1. The Control of Microbial Growth

2. Physical and Chemical Control of Microbes
Chapter 7 2

3. to destroy or reduce microbes
Control of microbes
Physical and chemical methods
to destroy or reduce microbes
in a given area 3

4. 4

5. STERILIZATION All killed non-selective Microbial death
Involves permanent loss of reproductive capability, even under optimum growth conditions 5 5 5

6. Mode of action of Microbial control agents
Alteration of membrane permeability
( lipid & proteins)
Damage to proteins and Nucleic acids
(cellular proteins & DNA replication) 6

7. Physical Methods of Control
Heat
Filtration
Radiation

8. Physical Methods of Control HEAT
Mode of action: Denaturing proteins. 8

9. HEAT Mode of action: Denaturing proteins
Moist heat
Dry heat
Denaturation of proteins
Oxidation or coagulation of proteins
Flaming
Boiling = 100C
Pasteurization less than 100C
Hot air oven
Autoclaving more than 100C

10. Physical Methods of Control HEAT
Moist heat (Kills by denaturation of proteins)
= boiling
= pasteurization
= autoclaving (Steam under pressure)
Dry heat = flaming
= hot air oven

11. Pasteurization Eliminate pathogenic microbes
Lowering microbial count and prolong shelf life. without altering the flavor
(HTST) High temperature at short time
140 oC for 3 second (dairy products) store several month without refrigeration
63  C for 30 minutes ordinary
72  C for 15sec HTST
UHT Ultra high temperature, 11

12. Steam under pressure Autoclaving
The higher the pressure the higher the temperature15 min at 121 C at 15 psi 12

13. Dry heat using higher temperatures than moist heat, can also sterilize
Flaming ( oxidation)
Dry ovens – oC- 2 hours
(coagulate proteins & oxidation) 13

14. Using Heat to Control Microbes14

15. Filtration Is the passage of liquid
or gas through filters with pores small enough
to retain bacteria
Membrane filters 15

16. Membrane filters
pores
bacteria 16 16 16 16

17. Radiation
Effect on cells varies according to its wavelength, duration and intensity.
Ionizing and non ionizing radiation.
Ionizing radiation:
Gamma rays: x-rays & high –energy electron beams = has a high degree of penetration
used to sterilize medical supplies & food products
Non-ionizing radiation
- little penetrating power to sterilize air, water & solid surfaces
UV light which interfere with DNA replication 17

18. RADIATION EFFECT Oxidation of DNA effect of ionizing radiation
Interferes with DNA replication 18

19. 19

20. Chemical control
Chemical agents that used on living tissues as antiseptics
And on non living objects as disinfectants
Halogens
Phenolics
Chlorhexidine
Alcohols
Hydrogen peroxide
Detergents & soaps
Heavy metals
Aldehydes 20

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