The most important task of food industry and also food scientists is to ensure
the food safety which provided to the consumers so the food quality and food
safety has become a major aim for the consumer
We must know the topical aspect of food quality and food safety
Most food are derived from animal origin and plant origin and from some
microorganisms by biotechnology method so most parts of food is edible
biochemical then the good application of the food processing and storage and
preservation will prevent the out breaks of food borne diseases which is
resulted from using of contaminated food.
Method of food preservation are: 1) Physical removal of microorganisms
(centrifugation, filtration and trimming). 2) Heat treatment 3) Radiation 4)
High pressure 5) UV Radiation 6) Bacteriocins 7) Combined method and
other methods used for preservation of food.
Food preservation is a method which done to increase the shelf life of foods,
keep food at high level quality as long as possible and to facilitate storage and
Method of food preservation:
Physical removal of microorganisms: It is used to reduce the microbial
level and composed of centrifugation, filtration and trimming.
Centrifugation it is used in liquid foods as milk to remove suspended
undesirable particles under high pressure.
Filtration is used in heat sensitive nutrients like concentrated juice.
Trimming and washing used to remove areas that are heavily contaminated
with microorganism in processed food.
Also effective against mold as mold can be removed physically from the
surface of some kind of cheese during the curing process
Preservation by heat treatment
Heat is the most commonly used method of food preservation. The degrees
of preservation of food by heat are various and depend on the type final
product manufactured which may be pasteurization and sterilization.
Some microorganisms are heat resistant such clostridium botulinum which is
spore forming anaerobic bacteria that produce one of the most harmful toxins.
The thermal death time is the time of heating for killing all vegetative cells of
microorganisms. The rate of killing of microorganisms by heat is proportional
to the number of cells of the organism.
Low heat preservation the temperature in this method is below 100c like
pasteurization which destroy all the vegetative cells of the microorganisms
also affect 90% of spoilage microorganisms as yeasts and molds and some
enzymes like lipase and phosphatase in milk to minimize the thermal damage
of food and prevent reduction of acceptance quality the temperature and time
are set to the lowest level.
It is used for preservation and processing of many products e.g. Pasteurization
of cream for making butter and also used in cheese and yoghurt.
High heat temperature the temperature degree used in this process is at or
above 100c for desired period of time
Sterility is high heat temperature process that can be achieved by heating a
food at very high temperature for short time e.g. UHT milk processing to
increase the shelf life of milk up to 3-6 months.
Boiling this method is used for preservation of milk but it cause changing in
the appearance and palatability and digestibility and nutritive properties of
milk. Steam under pressure this method is used mainly in evaporate and
condensed milk to increase the shelf life of the products.
Preservation by radiation
It is a cold sterilization process so the irradiated food not shows the damaging
effect of heat on the food quality. But the disadvantages of this process is it
may cause oxidation of lipids and denature of food proteins especially in high
doses may cause burnt flavor or rancid odor this method if effective against
molds and yeasts and virus and bacterial cells and spores. But it doesn’t
destroy toxins or undesirable enzymes in food. The rays used in food
preservation are Ultra violet X and B and Gamma rays.
This method is divided into direct and in direct. It is used in pasteurization
and extending the storage of milk product and poultry and beef by killing of
spoilage microorganisms also used in improving the quality of products.
Preservation by high pressure
A new method of food preservation. It is non-thermal food processing
method. High hydrostatic pressure is applied on the food which leads to
inactivation of vegetative microorganism at pressure 400-600 mpa at while
some spores may resist more than 1000 mpa at room temperature.
This method affects mainly gram negative bacteria. This method also
Preservation by ultra violet radiation
Depend on the bactericidal effect of light. Mainly used in thin liquid films as
it has low penetration waves and when it used in high dose causes odor and
flavor deterioration. When low dose applied it can lead to extend the shelf life
Also use in sterilizing of air and killing the bacteria in water as it does not
affect the taste of water. Bactericidal UV lamps also used in wrapping of
cheese and to prevent mold growth on the surface of bakery products.
Preservation by combined method
It based on combination of some preservative factors which the
microorganisms are unable overcome. It is used to prevent microbial spoilage
and prevent food poisoning.
It is used in developed countries to make foods storable without refrigeration
The advantage of this method is that the food which is preserved by this
method is stable and safe and nutritious and stable and economical and tasty.
Preservation by application of bacteriocins
Bacteriocins are a protein produced by some microorganisms that has
bactericidal effect against some microorganisms. It has high resistance to high
temperature. About 30 different types of bacteriocines is known
E.g. some staphylococcus strains produce epidermin and e.coli produce
colicin but it is unsuitable for applying in food. It is also used to inhibit gram
The first bacteriocin that was used in food preservation is niacin.
Also is used as starter in some dairy products. Another type of bacteriocin is
pediocin which is produced by bacteria called pediococcus.
