88D-23 |
Calorimetric determination of microbial survival curve of Escherichia coli |
J. LEE, Food Science and Technology, The Ohio State University, 590 Woody Hayes Dr., Columbus, OH 43210 and G. Kaletunç, Food, Agricultural, and Biological Engineering, The Ohio State University. Processing temperature and time necessary to produce a safe product are determined using D and z values for a target microorganism. D and z values of microorganisms are calculated from the survival curves produced at several temperatures. In industry, processing temperature can not be reached instantly but requires a come up time. It is important to determine the D and z values at conditions similar to processing conditions. Objective of the investigation is to determine the D and z values of Escherichia coli K12 using calorimetric data and to compare them with plate count data. Pellets of centrifuged E. coli K12 are heated in differential scanning calorimeter (DSC) at 3 oC min-1. Samples are pre-heated in the DSC to 60, 62.5, 65, 70, 75, and 80 oC. The apparent enthalpy and the reversibility of thermal transitions are evaluated by two consecutive scans from 1 oC to 150 oC. The enthalpy corresponding to the endothermic peak area between 48 and 125 oC is calculated from the DSC curves. Loss of viability subsequent to heat pre-treatment in DSC is determined by plate count. Conventional semi-logarithmic survival curve analysis is combined with a linearly increasing temperature protocol to calculate z and D values from both calorimetric and plate count data. D and z values are determined from ln(-ln(N/N0) vs. temperature and ln(-ln((DH-DHf)/(DHo-DHf)) vs. temperature curves, where “f” indicates maximally treated cells and “o” untreated cells. Temperatures for 1 through 12-log microbial reductions, calculated from plate count and enthalpy data are in agreement within approximately 1 oC. Enthalpy data obtained from DSC can predict D and z values, and the linear temperature rise to reduce the microbial count by a chosen factor in a shorter time with comparable accuracy to the plate count technique.
Session 88D, Food Microbiology: General
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