Food Preservation .

FOOD PRESERVATION
BY
MRS.P.HEPZIBAH ARULMANI
TUTOR
SRMTCON

DEFINITION
It can be defined as the science that deals with
the process of the prevention of decay or spoilage of
food, thus allowing it to be stored in a fit condition
for future use.
Preservation of food increases the self life of foods
and thus ultimately ensures its supply during times of
scarcity and natural drought.

FOOD SPOILAGE
Food spoilage is a state in which food is deprived of
its good or effective qualities.Deterioation or spoilage
starts from the time food is harvested, slaughtered or
manufactured and results in undesirable changes in
the physical and chemical characteristics of food.

CAUSES OF FOOD SPOILAGE
• Growth and activity of microorganisms such as
bacteria, yeast and moulds.
• Activities of food enzymes and other chemical reactions
within the food.
• Non-enzymatic reactions in food such as oxidation and
mechanical damage.
• Inappropriate temperatures for a given food.
• Gain or loss of moisture
• Reaction with oxygen and light.
• Insects and rodents.

NEED FOR PRESERVATION
• To increase the shelf 1ife of foods.
• To prepare new products like jams, papads, pickles, etc.
Such products are enjoyed by everyone and all the year
round.
• Processing reduces the bulk of fruits and vegetables.
The storage and transportation becomes easier
• Helps in utilizing the food stuffs when available in
excess.

PRINCIPLE OF FOOD PRESERVATION
• Preservation or delay of microbial decomposition:
That is archived by :
• Keeping out microorganisms (asepsis)
• Removal of microorganisms,i.e., by filtration
• Hindering the growth of activity of
microorganisms,i.e., by low temperature, drying,
anaerobic conditions, &
• Killing the microorganisms,i.e., by heat or radiations.

Cont;
• Preservation or delay by self – decomposition of
food. This is brought about by :
• Destruction or inactivation of food enzymes i.e, by
blanching&
• Preservation or delay of chemical reactions i.e,
preservation of oxidation by means of an antioxidant.
• Preservation of damage caused by insects, animals &
mechanical causes.

METHODS OF FOOD PRESERVATION
Salting of meat, fish and vegetables was the oldest method of
preservation. Pickling in salt and vinegar, sun drying and
preserving of fruits and vegetables in sugar and honey are
among the other methods.
Foods can also be preserved by freezing. By removing the
cause of food spoilage, foods can be preserved. When growth
of microorganism is only retarded, preservation is temporary.
When spoilage organisms are completely destroyed, a more
permanent preservation is achieved.

Cont;
The discovery of canning as a standard technique of
preserving foods in sealed containers subject to high
temperature was established in 1810 by Nicholas
Appert. ]
Around 1860,Louis Pasteur discovered that microbes
were the main cause of spoilage and introduced a heat
treatment known as pasteurisation to the world.

BY PREVENTING FOOD CONTAMINATION
(ASEPSIS)
• Process of preventing contamination of food by spoilage
micro-organisms is called asepsis.
• Inner tissue of healthy animal and plants do not contain
micro-organisms and if present they usually do not spoil
food.
• Therefore, microbial decomposition of food can be
prevented by preventing contamination of food by
spoilage organisms.
• Several foods like egg contains natural covering around
food that prevent entry of spoilage organism into the
food.

Cont;
• Nowadays, variety of such artificial barrier are made
around the food to prevent contamination.
• For.eg. fruits and vegetables are stored for years by
coating the wax around them.
• Some other artificial barriers that prevent the
contamination includes wrappers, cartoons and cans.
• Safe handling of food and good personal hygiene of
food handler are important method to prevent or
minimize contamination of food by spoilage organisms.
• Most spoilage micro-organisms enter into the food by
contamination from external sources like water, air etc.

BY REMOVING MICROORGANISMS FROM
CONTAMINATED FOOD
• It is second level of preservation of microbial
decomposition of food.
• If contamination of food by spoilage organism is not
prevented, spoilage of food still can be prevented by
removing contaminated micro-organisms from the
food.
• Some techniques that preserve food by removing
micro-organisms include:

FILTRATION:
• It is only one successful method for removing micro-
organisms from contaminated food.
• Unfortunately, this method is applicable only for clear
liquid like clear fruit juice, beverages etc.
• To remove micro-organisms, liquid food is filtered
through sterile bacterial filter.

