Growth/no growth model of Listeria monocytogenes as a function of temperature, pH, citric acid and ascorbic acid

• Published in: European food research & technology Vol. 224; no. 1; pp. 91 - 100
• Main Authors: Valero, A, Carrasco, E, Pérez-Rodriguez, F, García-Gimeno, R. M, Zurera, G
• Format: Journal Article
• Language: English
• Published: Heidelberg Berlin/Heidelberg : Springer-Verlag 01.11.2006; Berlin Springer; Springer Nature B.V
• Subjects: Acids; ambient temperature; ascorbic acid; Bacteria; Biological and medical sciences; citric acid; food contamination; Food industries; Food microbiology; food pathogens; food safety; Food science; Fundamental and applied biological sciences. Psychology; General aspects; Growth models; Hygiene and safety; linear models; Listeria; Listeria monocytogenes; Low temperature; microbial growth; model validation; Organic acids; regression analysis; Temperature; Probability model; Temperature; Ascorbic acid; Growth; Predictive microbiology; Vitamin; Listeria monocytogenes; pH; Bacteria; Models; Food safety; Citric acid
• ISSN: 1438-2377; 1438-2385
• DOI: 10.1007/s00217-006-0293-1

A linear logistic regression model was built to describe the growth/no growth boundaries of Listeria monocytogenes as a function of temperature (4-30 °C), pH (4.5-6), citric acid (0-0.4%) and ascorbic acid (0-0.4%). A fractional factorial design was followed among the factors considered and an inoculum size of 10⁵ CFU/ml was used. Evaluation of growth was performed by optical density measurements in Bioscreen C (Labsystems, Finland), during 21 days. Data of optical density were transformed to log CFU/ml by using a calibration curve. Among the 232 combinations of factors tested, growth was observed in 133 and no growth in 99. The degree of agreement between predictions and observations was 97.8% concordant and 2.2% discordant. An internal validation with additional data within the interpolation region of the model was performed. The predictions were concordant in 94% of the cases, and all the wrong cases failed to the safe side of the boundary region. The probability of growth was strongly influenced at low temperatures (<15 °C). The effect of pH was more notorious below 5.3, since the minimum temperature that inhibited growth was higher. Citric acid was more effective than ascorbic acid when the analysis was based on the undisssociated acid concentration (u.a.c.). However, when dealing with the undissociated fraction (u.a.f.), ascorbic acid presented more inhibitory effect. Organic acids also accentuate the temperature and pH inhibition of bacterial growth limits, and increased the minimum pH at which growth was detected. These results have a practical implication for stakeholders and risk managers in order to identify the treatments that can be applied to food and ensure that no growth of this pathogenic microorganism will occur.