Modelamento preditivo para crescimento de Listeria monocytogenes aplicável a salsicha.

Abstract

The effect of storage temperature, pH, content salt and nitrite on the growth of Listeria monocytogenes was investigated using predictive models applicable to the frankfurters, since this is one of the foods most involved in food outbreaks caused by this pathogen. For each incubation temperature studied, 10, 15 and 37°C, the effect of factors pH, NaCl and NaNO2 on growth of L. monocytogenes was investigated. For each factor, two levels were analyzed: pH 5,5 and 6,8; 1,5 and 2,0 g/100g NaCl; 75 and 150 mg/kg NaNO2. For each culture media the absorbância (turbidity) was measured by means of spectrophotometer at 630 nm, specific for microplate reader, at time intervals of about 2 h until the growth reached absorbance between 0.600 and 0.700 or when the reading became inconsistent. Using the MatLab software, the obtained data were adjusted to growth curves for three models: Gompertz, Logistic and Logistic modified. The adequacy of fit of the data onto models was evaluated using Bias Factor and Accuracy Factor and also by a residue analysis. In general, the three growth curves showed a good fit, using culture media without inhibitors for the growth of Listeria monocytogenes and using the culture media with the different levels of factors studied as well, with determination coefficients (R2 ) greater than 0.94. Gompertz model showed Bias Factors and Accuracy Factors values closer to 1, indicating a better fit, in addition obtain lower specific growth rate (μmax) values and adaptation phase values (λ), but these parameters are similar in different models. However, the Gompertz model residue graphs profile showed greater inconsistencies than the Modified Logistic model, which was adopted as a predictive model to describe the growth of Listeria monocytogenes. In the Modified Logistic Model, the Lag phase (λ) decreased as the incubation temperature increased, the Specific Growth Rate (μmax) and the Relative Growth Rate (B) increased with increasing incubation temperature in most culture media studied. According to this model, increasing the salt content of the culture media to 2.0 g / 100 g, growth of L. monocyogenes could be reduced even lowering the sodium nitrite content to 75 mg / kg.