Lecture+17+thermaldestruction+and+water+activity+_color_

Lecture+17+thermaldestruction+and+water+activity+_color_ -...

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WATER ACTIVITY FST104 FEBRUARY 22, 2012 D value (time): Decimal reduction time Δ time resulting in a 10-fold change in viable cells Survival Curve Z value (temperature): Δ T resulting in a 10-fold change in D F value (time): D x number of logs reduction temperature log (D value) Z value Decimal Reduction Curve
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Below are survival data for Clostridium botulinum endospores held at 240°F. Graphically determine the D240°F for C. botulinum in this medium. Time Held (minutes) Number of Survivors 5 2.2 x 10^7 10 6.5 x 10^6 15 2.3 x 10^6 20 9.1 x 10^5 25 1.2 x 10^5 Practice problem #1 Answer: 10 minutes
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You have discovered a new pathogen in milk Given the following D values obtained for your new pathogen, determine the Z value using the semi-log graph paper. Indicate the Z value in correct units Temperature D value (in minutes) 50ºC 50 60ºC 14 70ºC 3.5 80ºC 0.9 Practice problem #2 The legal pasteurization for milk is 30 minutes at 63 °C. If you know that you will never need to kill more than 5 logs of your hypothetical new pathogen, is the current legal pasteurization procedure sufficient for safety? Definition: Process (minimum time and temperature) needed to destroy the most heat resistant pathogen or spoilage organism in the given food Pasteurization There is NO universal pasteurization process Not effective against spores Inactivates or kills 99 to 99.9% of spoilage microbes and enzymes
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Legal pasteurization of milk 30 min at 145 ºF (62.8 ºC) bulk 15 sec at 161 ºF (71.7 ºC) flash 1 -2 sec at 275 ºF (135 ºC) sterilization (Ultra-High Temperature, UHT) Milk Pasteurization The original target was
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Lecture+17+thermaldestruction+and+water+activity+_color_ -...

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