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M. X. SÁNCHEZ-PLATA, Dept. of Poultry Science, Texas A&M Univ., 338 Kleberg Center, College Station, TX 77843, A. Amézquita, Dept. of Biological Systems Engineering, Univ. of Nebraska Lincoln, 157 L.W. Chase Hall, Lincoln, NE 68583-0726, and H. Thippareddi, Dept. of Food Science & Technology, Univ. of Nebraska, Lincoln, 236 Food Industry Complex, Lincoln, NE 68583-0919. Spores of foodborne pathogens can survive traditional thermal-processing schedules used in the manufacturing of processed meat products. Heat activated spores can germinate and grow to hazardous levels if these products are improperly chilled. The objective of this project was to develop predictive models to describe germination and outgrowth of Clostridium perfringens spores during exponential cooling of cured and non-cured roast beef. Isothermal growth of C. perfringens was determined at 15 different constant temperatures (from 10 to 47ºC) in commercially formulated cured and non-cured roast beef. Primary modeling was achieved by fitting experimental data to the Baranyi's non-autonomous differential equation and the implicit form of the Gompertz model. Growth kinetic parameters for C. perfringens outgrowth under isothermal conditions were determined. The square-root Ratkowsky equation was used for secondary modeling to describe C. perfringens growth as a function of temperature change (dynamic cooling). The first order differential equations derived from primary and secondary models were solved using the fourth-order Runge-Kutta method. Dynamic cooking and cooling profiles obtained from a roast beef processor were used to validate predictive models. Germination and outgrowth of C. perfringens spores were evaluated in roast-beef samples cooled from 54.5 to 7.2ºC in 9, 12, 15, 18, 21, and 24 h. In general, the C. perfringens predictive model for non-cured roast beef accurately predicted growth of C. perfringens from spore inocula during exponential cooling. The model overpredicted (“fail-safe”) in some validation trials by < 0.75 log10 CFU/g. The predictive model for cured roast beef slightly overpredicted C. perfringens growth during cooling of roast beef within 15, 18, 21, and 24 h, and underpredicted (“fail-dangerous”) during cooling from 54.5 to 7.2ºC within 12 h (0.39 log10 CFU/g). The use of these equations in commercial settings will enable processors and regulators to evaluate safety of commercially produced cured/ non-cured roast beef.
Session 33, Food Microbiology: General
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |