18Sterilization-2008 - Sterilization Why sterilize The...

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1 Sterilization Why sterilize The sterilization bioreaction Effect of scaling on sterilization Methods Why Sterilize? Sterility – NO living organisms Economic penalty is high for loss of sterility Contamination Vaccines must have only killed viruses Recombinant DNA fermentations - exit streams must be sterilized
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2 Sterilization Agents Thermal - preferred for economic large-scale sterilizations of liquids and equipment Chemical - preferred for heat-sensitive equipment ethylene oxide (gas) for equipment 70% ethanol-water (pH 2) for equipment/surfaces 3% sodium hypochlorite for equipment Radiation - UV for surfaces, x-rays for liquids (cost/safety) Filtration membrane filters have uniform micropores depth filters of glass wool Thermal Sterilization Heat susceptibility is organism dependent. Decimal reduction time (D Time) - Time to kill 90 % or 1 log unit of a population at a given temperature. Moist heat - Acts by denaturation and coagulation of proteins. To kill vegetative bacteria, yeast and mold -- 80º C for 5 -10 minutes; Mold spores -- 80º C for 30 minutes; Bacterial spores -- 121º C, 15 lbs/sq. in. pressure for at least 15 minutes.
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3 The Thermal Death Reaction Most frequently, the kinetic rate follows the Arrhenius rate theory: where k d is the specific death rate constant in minute -1 , A is the frequency factor in minute -1 . E d is the activation energy of death in Kcal/mole, R is the universal gas constant in Kcal/mole . K, and T is the absolute temperature (K). RT E d Ae k d - = Assume 1 st order rate constant where -dN/dt = k d N Substrate Product Transition State Reaction Coordinate G G : Gibbs energy Δ G Δ G o Gibbs Energy Change and Equilibrium constant Δ G = RT ln K; K = [X 1 ]/[X 2 ] R : Gas Constant, T : Absolute Temp [S ] = [S] exp ( −Δ G /RT ) Rate S Æ P ~ ν of bond breaking : vibrational frequency E = kT; E = h k : Boltzmann constant h : Planck constant = kT/h Reaction Rate = - d [S]/ dt = [S ] Transition State: Most unstable species on the reaction pathway -d [S]/ dt = [S ] = [S]( kT/h )exp ( −Δ G /RT )
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4 Activation Energy for Cells, Nutrients, and Enzymes Which one is more affected by raising temperature?
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18Sterilization-2008 - Sterilization Why sterilize The...

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