Desiccation

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).

1. Collected and Coordinated
By
Ahmed M. M. Mayla

2. ُنَسْحَأ ْنَمَوَّمِمالًْو
َ
ق ِإ اَعَد ْن ىَل
َص َلِ
م
َ
ع
َو ِالله
َ
قَو ااحِلاِ

ن
َّ
نِإ َلا ي
ِمِ
ل
ْ
س
ُ
م
ل
ا َنِمَن ي
{تل
ِّ
ص

ف:33}

3. َّسلا َنِم َلَز
ْ
تَأ َالله َّنَأ َر
َ
ت ْمَلَأ
ِ ب ا
َ
نْ جَر
ْ
خَأ
َ
ق اءاَم ِءاَمْلَأ ا
ا
فِل
َ
ن
ْ
خُم ٍتاَرَم
َ

ث ِه َنِمَو اَه
ُ
ناَو

َ
ن
ْ
خُم ٌرْمُحَو ٌض يِ ن ٌدَدُ ج ِلاَ نِ خلا يِ ناَر
َ
غَو اَه
ُ
ناَوْلَأ ٌفِل ٌدوُس ُب * ِسا
َّ
نلا َنِمَو
ٌفِل
َ
ن
ْ
خُم ِماَع
ْ
نَلأاَو ِّباَوَّدلاَوَ

ي
اَم
َّ
ثِإ َكِلَذَك ُه
ُ
باَوْلَأ

ا ِِِداَ نِِ ْنِم َالله
َ

َ
ْ
خُءاَمَلُع
رو

ف

غ ز تزغ الله نإ
{رطا

ق:27-28}

8. DESICCATION
•Gradual removal of water from cells by
manes of heating, salting, freezing….
•Leads to metabolic inhibition
•Not effective microbial control
•Many cells retain ability to grow when
water is reintroduced(Bacteriostatic)

9. MODE OF ACTION
•Microorganismscannotgroworreproducebutcan
remainviableforyears.
•whenwaterismadeavailabletothem,theycan
resumetheirgrowthanddivision.
•Thisabilityisusedinthelaboratorywhenmicrobesare
preservedbylyophilization,orfreeze-drying.
•Certainfoodsarealsofreeze-dried(forexample,coffee
andsomefruitadditivesfordrycereals).

10. CRYPTOBIOSIS
(ANHYDROBIOSIS)
•Cryptobiosisreferstothestateofan
organismthathasnodetectable
metabolicactivity,resultingfromextreme
andunfavorableenvironmentalconditions
•Anhydrobiosisreferstothestateof
survivingthelossof(almost)allbody
water.

11. DESICCATION TOLERANCE
•Desiccationtolerancerefersto
theabilityofanorganismto
withstandorendureextreme
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,…)

13. RESISTANCE AND DESICCATION
•Theresistanceofvegetativecellsto
desiccationvarieswiththespeciesand
theorganism'senvironment.For
example,thegonorrheabacterium(G-ve)
canwithstanddrynessforonlyaboutan
hour,buttuberculosisbacterium(G+ve)
canremainviableformonths.
•Moldsandyeastsmostresistant

14. •Virusesaregenerallyresistantto
desiccation,butnotasbacterialendospores,
someofwhichhavesurvivedforcenturies.
•Thisabilityofcertaindriedmicrobesand
endosporestoremainviableisimportantin
ahospitalsetting.Dust,clothing,bedding,
anddressingmightcontaininfectious
microbesindriedmucus,urine,pus,and
feces.

15. Mechanisms Of Desiccation Tolerance
•Theabilitytotoleratecompletedesiccationis
widespreadinorganismsthatareeither<5
mmlongorfoundmainlywheredesiccation-
sensitiveorganismsarescarce.Thissuggests
thatthereisatrade-offbetweendesiccation
toleranceandgrowth.

16. Mechanisms Of Desiccation Tolerance
•Recent molecular and biochemicalresearch shows
that organisms tolerate desiccation through aset of
mechanisms, including sugars that replace water and
proteins that stabilize macromolecules and
membranes,and anti-oxidants that counter damage
by reactive oxygen species.
•Theseprotections are often induced by drying, and
some of the genesinvolved may be homologous in
microbes, plants and animals.

17. APPARATUSES
•Dry heating, oven
(160ºC/2h,170ºC/1h), Dehydrator
•Freeze drying, lyophilizer
•Salting, desiccator,……….

18. DESICCATOR
•Itisaheavyglassorplasticcontainer
usedinpracticalchemistryformaking
orkeepingsmallamountsofmaterial
verydry.Thematerialisplacedona
shelf,andadryingagentordesiccant,
suchasdrysilicageloranhydrous
sodiumhydroxide,isplacedbelowthe
shelf.

19. DESICCATOR

20. HUMIDITY INDICATOR
•Oftensomesortofhumidityindicatoris
includedinthedesiccatortoshow,by
colorchanges,thelevelofhumidity.
Theseindicatorsareintheformof
indicatorplugsorindicatorcards.The
activechemicaliscobaltchloride(CoCl2).
Anhydrouscobaltchlorideisblue.Whenit
bondswithtwowatermolecules,
(CoCl2•2H2O),itturnspurple.Further
hydrationresultsinthepink
hexaaquacobalt(II)chloridecomplex
[Co(H2O)6]2+.

21. HUMIDITY INDICATOR

22. HUMIDITY INDICATOR

23. DEHYDRATORS
•Electric Dehydrator
•Brand Dehydrator

24. ELECTRIC DEHYDRATOR

25. BRAND DEHYDRATOR

26. BRAND DEHYDRATOR

27. LYOPHILIZER

28. LYOPHILIZER

29. DRYING
•Dryingcanbeusedtopreservefoods
becausetheabsenceofwaterinhibits
theactionofenzymes.Manyfoods,
includingpeas,beans,raisins,andother
fruits,areoftenpreservedbydrying.
Yeastusedinbakingalsocanbe
preservedbydrying.Endospores
presentsonsuchfoodscansurvive
drying,buttheydonotproducetoxins.

30. •Driedpepperonisausageandsmoked
fishretainenoughmoisturefor
microorganismtogrow.Because
smokedfishisnotcooked,eatingit
poisesariskofinfection.Sealingsuch
fishinplasticbagscreatesconditions
thatallowanaerobessuchas
Clostridiumbotulinumtogrow.

31. Clostridium botulinum

32. •Drying also naturally minimizes the spread o
infectious agents. Some bacteria, such as
Treponemapallidum, 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.

33. Treponemapallidum

34. FREEZE DRYING
•Freeze-drying,orlyophilization,isthe
dryingofamaterialfromthefrozen
state.Thisprocessisusedinthe
manufactureofsomebrandsofinstant
coffee;freeze-driedinstantcoffeehasa
morenaturalflavorthanotherkinds.
Microbiologistsuselyophilizationfor
long-termpreservationratherthan
destruction of cultures of
microorganisms.

35. •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
•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.
•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).
•Salting of foods does not protect against all potential
pathogens. Many fungi are halophilicas is
Staphylococcus aureus, a common source of bacterial
food poisoning.

37. Staphylococcus aureus

38. APPLICATIONS
•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

41. •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.