CENTRIFUGATION /SEDIMENTATION:
• Centrifugation removes some but not all micro-
organisms from contaminated liquid food.
• When liquid food is centrifuged suspended particle,
debris and some micro-organisms settle to the bottom
which is later separated and remove from the food.
• This technique is commonly used for milk in dairy
industries.

WASHING:
• This method is commonly used for vegetable and fruits.
Dusts and micro-organisms present on the surface of whole
vegetable and fruits are removed by washing with sterile
water.
• One limitation of washing is that it increases water activity
of some food and hence facilitates growth of remaining
spoilage organisms.
• Further more, if washing water is not sterile, it adds
spoilage organisms in food.

Cont;
TRIMMING:
• Trimming is the process of removing spoiled parts of
food like vegetables and fruits by cutting.
• Trimming prevents spread of micro-organisms from
spoiled part into inner healthy tissue.

BY INHIBITING OR KILLING
MICROORGANISMS
Different methods that preserve food either by killing
micro-organisms or by slowing down their growth
and activity includes:
– Preservation of High temperature (Heat)
– Preservation by low temperature
– Preservation by Drying
– Preservation by Radiation (irradiation)
– Chemical agents used in preservation of food

Preservation of food by High temperature (Heat):
• Heat is the most commonly used method of food
preservation.
• Heat kills spoilage of micro-organisms by denaturation
of cytoplasmic protein and enzyme.
• Two types of heat i.e. dry heat and moist heat are used in
preservation of food.
• Moist heat is more effective in killing micro-organisms
than dry heat.
• Heat causes denaturation of protein and enzyme by
breaking down their bonds.
• Breaking of bond occurs by two mechanisms i.e.
hydrolysis and oxidation.

Cont;
• Hydrolysis require water but oxidation does not.
• Hydrolysis require less energy (heat) for breaking of
bond than oxidation.
• Therefore, if moisture is present in food, bonds of
protein and enzymes are broken down by hydrolysis
even at lower temperature.
• This is the reason why moist heat can kill micro-
organisms completely at condition of 121.5oC for 15
min but dry heat requires 160oC for 1-2hrs to kill the
same organisms.
• Various factors affect killing of micro-organisms in
food by heat.

Cont;
Some such factors include:
 Time-temperature relationship
 Density of micro-organisms in food, if density is high,
higher temperature is needed.
 Types of micro-organisms present in food, e.g. Spore are
difficult to kill than vegetative cells
 Growth stage of micro-organisms, e.g. micro-organisms
present in log phase are easily killed but micro-
organisms present in late log phase and stationary phase
are somewhat heat resistant.

Cont;
 Micro-organisms in dry food are difficult to kill than
in moist food.
 If food is acidic or alkaline, micro-organisms present
in log phase are easily killed by heat. On the other
hand, if food is neutral, high temperature is needed to
kill the same organisms.
 Penetration of heat into inner layer of food also
affects killing of micro-organisms.

DIFFERENCE BETWEEN DRYHEAT AND
MOIST HEAT
DRY HEAT
• It is less effective in killing
micro-organisms.
• It damages protein and enzyme
by oxidation.
• It is especially valuable to
sterilize the food whose quality
is damaged by moisture (e.g.
flour) and for lipids foods.
• Dry heat is applied to the food
by spraying moisture free
heated air over the food and by
hot air oven.
• Conditions for sterilization is
160oC for 1-2 hrs.
MOIST HEAT
• It is more effective in killing
micro-organisms
• It damages protein and enzyme
by hydrolysis or coagulation.
• Moisture cannot penetrate into
hydrophilic lipid food and
moisture damage the quality of
powder foods like flour.
• Moist heat can be applied by
boiling the food in water or by
spraying heated steam over the
food.
• Conditions for sterilization is
121.5oC for 15 minutes.

