Post on 25-Apr-2022
Course instructor:
Dr.Tanushri Ghorai
Assistant Professor, COF, Dholi
Course Title: CANNING TECHNOLOGY Course Number: FPT:221
BFSc 2nd Year, 2nd Sem. (4th Semester)
Topic: Changes in canned foods and spoilage
Introduction
Change is the rule of nature and canned product is no exception to this rule.
Some changes make the product more acceptable.
For example, fish absorbs salt over a period of time from filling media and it will have better
taste than when it was just prepared.
Some changes are detrimental changes to the quality of the product.
However, if the detrimental changes are unacceptable to the consumer, such a change is
termed as spoilage.
In canning method of preservation, most of the detrimental changes arrested by excluding
oxygen from inside space of the can, destroying enzymes and microorganisms by heat.
Dr. Tanushri Ghorai Assistant Professor, COF, Dholi
Changes taking place during processing
Changes taking place in canned foods can be classified as
(a) those taking place during processing and
(b) those taking place after processing.
These can also be classified as those responsible for spoilage and that not responsible
spoilage.
Dr. Tanushri Ghorai Assistant Professor, COF, Dholi
Desirable changes
Absorption of salt by fish
Destruction of enzymes
Destruction of microorganisms
Denaturation of protein (Nutritive value does not change)
Softening of bones fins and scales and becomes edible;
Uniformity of taste and flavour throughout the pack (e.g. curry packs).
Dr. Tanushri Ghorai Assistant Professor, COF, Dholi
Undesirable changes
Loss of amino acid
Loss of vitamins
Fat oxidation rancidity
By adopting good manufacturing practice, these can be minimized
Dr. Tanushri Ghorai Assistant Professor, COF, Dholi
The chief defects and causes of spoilage may be listed as follows:
3. Physical: causes due to
a) Faulty retort operation
b) Under exhausting
c) Over filling
d) Internal vacuum too high (Panelling)
e) Use of cans of inadequate substances
f) Rough handling
4. Miscellaneous like: Rust, Damage et.c.,
1. Microbial spoilage: This may result due to
a) Under processing
b) Inadequate cooling
c) Leaker infection/Leakage through seams
d) Pre-process spoilage
2. Chemical spoilage
a) Internal corrosion giving rise to
hydrogen swells or pin holing
Dr. Tanushri Ghorai Assistant Professor, COF, Dholi
Changes during storage of processed cans
Due to exchange of various components of food, it becomes balanced with respect to
taste and flavour. This may take place in three months for certain foods and in some others it
may take even six months (e.g. acidity, saltiness, sugar) resulting in maturation of can.
During long storage period, the vacuum inside the can reduces and composition of head
space gases change.
Oxygen content reduces within a short time, hydrogen content increase in acid
foods, carbon dioxide also increases and in some foods ammonia and other gases
may be produced.Dr. Tanushri Ghorai Assistant Professor, COF, Dholi
Spoilage in canned foods
For any reason, if the food packed inside the can is not acceptable for human
consumption such a can is considered as spoiled can.
It is very difficult to ascertain whether the food is good or bad by external attributes
of a can.
When the food inside is spoilt, gases are generated which exert pressure on the can
ends and the cans bulge.
If the can ends are convex or bulged, it can be generally assumed that the cans are spoilt but
food inside such can need not be inedible on all occasions.
Spoilage of food inside the can need not be the only reason for bulging of cans.
Dr. Tanushri Ghorai Assistant Professor, COF, Dholi
Gaseous Spoilage
Can appears like Swelled or "bulging.
It is caused by spore-formers of the anaerobic or facultative anaerobic types.
Organisms found quite commonly are Clostridium welchii and Clostridium sporogens. and gas-forming
heat-resistant organism is Clostridium botulinum
Non-Gaseous Spoilage
There is no external indication of non-gaseous spoilage.
It is caused by aerobic spore formers, Bacillus cereus, B. mesentericus and B. vulgatus.
Storage at temperatures between 40 and 30 F. will greatly reduce the possibility of flat souring
Dr. Tanushri Ghorai Assistant Professor, COF, Dholi
Some bacteria (e.g. Bacillus stearothermophilus and B. coagulans) do not produce gas
when it spoils food.
In such cases, even though the food inside is spoilt, the cans appear good with flat ends.
In such cans the acidity will be high (low pH) and the food develops sour taste with
unpleasant odour.
Hence it is known as ‘flat sour spoilage’.
