The document discusses various physical methods of microbial control including heat, filtration, low temperatures, and radiation. It describes how heat can be used to kill microorganisms through processes like boiling, autoclaving, pasteurization, and dry heat sterilization. Filtration is also discussed as a way to remove microorganisms using membrane filters or HEPA filters. Specific temperatures, times, and pore sizes required to effectively kill or remove various microbes are provided.

1. Physical Methods of
Microbial Control:
Heat and Filtration
By: SARIPADA, Jadidah D.

2. Physical Methods of Microbial Control
• Heat
• Filtration
• Low Temperatures
• High Pressure
• Desiccation
• Osmotic Pressure
• Radiation

3. A. Heat
- It is one of the most common methods of food
preservation.
- It is also usually used to sterilize laboratory media and
glassware and hospital instruments.
- Appears to kill microorganisms by denaturing their
enzymes.

4. Thermal death point (TDP)
- It is the lowest temperature at which all the
microorganisms in a particular liquid suspension will be
killed in 10 minutes.
Thermal death time (TDT)
- It is the minimal length of time for all bacteria in a
particular liquid culture to be killed at a given temperature.
Decimal reduction time (DRT or D value)
- It is the time, in minutes, in which 90% of a population of
bacteria at a given temperature will be killed .

5.  Moist Heat
- It kills microorganisms primarily by the coagulation of
proteins, which is caused by breakage of the hydrogen
bonds that hold the proteins in their three-dimensional
structure.

6. Boiling
- It kills vegetative forms of bacterial pathogens, almost all
viruses, and fungi and their spores within about 10
minutes.
- Endospores and viruses are not killed this easily.
- Not always a reliable sterilization procedure.

7. Autoclaving
- It is the preferred
method of
sterilization, unless
the material to be
sterilized can be
damaged by heat or
moisture.
- Retorts are large
autoclaves
The Relationship Between the Pressure and
Temperature of Steam at Sea level
Pressure (psi in excess of
atmospheric pressure
Temperature (ºC)
0 psi 100
5 psi 110
10 psi 116
15 psi 121
20 psi 126
30 psi 135

8. The Effect of Container Size on Autoclave Sterilization Times
for Liquid Solutions
Container Size Liquid Volume Sterilization Time (min)
Test tube:
18 x 150 nm
10 ml 15
Erlenmeyer flask:
125 ml
95 ml 15
Erlenmeyer flask:
2000 ml
1500 ml 30
Fermentation bottle:
9000 ml
6750 ml 70

9. Several methods that can indicate whether sterilization
has been achieved:
• Heat-sensitive autoclave tape- It has white stripes that
turn black when the appropriate temperature is achieved
during a successful autoclave run.
• Diack tube- It is a glass ampule containing a
temperature-sensitive pellet that melts at the proper
sterilization temperature.
• Biological indicator spore test- It uses either a strip of
paper or liquid suspension of the endospore Geobacillus
stearothermophilus to determine whether the endospores
are killed by the process.

11.  Pasteurization
- Developed by Louis Pasteur in
the 1860s.
- It is a heat-treatment process
that destroys pathogenic
microorganisms in certain foods
and beverages.
- The dairy industry routinely uses
a test to determine whether
products have been pasteurized:
the phosphatase test.

12. High-temperature short-time (HTST) pasteurization
- It is applied as the milk flows continuously past a heat exchanger.
- It lowers total bacterial counts, so the milk keeps well under
refrigeration.
Ultra-high-temperature (UHT) treatments
- Despite being left out of the refrigerator, UHT milk sometimes
lasts 6 to 9 months.
- To avoid giving the milk a cooked taste, a UHT system is
used.

14. Equivalent treatments
- As the temperature is increased, much less time is
needed to kill the same number of microbes.

15.  Dry Heat Sterilization
- It kills by oxidation effects.
- It kills bacteria, viruses, and fungal spores without
leaving any residue behind.

16. Hot-air sterilization
- Items to be sterilized by this procedure are placed in an
oven.
- Generally, a temperature of about 170°C maintained for
nearly 2 hours ensures sterilization.
Direct flaming
- To effectively sterilize the inoculating loop, you heat the
wire to a red glow.
- A similar principle is used in incineration.

17. B. Filtration
- It is the passage of a liquid or
gas through a screen like
material with pores small enough
to retain microorganisms
- It is used to sterilize heat-
sensitive materials, such as
some culture media, enzymes,
vaccines, and antibiotic
solutions.

18. Membrane filters
- Composed of such substances as cellulose esters or
plastic polymers, have become popular for industrial and
laboratory use.
- These filters are only 0.1mm thick.
- Pores are 0.22 μm and 0.45 μm sizes.
High-efficiency particulate air (HEPA) filters
- Remove almost all microorganisms larger than about 0.3
μm in diameter.
- Filterable viruses are unseen pathogens that pass
through the filters.

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