Cont;
Some technique of food penetration by heat includes:
PASTEURIZATION:
• Pasteurization is a selective or gentle heating technique
originally developed by Lewis Pasteur for milk and
milk products.
• Nowadays, pasteurization is also used for preservation
of other beverages like beer, fruit juice etc.
• Pasteurization is a selective heating technique and it
kills some but not all micro-organisms present in milk.
• If milk is contaminated by some disease causing
micro-organisms, milk cannot be heated at boiling
temperature to kill these micro-organisms.

Cont;
• It is because heating at high temperature brings several
undesirable changes in milk. E.g. it kills beneficial lactic
acid bacteria present in milk.
• Similarly, casein protein precipitate, lactose caramelizes,
flavor of milk changes.
• Such milk becomes unsuitable for production of milk
products like ice cream, cheese.
• Similarly, beverages like beer and fruit juice cannot be
heated at higher temperature because it brings several
undesirable changes in flavor, taste etc.

Cont;
• In pasteurization, milk and beverages are heated at lower
temperature that kills spoilage or pathogenic organisms
without bringing undesirable changes in the product.
• There are three techniques of pasteurization of milk which
differ in their time-temperature relationship.
• Time-temperature relation of pasteurization are selected on
the basis of three bacteria which are transmitted through
milk (Mycobacterium bovis, Coxiella buretii and Brucella
abortus).

Cont;
• Low temperature holding (LTH) or Vat pasteurization:
– In this method, milk is heated at 62.8oC for 30
minutes.
• High temperature short time (HTST) method:
– In this method, milk is heated at 71.7oC for 15
seconds.
• Ultra-pasteurization:
– In this method, milk is heated at about 137.8oC for 2
seconds.

CANNING:
• Canning is the process of preservation of food by keeping
them in sealed container and then heating the container.
• Canning techniques was originally developed by Nicoles
Appert.
• There are two types of canned food i.e. heated and
unheated canned food.
• During canning at first raw food is washed and then
processed.
• Then processed food is placed into a suitable can and the
can is then heated.
• Sealed cans can be heated either by immersing it into
boiling water or by spray of super-heated steam or heated
dry air. -Cont;

There are two system of canning,
– i.e. hot pack system and cold pack system.
• In hot pack system, raw food is preheated before
packing into the can and in cold pack system, food is
not preheated.
• Canning is commonly used for preservation of many
foods like vegetable, meat, fish etc.
• Canned food is microbiologically more stable and
remain unspoiled for long time.

Cont;
• It is because any micro-organism present in raw food are
killed during heating the can and sealed container prevents
entry of spoilage organism into the food.
• Defective canning is not safe for preservation of food.
For.eg. if canned food is not properly heated, some
thermophilic organism and endospore of bacteria present in
raw food are not killed.
• Such spores then germinate and cause spoilage of the food
even if the can is intact.

Cont;
• Further more, can must be completely filled with food.
• If any space or air is present inside the can, this aerobic
condition facilitates germination of surviving spores.
• Similarly, can used for packaging the food must be
completely sealed.
• If any breaks or leaks are present in can many spoilage
organisms enter into the food and spoil the food.
• Furthermore, air enters into the can through leaks that
facilitates germination of surviving spores.

Cont;
BLANCHING OR SCALDING:
• Blanching is the process of washing vegetables or fruits
in warm water before storage.
• Advantages of blanching includes:
– It inactivates enzyme of food that cause self-
decomposition.
– It reduces number of micro-organisms present on the
surface of food.
– It brings wilting of leafy vegetables and helps in
packaging.
– It enhances fixing of intense green color of fruits
and vegetables.

Cont;
ROASTING:
• It is used for meat and meat products.
• During roasting internal temperature of meat reaches
(80-85)o C.
BAKING:
• It is used for bread, cake and other bakery products.
• During baking temperature maximum of 97oC is
reached.
FRYING:
• It is used for vegetable, meat, fish etc.
• During frying outer surface of food becomes very hot
but internal temperature of food never exceed 100oC.

