U3 Canning of foods and preservation methods

Food process

1. Thermal processing CANNING

2. Definition:
Canning means, the preservation of food
in permanent, hermetically sealed containers
(of metal, glass, thermostable plastic, or a
multi- layered flexible pouch) through
agency of heat. Heating is the principle
factor to destroy the microorganisms and the
permanent sealing is to prevent re-infection.
CANNING

4. Containers for canned foods:

5. Can materials:
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.
(a) Steel:
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 .

6. 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) acid- resistant 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.

7. (b) Aluminum
(c) Plastic
(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 effectsof lighton 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.

8. 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 classification.

9. 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 non-
sporing bacteria and all spores that might germinate and grow
during storage without refrigeration.

10. (I)Canning operation:
(A) Preparatory process
(1)Receiving and storage of raw materials: (2)
Preparation procedures
(i)Thawing(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

11. (B) Production processes
(i)Blanching: (parboiling)
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 :
Inactivatesenzymes reaction,whichmay
occurduring preparation periods.
Aids in cleaning. Expels internal gases.
Aids in filling of containers by shrinkage or softening of
the food.
Assure adequate can vacuum.
Destroys many vegetative microbial cells. Steam blanching is
preferable than hot water.

12. (ii) Grinding:
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
blend.

13. (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, spices.

14. (iv) Filling of cans
The mix is then transferred to automatic piston-type-
filters 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.

16. (v) Exhausting and sealing:
Exhaustion or removal of air from the can before it is sealed,
is necessary for the following reasons:
1-) Toprevent expansion of thecontents
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)

18. (vi) Washing
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).

19. (vii) Thermal processing:
Thecansmustbeprocessed(heattreated)
afterclosing(hermeticsealed)atimmediately
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 heating .
vegetative bacteria are killed at 80C/30min. Spore
formers at a temp.110C/30min.
For destroying the spores 121C/3min.

21. 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

22. (viii) Cooling
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.

24. (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

26. 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% relative humidity.
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.

28. Spoilage ofCanned
Foods

29. (A)Spoilageofcannedmeat
according condition and content of the
can:
tothe
1-Swell:bulgingofbothcanendsby
+ve
internal
pressureduetogasgeneratedbymicrobial
or chemical activity. Either hard or soft
swell.
•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.
•springer: a can bulged from one end which if forced
back into normal position, the opposite end bulgs.
•Leakage: perforated can.
•overfilled can: has convex ends due to
overfilling and not regarded as spoiled.

30. (B) Spoilage of canned meat according to
the cause:
(i) - Microbial spoilage:
May result from insufficient processing or leakage.
-3 types of spore forming bacteria:
1gas producing anaerobes and aerobes with optimum
growth temp. 37 C.
2gas producing anaerobes with opt. temp. 55 C.
3Non-gas producing aerobes or facultative anaerobes
with opt. temp. 55 C.-------produce flat souring.
-Leak can be detected by:
1Bubbles when squeezed under water.
2Disappearance ofvacuum (concavity)
when heated to 38 C followed by slow cooling.

31. Flat souring :
high acid formation without gas production.
-Caused by thermophilic bacteria:
1Bacillus coagulans.
2Bacillus stearothermophilus.
3Bacillus circulans.
-----------thesebacteria
attck
CHO
producingacid without gas.
-Common in tropical and subtropical countries
-Affected cans should be condemned.

32. (ii)- Chemical spoilage:
1- Hydrogen swell:
-
-
-Notrelatedtofermentationor
bacterialspoilage.
-Can show varying degree of bulging------when
opened-----odorless burnable gas.
Quite harmless but undifferentiated from swell
of spoiled can So, it is rejected.
-

33. 2- Sulphiding (Sulphur stinker spoilage):
-
-
-