Canning means, the preservation of food in
permanent, hermetically sealed containers (of
metal, glass, thermostable plastic, or a multilayered flexible pouch) through agency of
heat. Heating is the principle factor to destroy
the microorganisms and the permanent sealing
is to prevent re-infection.
Containers for canned foods:
The container plays a vital role in food
canning, it must be:
1-) Capable of being hermetically sealed to prevent
entry of microorganisms.
2-) Impermeable to liquids and gases, including
3-) Maintain the state of biological stability (i.e,
commercial sterility) that was induced by the
thermal process alone or in combination with
other chemical and physical processes.
4-) Physically protect the contents against damage
Wide varieties of materials are used now for
manufacture of cans for meat and poultry
preservation. Yet metal containers remain the most
frequent used package for canning foods.
Tinplate, tin-free steel, and nickel-plated steel coated
with a very thin film of tin are the materials used to
manufacture metal food cans.
The amount of tin used being only about 1.5% of the
can’s weight and should not contain more than 1%
lead. It is used to prevent rusting .
To prevent interaction between meat product and
the metal, cans are coated on the inside with an
organic material. Two general kinds of organic
coatings are used in the food industry : (i) acidresistant and (ii) sulfur-resistant. Acid-resistant
coated cans are used primarily for fruit. Meat
products are generally packed in cans that have been
lined with sulfur-resistant materials.
(d) Glass containers and metal closures
Although the wide variety of containers for canned foods, the
metal ones are preferable as:
1-) It has a high conductivity of heat.
2-) It cannot easily be broken.
3-) Being opaque, so any possible bad effects of light on
food stuffs are avoided.
4-) Be able to withstand the stresses imposed during thermal
processing and cooling.
5-) Be able to withstand the subsequent handling, which
includes transportation, storage and distribution.
Important food groups
(a) Low acid foods: Meat, fish, poultry, dairy fall
into a pH range of 5.0 to 6.8. This large group is
commonly referred to as the low acid group.
(b) Acid foods: With pH values between 4.5 and
3.7. Fruits such as pear, oranges, apricots and
tomatoes fall in this class.
(c) High acid foods: Such as pickled products
and fermented foods. The pH values range from 3.7
down to 2.3, also Jams and Jellies are in this
Preservation of meat by high temperature “canning”
commercial sterilized canned meat”
In which all or most bacteria are killed,
In practice, complete sterility is seldom achieved, in the
fact that certain microorganisms form spores, which may be
heat-resistant. To destroy the spores of certain thermophiles
would require a degree of heating which would greatly lower
the organoleptic characteristics of canned meat products.
In canning practice “commercial sterility” is achieved by
giving a degree of heat treatment sufficient to kill nonsporing bacteria and all spores that might germinate and grow
during storage without refrigeration.
(A) Preparatory process
(1)Receiving and storage of raw materials:
(2) Preparation procedures
(ii) Boning, cutting and trimming
On the trimming table where the inedible parts
(such as bones, cartilages blood clots, skins and
tendons together with the increased fat are removed.
In fish,head,fins,scals and viscera also are removed
(B) Production processes
This is a heat treatment given to many foods prior to canning
in hot water (100°C) for 1½-5 minutes, it may extend to 9-11
minutes in some types of fruit and vegetable. Blanching is
significance to :
Inactivates enzymes reaction, which may occur during
Aids in cleaning.
Expels internal gases.
Aids in filling of containers by shrinkage or softening of
Assure adequate can vacuum.
Destroys many vegetative microbial cells.
Steam blanching is preferable than hot water.
Meat cuts of variable size and shape and with a
variable fat content are ground to form uniform
particles of fat and lean. Proper mixing of these
particles is extremely important to obtain a uniform
(iii) Mixing with addition of suitable ingredients:
Particles of fat and lean obtained by grinding are
tumbled in a mixer to give a uniform distribution of
fat and lean particles, and with suitable additions of
required ingredients as salt, sodium nitrite, sugar,
(iv) Filling of cans
The mix is then transferred to automatic piston-typefilters and packed into the appropriate cans on the fill
line with required weights
The head space volume or depth should be
checked due to its critical factor in the attainment of
an appropriate vacuum closure.