Cont;
COOKING:
• During cooking temperature around 100oC is reached.
SIMMERING:
• It is the process of gentle boiling of food with the
temperature of about 100oC.
Preservation of food by low temperature:
• Low temperature is commonly used physical method of
preservation of food.
• Low temperature preserves food by:
– Slowing down growth and activity of spoilage organism
in food.
– By slowing down the rate of chemical reaction or other
enzymatic activity that cause self-decomposition of food.
– Sometimes low temperature kills spoilage organism in
food. E.g. in case of deep freezing.

Cont;
Different methods of food preservation by low temperature
Common or cellar storage:
• Common storage is the technique of preservation of certain
foods like potato, onion etc. in home by spreading them in
cold room.
• In common storage, storage temperature is slightly lower
than that of outside air.
• But this technique food is not stored for long time but it is
still used where cold storage and facilities are not available.

Chilling or cold storage:
• In chilling or cold storage, storage temperature is
usually between (0-10)oC.
• At this temperature, growth and activity of most bacteria
except psychrophiles is significantly slowed down.
• Therefore, by chilling storage, food can be stored for
long time than common storage.
• However, if psychrophilic organisms are present in food,
they grow in food and cause spoilage.

Cont:
• Selection of appropriate temperature is very important
because quality of some food is damaged at lower
temperature storage temperature of some food are (10-
12.8)o C for sweet potato, (13.3-16.7)o C for banana
etc.
• This method is most commonly used for short term
storage of highly perishable foods like meat, milk, fish
etc.
• Fish is stored by placing it in cold ice.

Freezing or frozen storage:
• In freezing storage, storage temperature is between (-15
to -29)oC.
• At this temperature, growth of even psychrophilic
bacteria is completely inhibited.
• Therefore, food kept in frozen storage remain fresh in
long time without undergoing microbial decomposition.
• Furthermore, self-decomposition of food occurs very
rarely or not at all at this temperature.
• Sometimes, freezing also kills spoilage organisms
present in food.
• Therefore, frozen storage is very effective method of
food preservation among these three techniques.

Cont;
• Killing mechanism of freezing is due to formation of
ice-crystal and dehydration of microbial cell.
• When food is frozen, surrounding water freezes to
form ice-crystals.
• Then cytoplasmic water from microbial cell
continuously diffuses out and is added in surrounding
ice-crystal.
• The remaining cytoplasm in microbial cell gradually
becomes more and more concentrated.
• High salt concentration in remaining cytoplasm kill the
microbial cell by causing mechanical damage to the
cell.

Cont;
• There are two methods of freezing the food i.e. quick
freezing and slow freezing.
• Slow freezing is more effective in killing microbial
cell but quick freezing is considered more appropriate
for preservation of food.
• When food is frozen very slowly, there is sufficient
time for cytoplasmic water to diffuse out.
• In this case microbial cell is dehydrated to greater
extent. Similarly, larger ice-crystal are formed due to
continuous addition of diffused water into ice.
• Larger ice crystal gives more mechanical damage to
microbial cell.

• However, if larger ice-crystal are formed in food, it gives
more mechanical damage (causes cracking of food) to the
food.
• Therefore, quick freezing is commonly used for food
preservation.
• Although, frozen storage completely prevents microbial
decomposition, it brings several undesirable changes in some
food.
• Some such examples include:
– Protein of food e.g. meat may become dehydrated so that
the food becomes very tough and rigid.
– Myoglobin present in meat may be oxidized into brown
colored meat- myoglobin.
– Fat present in food may be hydrolyzed or oxidized.
– Ice-crystals formed on surface of food evaporate and give
mechanical damage on the surface of food. This damage is
called freeze-burn.

Methods of freezing:
Quick freezing:
– In quick freezing, temperature of the food lowered
very quickly.
– Food is frozen quickly by immersing food into
solution of refrigerant. For.eg. fish frozen by
immersing it into frozen solution of NaCl.
– By blowing frigid air (at -17.8 to -34.4oC) over the
food to be frozen.

Cont;
Slow freezing:
– In this process, temperature of the food is lowered
very slowly.
– Food is frozen slowly by placing it inside the
mechanical refrigerator.
– This technique is commonly used to freeze food in
home.
– However, slow freezing forms larger ice-crystal in
food and give more mechanical damage.
– Therefore, quick freezing is preferred over slow
freezing.

