Chapter 11

Chapter 11 - Chapter11 PhysicalandChemicalControlofMicrobes

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Chapter 11 Physical and Chemical Control of Microbes Control of Microbial Growth 0 *Purpose: stop spreading the diseases or food spoilage 1 Methods 0 Physical Agents 0 •Heat 0 -Moist heat and dry heat 1 -Mechanism - denaturing the enzymes 2 -Most commonly used method of killing the microbes 3 - Thermal Death Point  0 -The lost temp at which all the microbes are killed in 10  min 4 - Thermal Death Time 0 -The minimal length of time needed to kill all bacteria at  given temperature 5 Moist heat     0 -Mechanism: coagulation of proteins 1 -Boiling (100 C) for 10 minutes kills vegetative cells of  2 -Hepatitis virus can survive up to 30 min. of boiling; some  bacterial spores can survive more than 20 Hrs. 3 -Tyndalization - boiling the medium for 60 min. repeatedly  for 3 days 4 5 Autoclaves - steam under pressure     0 -Provide high temp. and high pressure (pressure: 1  atm, temp.: 121 C) 1 -All microbes are killed in 15 minutes 2 -Steam should contact all surfaces 3 -Time is different for longer volumes 4 -Used for sterilization of: 0 Culture media 1 Equipment 2 Biological waste
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5 More efficient than ovens 6 Pasteurization     0 Original pasteurization: 63 C for 30 min. 1 Today pasteurization - high temperature short-time  pasteurization: 72 C for 15 sec. or 2 Ultra-High-Temperature Pasteurization 0 7 8 Dry Heat Sterilization     0 mechanism: oxidation 1 flaming - inoculating loops 2 hot-air sterilization 0 oven - 170 C for 2 hr. What is more efficient? Dry or Moist heat? Moist because of the shortness of  time 9 Desiccation     0 in the absence of water microbes cannot grow but cannot  survive 1 bacterial spores can survive for centuries 2 Survival depends on microbial type and organism’s  environment (embedded in mucus - better survival) 10 11 Low Temperatures     0 Effect depends o the microbial type 1 Ordinary refrigeration (0 - 7 C) - bacteriostatic effect 0 Slows down growth, stops growth but does not kill
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This note was uploaded on 09/16/2011 for the course MCB 2000 taught by Professor Gantar during the Fall '08 term at FIU.

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Chapter 11 - Chapter11 PhysicalandChemicalControlofMicrobes

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