Such process should be carefully controlled due to:
a-) economic aspect
b-) Efficiency of exhausting procedure.
c) Rate of heat penetration.
(v) Exhausting and sealing:
Exhaustion or removal of air from the can before it is sealed,
is necessary for the following reasons:
1-) To prevent expansion of the contents during processing
which may force the seam.
2-) To produce concave can ends so that any internal pressure
may be readily detected and the can rejected.
3-) To lower the amount of oxygen in the can and prevent
discolouration of the food surface.
4-)To reduce chemical action between the food and container
and hydrogen swells.
5-)To prevent internal corrosion of the cans.
Exhausting methods a) Thermal exhausting (Steam vacuum)
(b) Mechanical exhausting: (machine vacuum)
After the cans are closed, they pass through a
detergent spray washer to remove grease and
other material. The washing should consist of
hot water (66°C) then by suitable pre-rinse,
detergent spray wash. Followed by a fresh
warm water rinse (66°C).
(vii) Thermal processing:
The cans must be processed (heat treated)
immediately after closing (hermetic sealed) at
suitable time and temperature
Food to be canned is threatened on the one hand by
bacterial spoilage (if under processed) and on the
other by danger of lower the nutritive quality by over
vegetative bacteria are killed at 80C/30min.
Spore formers at a temp.110C/30min.
For destroying the spores 121C/3min.
The total time required to sterilize canned food is
largely depends on:
a) Size of can.
b) Processing temperature
c) Rate of heat penetration at the center of the can.
d) pH of the food
e) The type and number of organisms present.
During processing, heat penetrates to the centre of
the can by “conduction” and by “convection”
currents. In solid meat packs, the heat diffuses by
conduction and the process is therefore, slow, the
convection current in loosely packed foodstuffs
transfer heat faster
Immediately after processing, the cans are cooled in
water to a temperature of 36°C to 42°C. to avoid
thermophilic spoilage or can rust. If the cans are cooled
much below 36°C, they may not dry thoroughly and
rusting well result. If the cans are cased at temperatures
much over 42°C, thermophilic spoilage may occur.
only potable water, as defined in International
Standards of Drinking Water (WHO) should be used in
food handling or as an ingredient.
(ix) Container washing
Cans that have just been cooled are dirty and greasy
on the outside, and are therefore washed in a bath with
detergent and then rinsed to facilitate subsequent handling.
(x) Container drying:
Cooled cans should be immediately dried as the externally
dry seams and closures are almost free from microbial
One method that has been found to be quite efficient is the
heated bed drier, which rolls cans over a surface heated by
steam to 127-130°C covered by an absorbent cloth.
Contaminating bacteria are rapidly killed at these
(xi) Outside lacquering
Commercial lacquer or enamel is a coloured varnish
containing vegetable or synthetic resin Lacquer may be
applied to the outside of the can to prevent external corrosion.
(xii) Testing of post-processed container
Processed cans should be incubated at, for example, 30°C for
14 days and/or 37°C for 10-14 days. In addition, if the
product is intended to be distributed in areas of the world
with tropical climate or is to be maintained at elevated
temperatures containers should also be incubated at higher
temperatures (5 days at 55°C). Since thermophiles may die
during such incubation period, it is advisable to examine
containers periodically for the evidence of gas production
before the end of incubation
(xiii) Labeling and casing
The role of a label is to inform. The information can be
grouped as follow:
Product identification (corned beef, beef stew, luncheon)
and grade (fancy, choice, standard).
Brand name, a distinctive name protected by trademark
Net contents by weight or volume.
List of ingredients including additives as per the
Country of origin if the product was not processed in the
country in which it will be offered for sale.
Production date and the shelf life should be clarified.
b) Casing: (Protective covering)
Containers are usually cased immediately after labeling.
Casing which was formerly a manual operation is now
highly automated in most canneries.
