Growth of Cronobacter spp. under Dynamic Temperature Conditions Occurring during Cooling of Reconstituted Powdered Infant Formula
Abstract:Reconstituted infant formulae are excellent growth media for Cronobacter spp. (formerly Enterobacter sakazakii) and other microorganisms that may be present in such products. Immediate consumption or rapid cooling and storage at a low temperature are therefore recommended as control measures to prevent microbial growth. Placing a container filled with reconstituted liquid formula in the refrigerator, however, does not mean that the temperature of the liquid is directly the same as the set-point of the refrigerator. This study describes the temperature profiles and methods to predict lag time and possible growth of Cronobacter spp. during the cooling process in three types of containers. The overall heat transfer coefficients (α) were determined and were shown to have a very large variability in both household refrigerators and an air-ventilated refrigerator equipped with a fan. A mathematical model was built to predict the growth of Cronobacter spp. under dynamic temperature conditions using three models for the lag time. The various estimations for the lag time had a remarkably strong impact on the predicted growth. The assumption of a constant k-value (k = lag time × specific growth rate = λ × μ = 2.88) fitted the experimental data best. Predictions taking into account the large variability in heat transfer showed that proliferation of Cronobacter spp. during cooling may be prevented by limiting the volume to be cooled to portion size only, or by reconstituting at temperatures of 25°C or lower. The model may also be used to predict growth in other situations where dynamic temperature conditions exist.
Document Type: Research Article
Affiliations: 1: Wageningen University, Laboratory of Food Microbiology, P.O. Box 8129, 6700 EV Wageningen, The Netherlands 2: Nestlé Product Technology Centre Konolfingen, Applied Science & Analytical Support Department, Nestlé Strasse 3, P.O. Box 12, CH-3510, Konolfingen, Switzerland 3: Wageningen University, Laboratory of Food Microbiology, P.O. Box 8129, 6700 EV Wageningen, The Netherlands, Unilever, SEAC, Colworth Science Park, Sharnbook MK44 1LQ, UK 4: Wageningen University, Laboratory of Food Microbiology, P.O. Box 8129, 6700 EV Wageningen, The Netherlands;, Email: Martine.Reij@wur.nl
Publication date: December 1, 2009
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