Microorganisms cannot grow or reproduce but can remain viable for years.
when water is made available to them, they can resume their growth and division.
This ability is used in the laboratory when microbes are preserved by lyophilization, or freeze-drying.
Certain foods are also freeze-dried (for example, coffee and some fruit additives for dry cereals).
Microorganisms cannot grow or reproduce but can remain viable for years.
when water is made available to them, they can resume their growth and division.
This ability is used in the laboratory when microbes are preserved by lyophilization, or freeze-drying.
Certain foods are also freeze-dried (for example, coffee and some fruit additives for dry cereals).
Microorganisms cannot grow or reproduce but can remain viable for years.
when water is made available to them, they can resume their growth and division.
This ability is used in the laboratory when microbes are preserved by lyophilization, or freeze-drying.
Certain foods are also freeze-dried (for example, coffee and some fruit additives for dry cereals).
Microorganisms cannot grow or reproduce but can remain viable for years.
when water is made available to them, they can resume their growth and division.
This ability is used in the laboratory when microbes are preserved by lyophilization, or freeze-drying.
Certain foods are also freeze-dried (for example, coffee and some fruit additives for dry cereals).
8. DESICCATION
โข Gradual removal of water from cells by
manes of heating, salting, freezingโฆ.
โข Leads to metabolic inhibition
โข Not effective microbial control
โข Many cells retain ability to grow when
water is reintroduced(Bacteriostatic)
9. MODE OF ACTION
โข Microorganisms cannot grow or reproduce but can
remain viable for years.
โข when water is made available to them, they can
resume their growth and division.
โข This ability is used in the laboratory when microbes are
preserved by lyophilization, or freeze-drying.
โข Certain foods are also freeze-dried (for example, coffee
and some fruit additives for dry cereals).
10. CRYPTOBIOSIS
(ANHYDROBIOSIS)
โข Cryptobiosis refers to the state of an
organism that has no detectable
metabolic activity, resulting from extreme
and unfavorable environmental conditions
โข Anhydrobiosis refers to the state of
surviving the loss of (almost) all body
water.
11. DESICCATION TOLERANCE
โข Desiccation tolerance refers to
the ability of an organism to
withstand or endure extreme
dryness, or drought-like
conditions.
12. FACTORS
1. Kind of organism:
2. Type of desiccant (material on which
the microorganisms are dried)
3. Physical conditions(T, light , P,โฆ)
13. RESISTANCE AND DESICCATION
โข The resistance of vegetative cells to
desiccation varies with the species and
the organism's environment. For
example, the gonorrhea bacterium(G-ve)
can withstand dryness for only about an
hour, but tuberculosis bacterium(G+ve)
can remain viable for months.
โข Molds and yeasts most resistant
14. โข Viruses are generally resistant to
desiccation, but not as bacterial endospores,
some of which have survived for centuries.
โข This ability of certain dried microbes and
endospores to remain viable is important in
a hospital setting. Dust, clothing, bedding,
and dressing might contain infectious
microbes in dried mucus, urine, pus, and
feces.
15. Mechanisms Of Desiccation Tolerance
โข The ability to tolerate complete desiccation is
widespread in organisms that are either <5
mm long or found mainly where desiccation-
sensitive organisms are scarce. This suggests
that there is a trade-off between desiccation
tolerance and growth.
16. Mechanisms Of Desiccation Tolerance
โข Recent molecular and biochemical research shows
that organisms tolerate desiccation through a set of
mechanisms, including sugars that replace water and
proteins that stabilize macromolecules and
membranes, and anti-oxidants that counter damage
by reactive oxygen species.
โข These protections are often induced by drying, and
some of the genes involved may be homologous in
microbes, plants and animals.
18. DESICCATOR
โข It is a heavy glass or plastic container
used in practical chemistry for making
or keeping small amounts of material
very dry. The material is placed on a
shelf, and a drying agent or desiccant,
such as dry silica gel or anhydrous
sodium hydroxide, is placed below the
shelf.
20. HUMIDITY INDICATOR
โข Often some sort of humidity indicator is
included in the desiccator to show, by
color changes, the level of humidity.
These indicators are in the form of
indicator plugs or indicator cards. The
active chemical is cobalt chloride (CoCl2).
Anhydrous cobalt chloride is blue. When it
bonds with two water molecules,
(CoCl2โข2H2O), it turns purple. Further
hydration results in the pink
hexaaquacobalt(II) chloride complex
[Co(H2O)6]2+.
29. DRYING
โข Drying can be used to preserve foods
because the absence of water inhibits
the action of enzymes. Many foods,
including peas, beans, raisins, and other
fruits, are often preserved by drying.
Yeast used in baking also can be
preserved by drying. Endospores
presents on such foods can survive
drying, but they do not produce toxins.
30. โข Dried pepperoni sausage and smoked
fish retain enough moisture for
microorganism to grow. Because
smoked fish is not cooked, eating it
poises a risk of infection. Sealing such
fish in plastic bags creates conditions
that allow anaerobes such as
Clostridium botulinum to grow.
32. โข Drying also naturally minimizes the spread o
infectious agents. Some bacteria, such as
Treponema pallidum, which causes syphilis,
are extremely sensitive to drying and die
almost immediately on a dry surface; thus
they can be prevented from spreading by
keeping toilet seats and other bathroom
fixtures dry. Drying of laundry in dryers or in
the sunshine also destroys pathogens.
34. FREEZE DRYING
โข Freeze-drying, or lyophilization, is the
drying of a material from the frozen
state. This process is used in the
manufacture of some brands of instant
coffee; freeze-dried instant coffee has a
more natural flavor than other kinds.
Microbiologists use lyophilization for
long-term preservation rather than
destruction of cultures of
microorganisms.
35. โข Organisms are rapidly frozen in alcohol
and dry ice or in liquid nitrogen and are
then subjected to a high vacuum to
remove all the water while in the frozen
state. Rapid freezing allows only very
tiny ice crystal to form in cells, so the
organisms survive this process.
Organism so treated can be kept alive
for years, store under vacuum in the
freeze-dried state
36. APPLICATIONS
โข Desiccation of microbes is a very useful means of food
preservation and to control the growth of spoilage
germs and pathogens. Foods that have a high water
activity are most subject to spoilage and typically must
be refrigerated or frozen.
โข Numerous foods are preserved by adding salt or sugar
to decrease the water activity of the foods. This process
creates hypertonic conditions and causes water to leave
bacterial cells (plasmolyze).
โข Salting of foods does not protect against all potential
pathogens. Many fungi are halophilic as is
Staphylococcus aureus, a common source of bacterial
food poisoning.
38. APPLICATIONS
โข Dehydrated foods are perfect for
backpacking and camping because they
are lightweight and store long-term
without refrigeration. They can be
eaten as is or rehydrated in water over
a campfire for a warm meal
39.
40.
41. โข Freeze dried food is easy to prepare in
an emergency situation or backpacking.
Save money by buying Mountain House
freeze dried food at case pricing.