(xiv) Storage and shelf life
Commercially sterile canned meats should be placed
in a cool, dry place since both relative humidity and
temperature influence their keeping quality. The storage
place must be dry, preferably no more than 30-40%
Storage temperatures of sterile canned meat products
should not be above 21.1°C, because higher
temperatures markedly accelerate deterioration during
storage, thus limiting shelf life.
(A) Spoilage of canned meat according to the
condition and content of the can:
1- Swell: bulging of both can ends by +ve internal
pressure due to gas generated by microbial or
chemical activity. Either hard or soft swell.
2- flipper: a can with normal appearance but one end
flips out when the can is struck against a solid object
but snaps back to the normal under light pressure.
3- springer: a can bulged from one end which if forced
back into normal position, the opposite end bulgs.
4- Leakage: perforated can.
5- overfilled can: has convex ends due to overfilling
and not regarded as spoiled.
(B) Spoilage of canned meat according to
(i) - Microbial spoilage:
May result from insufficient processing or leakage.
- 3 types of spore forming bacteria:
1- gas producing anaerobes and aerobes with optimum
growth temp. 37 C.
2- gas producing anaerobes with opt. temp. 55 C.
3- Non-gas producing aerobes or facultative anaerobes
with opt. temp. 55 C.-------produce flat souring.
- Leak can be detected by:
1- Bubbles when squeezed under water.
2- Disappearance of vacuum (concavity) when heated
to 38 C followed by slow cooling.
Flat souring :
high acid formation without gas production.
- Sour odour, bitter taste, container not swollen.
- Caused by thermophilic bacteria:
1- Bacillus coagulans.
2- Bacillus stearothermophilus.
3- Bacillus circulans.
-----------these bacteria attck CHO producing
acid without gas.
- Common in tropical and subtropical countries
- Affected cans should be condemned.
(ii)- Chemical spoilage:
1- Hydrogen swell:
Formation of hydrogen gas in can due to
internal corrosion or scratch.
- Occur mainly in acidic foods (canned fruits).
- Rarely in canned meat but seen in canned
- Not related to fermentation or bacterial
- Can show varying degree of bulging------when
opened-----odorless burnable gas.
- Quite harmless but undifferentiated from swell
of spoiled can So, it is rejected.
2- Sulphiding (Sulphur stinker spoilage):
Discolouration of inside of can with pink to
- Occur due to reaction of sulphur-containing
proteins (liver, kidney, tongue) with liberated
H2S from bacterial spoilage (Cl. nigrificans
(sulphur stinker)) with the odor of rotted egg.
- It may be accompanied with blackening when
H2S react with steel base of tin forming iron
sulphide and may lead to pitting.
- Sulphiding can be prevented by-------sulphurresistant lacquer.
(iii)- Rust and damage:
Rust------ reddish brown ferric oxide seen
- Slight rust----pass for rapid consumption.
- Severe rust---condemned and rejected.
- Slight damage-----pass for rapid
- severe damage------rejected.
Preservation of meat by radiation
(Irradiation of meat):
.Long wave length- 1
.Short wave length- 1
Low penetrating power (surface- 2 .High penetrating power- 2
Associated with rise in product-3
Not associated with rise in- 3
.e.g. – Infra red rays- 4
e.g. – X rays- 4
1- Preservation of very large meat cuts.
2- Killing all vegetative cells including
salmonella, campylobacter, listeria.
3- No change in physical and chemical
composition of meat.
1- Vitamins destruction.
2- Off-flavours( fat oxidation by generating
3- probable carcinogenic effect and public
distrust of irradiation.
Preservation of meat by antibiotics
The choice of suitable antibiotics depend on:
- The type of spoilage to be controlled.
- The stability and solubility of antibiotic at the
pH of the food.
- Its stability to heat (Nisin, Tylosin).
- Its lack of toxicity.
Methods of antibiotic application:
1- Feeding the antibiotic for a short period
2- Injection of antibiotic pre slaughter.
3- Perfusing the whole or quartered carcase by
4- spraying of antibiotics on the carcase or cut
5- the meat may be dipped in an antibiotic
6- Using the antibiotics as an aid to processing
ttt such as sterilization during canning thus
lower heat ttt for processed foods.
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