Faculty of Food Technology and Biotechnology, University of Zagreb
Food Technology and Biotechnology vol:43 issue:4 pages:321-327
A mathematical approach incorporating the shoulder effect during the quantification of microbial heat inactivation is being developed based on "the number of log cycles of reduction" concept. Hereto, the heat resistance of Escherichia coli K12 in BHI broth has been quantitatively determined in a generic and accurate way by defining the time t for x log reductions in the microbial population, i.e. t(xD), as a function of the treatment temperature T. Survival data of the examined microorganism are collected in a range of temperatures between 52-60.6 degrees C. Shoulder length S, and specific inactivation rate k(max) are derived from a mathematical expression that describes a non-log-linear behaviour. The temperature dependencies of S, and k(max) are used for structuring the t(xD)(T) function. Estimation of the t(xD)(7) parameters through a global identification procedure permits reliable predictions of the time to achieve a pre-decided microbial reduction. One of the parameters of the t(xD)(T) function is proposed as "the reference minimum temperature for inactivation". For the case study considered, a value of 51.80 degrees C (with a standard error, SE, of 3.47) was identified. Finally, the time to achieve commercial sterilization and pasteurization for the product at hand, i.e. BHI broth, was found to be 11.70 s (SE = 5.22), and 5.10 min (SE = 1.22), respectively. Accounting for the uncertainty (based on the 90 % confidence intervals, CI) a fail-safe treatment of these two processes takes 20.36 s and 7.12 min, respectively.