33-3 |
Evaluation by calorimetry the inactivation of microorganisms |
G. KALETUNĒ, Dept. of Food, Agricultural & Biological Engineering, The Ohio State University, 590 Woody Hayes Dr., 210 Agricultural Engineering Bldg., Columbus, OH 43210-1058 Processing temperature and time necessary to produce a safe food product are determined using inactivation kinetic parameters for a target microorganism. It is important to determine the inactivation parameters at conditions similar to processing conditions. Because most food processing is associated with thermal manipulation (either heating or cooling) of the materials, thermal characterization of foodborne microorganisms will lead to data that can be related directly to the processing protocols. Furthermore, the comparison of various final states as a function of various physical and chemical factors, starting from the same initial state, makes it possible to predict the effectiveness of methods to inactivate microorganisms. Differential scanning calorimetry (DSC) is used to characterize the thermally-induced changes in whole cells and ribosomes for L. plantarum and Escherichia coli and to evaluate the thermal inactivation kinetics of E. coli. The apparent enthalpy (DH) of E. coli was evaluated by a temperature scan in a DSC after pre-treatment in the calorimeter to temperatures between 56 and 80 oC. First order inactivation kinetics is combined with a linearly increasing temperature protocol. Viability of bacteria subsequent to a heat treatment between 56 and 80oC in the DSC is also determined by plate count. The fractional viability based on calorimetric and plate count data show a linear relationship. Viability loss and the irreversible change in DSC thermograms of pre-treated whole cells are highly correlated between 55 and 70oC. Comparison of DSC scans for isolated ribosomes shows that the thermal stability of ribosomes from E. coli is greater than the thermal stability of L. plantarum ribosomes, consistent with the greater thermal tolerance of E. coli observed from viability loss and DSC scans of whole cells. The calorimetric method provides accurate and reproducible kinetic parameters for inactivation in a shorter time with comparable accuracy to the plate count technique.
Session 33, Applications of calorimetry in food and biological materials
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