Growth of Clostridium
perfringens during Cooling of Refried Beans
Outbreaks of Clostridium perfringens have been associated with dishes containing refried beans from food service establishments. However, growth of C. perfringens in refried beans has not been investigated, and predictive models have not been validated in this food matrix.
We investigated the growth of C. perfringens during the cooling of refried beans. Refried beans (pinto and black, with and without salt added) were inoculated with 3 log CFU/g C. perfringens spores and incubated isothermally at 12, 23, 30, 35, 40, 45, and 50°C. The levels
of C. perfringens were monitored 3, 5, 8, and 10 h after inoculation, and then fitted to the Baranyi primary model and the Rosso secondary model prior to solving the Baranyi differential equation. The final model was validated by dynamic cooling experiments carried out in stockpots,
thus mimicking the worst possible food service conditions. All refried beans samples supported the growth of C. perfringens, and all models fit the data with pseudo-R
2 values of 0.95 or greater and mean square errors of 0.3 or lower. The estimated maximum specific
growth rates were generally higher in pinto beans, with or without salt added (2.64 and 1.95 h–1, respectively), when compared with black beans, with or without salt added (1.78 and 1.61 h–1, respectively). After 10 h of incubation, maximum populations of
C. perfringens were significantly higher in samples with no salt added (7.9 log CFU/g for both pinto and black beans) than in samples with salt added (7.3 and 7.2 log CFU/g for pinto and black beans, respectively). The dynamic model predicted the growth of C. perfringens during
cooling, with an average root mean squared error of 0.44. The use of large stockpots to cool refried beans led to an observed 1.2-log increase (1.5-log increase predicted by model) in levels of C. perfringens during cooling. The use of shallower pans for cooling is recommended, because
they cool faster, therefore limiting the growth of C. perfringens.
Document Type: Research Article
Emerging Pathogens Institute and Department of Plant Pathology, University of Florida, 2055 Mowry Road, Gainesville, Florida 32611, USA; Centro de Investigaciones Biotecnológicas del Ecuador (CIBE), Escuela Superior Politécnica del Litoral (ESPOL), Campus Gustavo Galindo, Km. 30.5 vía Perimetral, Apartado 09-01-5863, Guayaquil, Ecuador
Department of Family, Youth, and Community Sciences, 3025 McCarty Hall, P.O. Box 110310, University of Florida, Gainesville, Florida 32611, USA
Department of Food Science and Human Nutrition, Citrus Research and Education Center, University of Florida, 700 Experiment Station Road, Lake Alfred, Florida 33850, USA
Department of Family, Youth, and Community Sciences, 3025 McCarty Hall, P.O. Box 110310, University of Florida, Gainesville, Florida 32611, USA. email@example.com
Publication date: October 1, 2012
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