SLOW FREEZING
• It is more effective in killing
micro-organisms in food.
• Larger ice-crystals are
formed.
• Microbial cell is dehydrated
to greater extent.
• It gives more mechanical
damage due to formation of
larger ice-crystal.
• Micro-organisms may adopt
slowly to lower temperature.
• Cold shock does not occur.
QUICK FREEZING
• It is less effective in killing
micro-organisms in food.
• Smaller ice-crystals are
formed.
• Microbial cell is dehydrated
to lesser extent.
• It gives less mechanical
damage due to formation of
larger ice-crystal.
• There is no time for
adaptation.
• Microorganisms may be
killed by cold shock.

Preservation of food by Drying:
• Many spoilage micro-organisms are highly susceptible
to drying.
• Some spoilage organisms are killed rapidly by drying
and growth of most other organism is lowered or,
inhibited by drying.
• Therefore, microbial decomposition of food can be
prevented or at least minimized by drying the food.
• There are different processes of drying food.
• Drying is performed by either evaporation of water
from the food or by lowering Aw value of food by
addition of salt and sugar.
- Cont;

• During drying of food by evaporation, several parameters
like time of drying, humidity of air, temperature of the air
etc. should be controlled.
• Improper control of this parameter brings several
undesirable changes on food.
• For.eg. if food is dried quickly by placing it in very hot
environment, moisture is evaporated only from the surface
but not from inner layer of food.
• In this case, very hard layer is formed on surface that
prevents further dehydration of food.
• This defect is called case hardening.

Different methods of drying food include:
Solar drying:
• In this method, food is dried by placing it in hot
atmosphere of sun.
• Many foods like grains and chopped pieces of
vegetables used for making pickles are dried by this
method.
Drying by mechanical drier:
• In this method, food is dried with the help of some
mechanical drier.
• Liquid food like milk are dried by spray drying and
drum drying method.
• Some liquid foods are dried by placing them in
vacuum chamber of lower temperature.

Cont;
Drying by addition of salt and sugar:
• It is indirect method of drying.
• When salt or sugar is added in food, it binds water in
the form of shell of hydration and make it unavailable
for micro-organisms.
• Therefore, they decrease the amount of available water
(Aw) of food.
• Example of food dried by this method includes
preservation of food by adding high salt concentration
and preservation of milk by adding sugar.

Preservation of food by Radiation (irradiation):
• Two types of radiation are used in food preservation.
They include:
Non-ionizing radiation:
UV light is an example of non-ionizing radiation.
Application of UV light in food preservation:
• UV light is used to kill micro-organisms present in
clear liquid foods. For.eg. it is used to kill yeast cells
and other micro-organisms in fruit juice.
• It is used to inhibit growth of yeast and mold on
surface of some foods like pickles, vinegar, cheese etc.
UV light is commonly used to prevent surface spoilage
of various foods including pickles, vinegar etc.
• UV light is used to disinfect water used for production
of beverages.

Cont;
• It is used to kill micro-organisms present in air of food
processing room.
• It is also used to kill micro-organisms on various food
processing instruments like knife, eating utensils, etc.
• UV light is used in rapid ageing of meat in meat
industries. Ageing is the process of drying meat by
hanging pieces of meat in controlled environment.
Usually meat is aged by hanging it in room at a
temperature of 2.2-3.3oC. At this temperature, ageing
occurs in several months.

Cont;
• Temperature is maintained lower to prevent growth of
micro-organisms in meat during ageing. If ageing is
done at higher temperature micro-organisms grow in
meat and spoil it before ageing takes place.
• In rapid ageing technique temperature of room is
maintained around 18oC and UV light is used to
inhibit growth of micro-organisms in meat during
ageing. At this temperature ageing occurs in 2-3 days.

Ionizing radiation: (Cold sterilization)
• X-ray, γ-ray and cathode ray are examples of ionizing
radiation.
• They are powerful oxidizing agents and kill the
microbial cell by oxidizing various cellular materials.
• Some common ionizing radiation used in food
industry include:
X-ray:
– Production of X ray is expensive.
– Furthermore, its penetration power is lower.
Therefore, it is not commonly used in food
preservation.

