Thermal Death Kinetics

Thermal death of microorganisms at a particular temperature can be described by first-order kinetics  

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A test for viable spores should be included. Where spores are found, they should be tested for thermal death kinetics and, where the result indicates a compromise of sterility, the relevant batches discarded and the applied F0 increased until the absence of spores is confirmed. 

Death kinetics are obviously important in chemical or thermal sterilization. The spores formed by some bacteria are the hardest to kill. Problem 12.3 gives data for a representative case. 

Wang et al. report the death kinetics of Bacillus stearothermophilus spores using wet, thermal sterilization. Twenty minutes at 110°C reduces the viable count by a factor of lO". The activation temperature, E/Rg, is 34,200 K. How long will it take to deactivate by a factor of lO ... 

In this section, we discuss the kinetics of thermal cell death and sterilization. The rates of thermal death of most microorganisms and spores can be given by Equation 10.1, which is similar in form to the rate equation for the first-order chemical reaction, such as Equation 3.10. 

Design and operation of equipment for sterilizing media are based on the concept of thermal death of microorganisms. Consequently, an understanding of the kinetics of the death of microorganisms is important to the rational design of sterilizers. 

V. Damjanovic, Kinetics of thermal death and prediction of the stabilities of freeze-dried streptomycin-dependent live Shigella vaccines. J. Biol. Stand. 2 297-311, 1974. 

Moats, W.A. 1971. Kinetics of thermal death of bacteria. Journal of Bacteriology 105 165-171. 

A very useful application of dummy or indicator variable regression is in modeling regression functions that are nonlinear. For example, in steam sterilization death kinetic calculations, the thermal death curve for bacterial spores often looks sigmoidal (Figure 9.9). 

These same kinetic methods of thermal death rates can also be applied to predict the time for detecting a flavor change in a food product. Dietrich et al. (Dl) determined a curve for the number of days to detect a flavor change of frozen spinach versus temperature of storage, i he data followed Eq. (9.12-8) and a first-order kinetic relation. 

The inactivation rate constants at reference temperature To and pressure po are given by kr and kj, , respectively. is the activation energy and is the activation volume, both derived from the corresponding slopes of the semilogarithmic plots [2j. Alternatively, for the first-order kinetics, the thermal death time and pressure death time approach can be applied (compare with Eq. (9.8)) with Dr and respectively being the decimal reduction times at reference temperature and pressure [2,46—48]. 

Inactivation, regarding thermal treatment, is based on the assumption that death of microorganisms versus time is linear in a semi logarithmic graph. Thus, inactivation by HP usually uses the kinetic concepts of thermal treatment D (decimal reduction time time in minutes required to inactivate... 

As with sterilization by saturated steam, thermal damage to biological systems as a result of dry heat sterilization processes is a function of absorbtion of heat energy. Inactivation of microorganisms is by oxidation. The kinetics of oxidation and population death approximate to first-order reactions, but they are significantly different from the processes of coagulation of cellular proteins found with moist heat sterilization in that they require far higher temperatures and proceed more slowly. 

Thermal processing is used to cause the death of various undesirable microorganisms, but it also causes undesirable effects, such as the reduction of certain nutritional values. Ascorbic acid (vitamin Q and thiamin and riboflavin (vitamins B, and B ) are partially destroyed by thermal processing. The reduction of these desirable constituents can also be given kinetic parameters such as Fq and z values in the same way as for sterilization and pasteurization. Examples and data are given by Charm (C2). 

In this chapter we formulate the thermodynamic and stochastic theory of the simple transport phenomena diffusion, thermal conduction and viscous ffow (1) to present results parallel to those listed in points 1-7, Sect. 8.1, for chemical kinetics. We still assume local equilibrium with respect to translational and internal degrees of freedom. We do not assume conditions close to chemical or hydrodynamic equilibrium. For chemical reactions and diffusion the macroscopic equations for a given reaction mechanism provide sufficient detail, the fluxes in the forward and reverse direction, to write a birth-death master equation with a stationary solution given in terms of For thermal conduction and viscous flow we derive the excess work and then find Fokker-Planck equations with stationary solutions given in terms of that excess work. 

Trauma is by definition an injury produced by a force (violence, thermal, chemical, or an extrinsic agent). Occupational trauma transpires from the contact with or the unplanned release of varied sources of energy intrinsic within the workplace. Most workplaces have a plethora of energy sources from potential (stored) energy to kinetic (energy in motion) energy sources. These sources may be stacked materials (potential) or a jackhammer (kinetic). The sources of energy are the primary causes of trauma deaths and injuries to workers. 

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