The Thermal Death Time Concept and Its Implications Revisited

Autor: Micha Peleg
Rok vydání: 2021
Předmět:
Zdroj: Food Engineering Reviews. 13:291-303
ISSN: 1866-7929
1866-7910
DOI: 10.1007/s12393-021-09279-8
Popis: Apart from actual incubation and/or testing, the mandated way to determine the microbial safety of thermally preserved foods is still anchored in the premise that the isothermal inactivation of bacterial cells and spore survival follows first-order kinetics. This is despite growing evidence to the contrary, and that the D value’s temperature-dependence too need not follow the log-linear model. Also, for technical reasons, the experimental detection level of survival ratios is usually four to six orders of magnitudes higher than that expected to assure a safe product. The theoretical implications of such a gap combined with non-linear inactivation kinetics are explored through simulations with especially constructed mathematical survival models. One of these models produces apparently log-linear or Weibullian survival patterns above the detection despite having a definite thermal death time, while the other has a substantial asymptotic residual survival level albeit below the detection level. The simulations highlight the notion that there is not enough information in an experimental survival curve’s shape to allow its continuation to below the detection level. Thus any thermal death time determined by extrapolation has no logical basis and can lead to either underestimation or overestimation of the thermal process’s lethality depending on the model chosen to describe it. The analysis lends support to the notion that safety factors and efficacy criteria in thermal processes should be based on observable survival ratios and not on log-linear kinetics.
Databáze: OpenAIRE
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