76D-10 |
Modeling the fluorescent decay of R-phycoerythrin: A possible time-temperature integrator to monitor thermal processing of beef products |
A. ORTA-RAMIREZ1, S. Vaidya2, R. Y. Ofoli1, and D. M. Smith3. (1) Dept. of Food Science and Human Nutrition, Michigan State University, East Lansing, MI 48824, (2) Dept. of Chemical Engineering, Michigan State University, East Lansing, MI 48824, (3) Dept. of Food Science and Toxicology, University of Idaho, Moscow, ID 83844 The USDA-FSIS has proposed a modification of the current thermal processing regulations for meat products. Processors deviating from compliance guidelines must provide evidence that a process meets lethality performance standards, expressed as log reductions in Salmonella. Pathogen inactivation models based on isothermal laboratory tests in sealed containers may not predict results in real commercial processes. Moreover, processors cannot take pathogens into production facilities and conduct challenge studies on actual processing equipment. A time-temperature integrator (TTI) that can predict destruction of Salmonella in meat products could be used to determine the adequacy of a thermal process and eliminate these problems. The goal of this work was to evaluate R-phycoerythrin (R-PE), an algal protein, as a TTI for ascertaining the degree of thermal inactivation of Salmonella during processing of beef products. Thermally induced fluorescence decay of R-PE was measured using isothermal experiments to determine the reaction kinetics at 60.0, 62.5, 65.0, 67.5 and 70°C. A general nth order kinetic model was developed, after initial analysis showed that the decay was not a linear reaction. Utility of the model was assessed by predicting the degree of inactivation of R-PE during non-isothermal experiments using protocols modeled after published USDA guidelines for cooked beef products. The rate of isothermal fluorescence decay was highly dependent on temperature. The reaction order was 2.27. Under non-isothermal conditions, good agreement was obtained between theory and experiment at temperatures ³65°C, although the model under-predicted the extent of fluorescence emission decay at 60°C and 62.8°C. Slow decay kinetics at these temperatures made it difficult to precisely measure small differences in fluorescence emission at the selected process times. R-PE fluorescence decay was well behaved and predictable. It should be possible to develop a correlation between Salmonella inactivation and residual R-PE fluorescence emission, to provide a tool for predicting destruction of microorganisms during thermal processing of beef products.
Session 76D, Muscle Foods II
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