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Performance of a Growth–No Growth Model for Listeria monocytogenes Developed for Mayonnaise-Based Salads: Influence of Strain Variability, Food Matrix, Inoculation Level, and Presence of Sorbic and Benzoic Acid

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Abstract:

A previously developed growth–no growth model for Listeria monocytogenes, based on nutrient broth data and describing the influence of water activity (aw), pH, and acetic acid concentrations, was validated (i) for a variety of L. monocytogenes strains and (ii) in a laboratory-made, mayonnaise-based surimi salad (as an example of a mayonnaise-based salad). In these challenge tests, the influence of the inoculation level was tested as well. Also, the influence of chemical preservatives on the growth probability of L. monocytogenes in mayonnaise-based salads was determined. To evaluate the growth–no growth model performance on the validation data, four quantitative criteria are determined: concordance index, % correct predictions, % fail-dangerous, and % fail-safe. First, the growth probability of 11 L. monocytogenes strains, not used for model development, was assessed in nutrient broth under conditions within the interpolation region. Experimental results were compared with model predictions. Second, the growth–no growth model was assessed in a laboratory-made, sterile, mayonnaise-based surimi salad to identify a possible model completeness error related to the food matrix, making use of the above-mentioned validation criteria. Finally, the effect on L. monocytogenes of common chemical preservatives (sorbic and benzoic acid) at different concentrations under conditions typical of mayonnaise-based salads was determined. The study showed that the growth–no growth zone was properly predicted and consistent for all L. monocytogenes strains. A larger prediction error was observed under conditions within the transition zone between growth–no growth. However, in all cases, the classification between no growth (P = 0) and any growth (P > 0) occurred properly, which is most important for the food industry, where outgrowth needs to be prevented in all instances. The results in the sterile mayonnaise-based salad showed again that the growth–no growth zone was well predicted but that also, in real food systems, a transition zone between growth and no growth exists. This became even more obvious for lower inoculation levels. The maximum-allowed concentration of benzoic and sorbic acid in mayonnaise-based salads, according to the European Union legislation, eliminated the growth of L. monocytogenes. Concentrations of 600 and 300 ppm were already sufficient to inhibit growth at 7 and 4°C, respectively, under conditions associated with mayonnaise-based salads (pH 5.6; aw, 0.985).

Document Type: Research Article

Affiliations: 1: LFMFP, Laboratory of Food Microbiology and Food Preservation, Department of Food Safety and Food Quality, Ghent University, Coupure Links 653-9000 Ghent, Belgium 2: BioTeC, Chemical and Biochemical Process Technology and Control Section, Department of Chemical Engineering, Katholieke Universiteit Leuven, W. de Croylaan 46-3001 Leuven, Belgium 3: MeBioS, Division of Mechatronics, Biostatistics and Sensors, Department of Biosystems (BIOSYST), Katholieke Universiteit Leuven, W. de Croylaan 42-3001 Leuven, Belgium

Publication date: September 1, 2007

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    First published in 1937, the Journal of Food Protection®, is a refereed monthly publication. Each issue contains scientific research and authoritative review articles reporting on a variety of topics in food science pertaining to food safety and quality. The Journal is internationally recognized as the leading publication in the field of food microbiology with a readership exceeding 11,000 scientists from 70 countries. The Journal of Food Protection® is indexed in Index Medicus, Current Contents, BIOSIS, PubMed, Medline, and many others.

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