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CANNED FOODS
CANNING
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Canning is a method of preserving food in which
the food contents are processed and sealed in an
airtight container.
Canning provides a typical shelf life ranging
from one to five years, although under specific
circumstances a freeze-dried canned product,
such as canned, dried lentils, can last as long as
30 years in an edible state
To prevent the food from being spoiled a number
of methods are used: pasteurisation, boiling (and
other applications of high temperature over a
period of time), refrigeration, freezing, drying,
vacuum treatment, antimicrobial agents are used
SAFE CANNING METHODS
The boiling water bath method is safe for
tomatoes, fruits, jams, jellies, pickles and other
preserves. In this method, jars of food are heated
completely covered with boiling water (212°F at
sea level) and cooked for a specified amount of
time
 Pressure canning is the only safe method of
preserving vegetables, meats, poultry and
seafood.
 Jars of food are placed in 2 to 3 inches of water
in a special pressure cooker which is heated to a
temperature of at least 240° F.
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This temperature can only be reached using the
pressure method.
 A microorganism called Clostridium botulinum
is the main reason why pressure processing is
necessary.
 Though the bacterial cells are killed at boiling
temperatures, they can form spores that can
withstand these temperatures.
 The spores grow well in low acid foods, in the
absence of air, such as in canned low acidic foods
like meats and vegetables. When the spores begin
to grow, they produce the deadly botulinum
toxins(poisons)
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Foods that are low acid have a pH of more than
4.6 and because of the danger of botulism, they
must be prepared in a pressure canner.
 The low acidic foods include:
 meats
 seafood
 poultry
 dairy products
 all vegetables
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High acid foods have a pH of 4.6 or less and
contain enough acid so that the Clostridium
botulinum spores can not grow and produce their
deadly toxin. High acidic foods can be safely
canned using the boiling water bath method.
 The high acidic foods include:
 fruits
 properly pickled vegetables
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FACTORS THAT LIMIT THE SHELF
LIFE OF CANNED FOODS
Cans or glass jars with metal lid can get rusted if
not used properly
 Cans could even corrode, if food will chemically
react with metal container. Especially highly-acid
food like canned tomatoes and fruit juices gets
easily corroded.
 Temperatures over 100 degrees Fahrenheit are
harmful for canned foods. If the storage
temperature rises, the risk of spoilage of food,
jumps sharply. There are high chances of loosing
nutrient of the caned food, if stored at above 75
degree for very long period
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SPOILAGE OF CANNED FOODS
The most important kind of chemical spoilage of
canned foods is hydrogen swell, resulting from
the pressure of hydrogen gas released by the
action of acid of a food on the iron of the can
 Hydrogen swells favored by:
 Increase in acidities of foods
 Increase in tempratures of storage
 Imperfections in the tinning and lacquering of
the interior of the can
 Presence of soluble sulphurs and phosphorus
compounds
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TYPES OF SPOILAGE OF CANNED
FOODS
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Three most important kinds of biological spoilage
of commercially canned foods are:
flat sour spoilage
TA spoilage
putrefacation
A fourth kind of spoilage caused by the action of
food on the iron of the can,results in hydrogen
swell
FLAT SOUR SPOILAGE
This kind spoilage occurs when canned food
remain flat during souring or by development of
lactic acid in the food by the flat sour bacteria
 This spoilage occurs chiefly in low acid foods such
as peas and corn and is caused by species of
Bacillus
 Flat sour spoilage of acid foods like tomatoes or
tomato juice is caused by special facultatively
thermophillic species bacillus coagulans
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Various species of bacillus that are able to form
acid without gas in food may be
mesophilies,facultative thermophilies or obligate
thermophilies
 The spores of mesophilies are less heat resistant
and killed by heating process and hence are
rarely concerned with flat sour spoilage
 the spores of thermophilies are more heat
resistant and may survive the heat process and
cause flat sour spoilage
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TA SPOILAGE
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This is a thermophillic spore forming anaerobe
that forms acid and gas in foods
The gas(mixture of carbon dioxide and hydrogen)
swell the can if it is held long enough at a high
temprature and may eventually cause bursting
The spoiled food usually has a sour odour.