Cont;
• γ-ray:
– It has good penetration power and it can penetrate
up to 20cm even in solid food.
– γ-ray is emitted in all direction from the source.
Therefore it is difficult to make γ-ray to hit the
food.
– So, efficiency of γ-ray in food preservation is only
10-25%.

Cont;
Cathode ray:
– Cathode ray is directional and it is emitted in only
one direction.
– Therefore, efficiency of cathode ray in food
preservation is high (up to 40-80%).
– Unfortunately, it has lower penetration power and
can penetrate only up to 0.5cm in solid.

Applications of ionizing radiation in food processing:
• Some applications of ionizing radiation in food preservation
includes:
• Low level of ionizing radiation is used to kill
microorganisms on fresh fruits and vegetables. It is used to
kill insect as well as microorganisms on vegetable and fruits.
• High level of ionizing radiation is used to kill
microorganisms and insect on dry vegetable and fruits.
• Ionizing radiation are commonly used to preserve meat and
meat product. For.eg. irradiation is commonly used to inhibit
microorganisms, nematodes and other parasites present in
meat and meat products.

Cont;
Undesirable changes of ionizing radiation:
• In meat, it increases pH, damage glutathione, increase
carbonyl compound and generate bad smelling
compound like H2S and methylmercaptan.
• In fatty food, it damages natural anti-oxidant and
increases chance of oxidative rancidity.
• It causes loss of several vitamins like pyridoxine,
thiamine, vit. C, vit. D, vit. A, vit. B12. Therefore, it
reduces nutritional value of food.

Chemical agents used in preservation of food:
• Different types of chemical preservative are used to
preserve variety of food.
• Chemical preservatives are utilized in food preservation
in various ways as given below:
– Some food preservatives are directly mixed with the
food to be preserved.
– Some chemical preservative are used in wrapper or
container of food rather than in food itself.
– Some chemical preservative are placed in air of
storage environment of food.
– Some chemical preservative are used for treatment of
equipment used in food processing.

Cont;
• Not all food preservative can be used to preserve ah types
of food.
• It is because some chemical preservative brings some
undesirable changes for.eg. change in taste, smell etc. in
some food. For.eg. spices are usually not considered
suitable for preservation of milk and milk product because
taste of spices in milk product is not considered desirable.
• Some chemical food preservatives used in preservation of
food include:

a) Organic acids: Examples
I) PROPIONIC ACID AND PROPIONATE:
– Propionic acid is naturally found in Swiss cheese as a
developed preservative up to a level of 1% .
– Na and Ca propionate are commonly used to inhibit
growth of mold in bakery product like bread.
– Propionic acid and propionate are effect against mold,
with very little or no effect against bacteria and yeast.
– Therefore they are added in food which usually
undergo mold spoilage

ii) Benzoic acid and benzoate
– Sodium benzoate us used to preserve variety of food
like jam, jellies, carbonated beverages, fruits etc.
– It is most effective at power pH and it’s anti-
microbial activity decreases with increase in pH.
– Therefore, it is usually used to preserve acidic and
slightly acidic food. At pH of 2.5-4 it is effective
against most bacteria, some yeast and mold.
– Methyl paraben and propyl paraben which are
derivative of benzoic acid are also commonly used to
preserve variety of food.
– Their advantages over benzoate is that they are more
effective at higher pH.

iii) Sorbic acid and sorbates:
– Sorbic acid and its Ca, Na and K salt are used as
antimicrobial agent to preserve various food.
– They are effective against yeast and mold but less
effective against bacteria.
– Their antimicrobial activity is high at lower pH.
– Therefore they are used in slightly acidic food like
pickles, fruit juice, syrup and other foods like cheese,
bakery product etc. to inhibit growth of mold and yeast.

