Mixture ofPotassium Lactate and Sodium Diacetate

“…Both quadratic and cubic polynomial models for SGR and LT provided acceptable predictions of L. monocytogenes Scott A growth in the matrix of conditions described in the present study. Model performance can be more accurately evaluated with B f and A f and % RE together.Predictive growth modeling of L. monocytogenes has received a lot of attention [2,9,16] because of listeriosis outbreaks, predominantly associated with ready-to-eat (RTE) food. If models can be developed to give reliable predictions, considerable savings can be made in costs associated with laboratory challenge testing of food products.…”

“…Keywords: L. monocytogenes Scott A, polynomial model, model validation, potassium lactate/diacetate mixture, temperature Predictive growth modeling of L. monocytogenes has received a lot of attention [2,9,16] because of listeriosis outbreaks, predominantly associated with ready-to-eat (RTE) food. If models can be developed to give reliable predictions, considerable savings can be made in costs associated with laboratory challenge testing of food products.…”

“…They are commercially available in liquid (60% wt/wt) form and are widely used in processed meat formulations. Consequently, lactate and diacetate have been incorporated as a variable in the mathematical models to predict various products safety, including cooked meat products [7,12], bologna-type sausages [9], beef [11], lightly preserved seafood [15], frankfurter slurry [21], and cured processed meat products [22]. In addition, a commercially used product known as PURASAL P Opti.Form 4, which is a combination of potassium lactate (PL) with sodium diacetate (SDA), was used effectively to control L. monocytogenes Scott A in broth [1] and in a cold smoked salmon model [26,28].…”

Modeling the Growth Rate of Listeria Monocytogenes Using Absorbance Measurements and Calibration Curves

“…The toxicity of organic acids is primarily caused by the hydrogen ion concentration in media, that is, pH, and secondly and the most important factor, by the action of the undissociated molecule (Nyati 2000; Phan‐Thanh and others 2000). Undissociated acids are able to penetrate into the cell, lowering the intracellular pH and thereby causing inhibition (Houtsma and others 1996). Therefore we should expect greater inhibition of L. monocytogenes growth at higher concentrations of undissociated acid (u.a.c.)…”