Sources are same as for flat sources bacteria
SULFIDE OR SULFUR STINKER
SPOILAGE
Spoilage caused by Desulfotomaculum nigrificans
 Found in low acidic foods such as peas and corn
 Spores of this bacterium are less heat resistant
than those of flat sour and TA bacteria
 The organism is an obligate thermophile and
therefore also requires poor cooling of heat
processed foods or hot storage for its
development
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TYPES OF SPOILAGE BY MESOPHILIC
SPORE FORMING BACTERIA
MOST SPOILAGE BY MESOPHLIC MICROORGANISMS
THAT RESULTS FROM UNDERPROCESSING IS
CAUSED BY SPORE FORMING BACTERIA OF THE
GENERA BACILLUS AND CLOSTRIDIUM
SPOILAGE BY MESOPHILIC clostridium
species:
 Sugar fermenting species of clostridium –egc.butyricum and c.pasteurianum causes butyric
acid fermentation in acidic foods by release of
carbon dioxide and hydrogen
 Other species such as
C. sporogenes,C.putrefaciens,C.botulinum are
proteolytic or putrefactive decomposing proteins with
the production of malodorous compounds such as
hydrogen sulfide,ammonia,indole and skatole
Putrefacative anaerobes also produce carbon dioxide
and hydrogen,causing the can to swell
 Canned acid foods such as pineapple,tomatoes
and pears have been found spoiled by
C.pasteurianum
 Putrefactive anerobes grow best in the low acid –
canned foods such as peas,corn,meat,fish and
poultry
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SPOILAGE BY MESOPHILLIC bacillus
SPECIES:
 Spores of various species of Bacillus differ
considerably in their heat resistance
 Spores of many of the mesophillies are killed in a
short time 100 C` or less but few can survive the
heat treatments employed in steam-pressure
processing
 Many species of Bacillus are aerobic and
therefore cannot grow in a well evacuated
container
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Commercially canned foods have been spoiled by
bacillus species,especially in poor evacuated cans
aerobacilli or gas forming bacillus species have
been reported to cause spoilage of canned
peas,asparagus,spinach,peaches and tomatoes
SPOILAGE BY YEAST
Canned fruits,jams ,jellies, fruit juices , syrups
and sweetened condesed milk have been spoiled
by fermentative yeast with swelling of the cans
by carbon dioxide produced
 Film yeast may grow on the surface of jellied
pickled pork,repacked pickles or olives and
similar products but their presence indicates
contamination or lack of heat processing ,plus
poor evacuation
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SPOILAGE BY MOLDS
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Molds probably are the most common cause of the
spoilage of home canned foods which they enter
through a leak in the seal of the container
Jams , jellies, marmalades and fruit butters permit
mold growth when sugar concentration are as high as
70 % and in the acidity usually present in these
products
Some molds are fairly resistant to heat,especially
those forming tightly packed masses of mycelium
called sclerotia.
Byssochlamys fulva a pectin fermenting mold,has
ascospores that have resisted the heat processing of
bottled and canned fruits and have caused spoilage
SPOILAGE OF CANNED MEAT AND
FISH
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Canned fish and meat exhibits two chief types of
spoilage by:
bacillus species resulting in softening and souring
Clostridium species producing putrid swells
Less commonly bacilli may produced acid and gas and
swells the cans
Heat process given to Canned cured meats are
insufficient for sterilization therefore it may be
subjected to production of carbon dioxide,nitrogen
oxide or nitrogen gas from nitrate,sugars and meat or
they may subjected to putrefacation with gas
produced by Clostridium species
Such species ordinarily is prevented by adequate
refrigeration