There many types of pediocin which are used to inhibit the growth of several
clostridia and bacillus cereus and staphylococcus aureus and broad range of
lactic acid bacteria and listeria monocytogenes.
Also used for inhibiting the growth of meat spoilage bacteria so it increase the
raw meat shelf life . The most common used source of bacteriocins is lactic
acid producing bacteria.
This method used to increase the period of shelf life of milk also used in swiss
type cheese to prevent the blowing faults which caused by clostridia and used
in some canned foods to prevent its spoilage by thermophiles bacteria
Preservation by low temperature
Preservation of food by cooling and freezing is used to reduce
microbiological and biochemical changes rate so it extend the shelf life of
fresh and also processed food the storage temperature is from -1 to +1 is used for storage of fresh fish and meat from 0 to +5for storage of cream prepared
salads pasteurized milk and yoghurt from 0 to 8 storage of butter, margarine
Refrigeration this temperature are used for production of milk of good quality
including storage of milk on farms and transportation and after pasteurization
and storage of milk products until consumption. The refrigeration temperature
Some refrigerated foods may have storage life of 60 day or more.Freezing a
method of preservation of food by storage of food products at temperature
blew freezing point in which the state of Water changes to form ice crystals
So the food is preserved under to methods low temperature and reducing
The temperature used in home freezer is -20c. The temperature used for storage of butter ice cream and cream is -17 to -29c.
Potential food preservation
Preservation of food by addition of few additives or few external treatments.
The advantage of this method is the high quality of food products. The food
will be more As consumers in this days prefer foods with high quality and
high nutritive value and fresh like attribute this mean fewer additives and
fewer external treatment are used freshness and less heat damage and less acid
and sugar and salt.
Preservation by controlled atmosphere
It can be used by controlling the humidity and gas composition and
temperature. This provides a long term storage of food. It is mainly used for
transportation and bulk storage.
It is difficult to maintain a constant gas phase but modification of
atmosphere is possible.
This method is used in large storage of fresh and processed food like
fish and meat and vegetables and fruits.
Modifying atmosphere to make it suitable for food preservation can be
achieved through three levels.
Controlled atmosphere used for bulk storage and also transportation by
controlling humidity and gas composition and temperature to provide
optimal condition for food products which lead to increase the shelf life
of foods as meat and fruits
Gas packaging it is used in retail packs and bulk storage by using gas
mixture. Vacuum packaging it is used in retail packs by evacuation if
the original air atmosphere.
Preservation by addition of substances
The most common substances used are carbon dioxide, nitrate, nitrite and
Sulphite is used to inhibit enzymes catalyzed reaction.
Nitrate and nitrite inhibit the growth of spoilage and pathogenic
microorganisms such as cl.botulinum.
The antimicrobial effectiveness of nitrate is increased when the ph is lowered
The nitrite is used to inhibit the growth of cl.botulinum and also is used in
cured meat to prevent rancidity.
Carbon dioxide it is effective against psychotropic microorganisms when its
concentration is more than 5%.
It is used in modified atmosphere to extend the shelf life of refrigerated food
as it inhibits the growth of psychotropic bacteria
Preservation by addition of organic acid
Using of week organic acid to reduce the ph of food to control microbial
growth. According to acidity food can be classified into nonacid (7_5.3) and
low acid (5.3_4.8) and acid (3.7) or lower.
The optimum ph required for most bacterial growth is near 6.8 but some
bacteria can multiply when ph is 4. Moulds and yeasts can grow at ph less
than 2. The growth rate of microorganisms reduces when the ph is reduced
below optimum range.
Some organic acid produced by food fermentation also reduce the
Sorbic or propionic acid is permitted in cheese and yoghurt and also hard and
soft cheese to prevent the growth of molds on the surface and to extend it is
Reducing the ph will also make bacterial spores susceptible to heat treatment
Low concentration of organic acid is mainly used to prevent growth of yeast
and moulds. Acetic acid is an organic acid which is used as food preservative
at concentration (0.04%)
Propionic acid the calcium and sodium salts are mainly used against moulds
Lactic acid (at ph 5) is used as inhibitor for spore forming bacteria but it
doesn’t affect yeasts or moulds
Sorbic acid is effective against moulds and yeasts more than bacteria
Benzoic acid is used against bacteria and moulds and yeasts.
Preservation of food by low water activity
Reducing of water activity can be achieved by partial removal of water or by
increasing the osmotic pressure by addition of some substances as ethanol or
salts or sugar.
This method is mainly used to reduce the growth of vegetative cells and out
growth is spores of microorganisms and also prevent Production of toxin by
toxigenic bacteria and moulds.
Preservation of food by pulsed electric shock
The use of electric arch to generate a shock wave which cause inactivation of
microorganisms by forming spores in cell membrane.