iv) Acetic acid and acetates:
– Acetic acid and its derivatives like monochloroacetic
acid, peracetic acid, dehydroacetic acid and sodium
diacetate are used as food preservatives.
– Some examples include;
– Dehydroacetic acid is used to treat wrappers of cheese
to inhibit growth of mold on the surface of cheese.
– Acetic acid in the form of vinegar is added in the form
of vinegar is added in pickles to inhibit growth of
microorganisms. Its activity increases with decrease in
pH.
– Sodium diacetate is used in malt syrup. It is also used
to treat wrapper of butter.

v) Nitrites and nitrates:
– Nitrite and nitrate of Na and K are used in curing
solution or curing mixture of meat.
– They have slightly bacteriostatic action, but they are
added in meat mainly to fix red colour.
– In acid environment, nitrite decomposed into nitric
acid which reacts with haeme pigment of meat to
form nitrosomyoglobin that gives attractive red
colour to the meat.
– Nitrite is a real colour fixative and nitrate is used as
a source of nitrite.
– Nitrite can react with secondary and tertiary amine
to form nitrosamine which is carcinogenic.
– Nitrite and nitrate are mainly used to fix red colour
to meat but not to preserve it.

b) Smoking (wood smoke):
– Smoking is a method of preservation of meat by
exposing it to wood smoke.
– Two main purpose of smoking of meat are to add
desirable flavor and to preserve the meat.
– Some other desirable changes include improvement
in colour, drying, and tenderization of meat.
– Wood smoke contains large no of volatile
compounds having bacteriostatic and bactericidal
activity that help in preservation of meat.
– Some such compound include formaldehyde, phenol,
cresol, aliphatic acid, acetaldehyde, ketones and
others.
– Wood smoke also contains variety of flavoring
compound that give desirable flavor to the meat.

c) SO2 and sulphites:
– SO2 and sulphites are used in wine industry to sanitize
equipment's and to reduce number of normal flora of
grape must.
– In aqueous solution, SO2 and sulphites form sulfurous
acid which is anti-microbial.
– Fume of burning sulfur are used to treat fruits and
vegetables.
– SO2 is also added in fruit juice, syrup and various
wine.

d) Sugar and salt:
– Sugar and salt are added in variety of food.
– For.eg. milk is preserved for long time by adding high
concentration of sugar.
– Similarly, foods like pickles, fish etc. are preserved by
adding high concentrations of NaCl.
– Preservative action of salt and sugar include:
– They bind water and make it unavailable for growth of
microorganisms i.e. reduce Aw value of food.
– Sugar increases osmotic pressure and causes osmotic
lysis of microbial cell.
– They draw out moisture from food and help in drying of
the food.

e) Formaldehyde:
– It is highly poisonous and is not permitted in food
except as a minor component of wood smoke.
– In food industry, it is used to sterilize equipment
and to kill microorganisms in air of food
processing room.
– It is highly antimicrobial and can kill fungi,
bacteria, spore and viruses.

f) Alcohol:
– Ethanol is anti-microbial.
– Excellent keeping quality of some food is due to
their alcohol content.
– Ethanol content of soft drinks like beer is not
sufficient to completely kill microorganisms but it
slows down growth and activity of spoilage
organism.
– Alcoholic content of distilled alcoholic beverages is
sufficient to prevent microbial spoilage.
– Some food products like lemon extract (eg. Jolley)
are also preserved by addition of ethanol.

g) Ethylene and propylene oxide:
– Ethylene and propylene oxide are gaseous
sterilizing agents.
– They are used to sterilize packaged food like dried
food.
– Furthermore, ethylene oxide is also used to kill
microorganisms in air of food processing room.

h) Spices and other condiments:
– Spices and other condiments added in food for taste and
flavor are anti-microbial and help in food preservation.
– Antimicrobial activity differs with type of spices.
For.eg. mustard, flour and mustard oil are effective
against like Saccharomyces but are less effective against
bacteria.
– Cinnamon and cloves is added in food are very effective
against bacteria.
– Similarly, garlic and onion mixed in food are
bacteriostatic or bactericidal.
– However, not all spices can be added in all types of food
products because their taste and flavor maybe
considered undesirable in certain food.

Cont;
i) Antibiotics:
– Use of antibiotics in food preservation is not
permitted due to risk of development of antibiotic
resistant microorganisms.

Food Preservation .

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