Dr. Tanushri Ghorai Assistant Professor, COF, Dholi
Bulged (swollen) cans
Bulged cans are classified into 4 categories.
1. Flipper
2. Springer
3. Soft swell
4. Hard swell
Dr. Tanushri Ghorai Assistant Professor, COF, Dholi
Flipper
In this, pressure inside the can is equal to the atmospheric pressure or inside
pressure is slightly higher than atmospheric pressure.
This excess pressure is equal to resistance of can end.
When such a can is hit on the table, the can end flips out and becomes convex.
Where the convex end is pressed it becomes flat again.
The reasons for this spoilage are
1. Under exhausting
2. 1st stage of H2 production
3. 1st stage of Microbial activity
4. Pre-processing spoilage of foodDr. Tanushri Ghorai Assistant Professor, COF, Dholi
Springer
If the inside pressure is more than in the case of flipper,
One end of the can remains permanently convex.
If this end is pressed down, the other end flips out.
The reasons for this spoilage are the same as in flipper.
Dr. Tanushri Ghorai Assistant Professor, COF, Dholi
Soft swell
Permanently convex can ends.
But when pressed by finger it get depressed but when the pressure is removed it
regains original bulge.
Dr. Tanushri Ghorai Assistant Professor, COF, Dholi
Hard swell
Permanently convex ends and do not get depressed due to pressure by
fingers.
Soft and hard swell are due to high pressure gases, more hydrogen production
or advance bacterial reaction.
Dr. Tanushri Ghorai Assistant Professor, COF, Dholi
Causes of spoilage in canned foods
To consider that the canned food is not spoilt, both the shape of the can and the food packed
inside should be in good condition.
There are many causes for the spoilage of cans which can be classified as follows
1. Physical causes
2. Chemical causes
3. Microbial causes
Dr. Tanushri Ghorai Assistant Professor, COF, Dholi
Physical causes
When the food can are lifted, moved from one place to the other loaded into baskets for
retorting or packed in boxes, they are likely to get damaged if carelessly handled.
The can loses its appearance.
If the dents are small, the food inside the can may not get affected.
If the dent is on or near the double seam, it may become lose and leads to leakage.
Dr. Tanushri Ghorai Assistant Professor, COF, Dholi
Physical damage can also occur due to sudden increase or decrease of pressure in the
retort and leads to panelling.
Panelling also may occur due to the too high head space.
The other reason is over packing of food as there is no space for expansion of can
contents during retorting.
This may lead to flipper or springer type of spoilage.
Moreover, over packing leads to under processing and the surviving bacteria can
grow inside and spoil the can (bulging).
Dr. Tanushri Ghorai Assistant Professor, COF, Dholi
Chemical causes
The chemical reaction between the food and the can materials (tin, iron) is the
important chemical cause for spoilage.
Due to this reaction hydrogen gas is produced and the metal ions are formed, as a
result metal content in the product increases.
When hydrogen gas is produced, the food inside the can may still be good but the
consumers may not accept it.
Excess heat processing also leads to non-enzymatic browning reaction resulting in
brown discolouration and charring.
Dr. Tanushri Ghorai Assistant Professor, COF, Dholi
Microbial causes
During pre-processing, that is during the preparation of raw material or after
packing but before retorting, the bacteria present in food may spoil it to some extent.
Though heat processing kills the bacteria, the quality of food can be improved.
If the extent of spoilage is less, it goes unnoticed,
But if the extent is more, then it is called as pre-process spoilage.
In pre-process spoilage pH changes to some extent, gases are produced and the food
becomes soft.
Dr. Tanushri Ghorai Assistant Professor, COF, Dholi
If there is power failure or for any other reason, half completed cans, filled and seamed
cans held up for a long time before heat processing, pre-process spoilage occur.
In such cans flipper or springer may be observed.
It may not lead to hard swell.
In such cans, living microorganisms or their spore may not be found.
But microscopic examination show more dead cells.
The quality of food inside may not be good.
By minimising delay in each stage and from one stage to the other and also by observing
good hygiene and sanitation practices, this type of spoilage can be minimised.
Dr. Tanushri Ghorai Assistant Professor, COF, Dholi
Under-processing
Under-processing may be due to several reasons listed below.
1. Inadequate thermal process to kill the most significant microorganisms.
2. Contamination by highly heat resistant organism not usually present in the food.
3. Unusually high level of contamination by usual contaminant microorganisms.
4. Faulty retort operation.
5. Improper working of instruments fixed to the retorts.
6. Air inside the retort due to incomplete venting.
7. Changes in consistency, improper fill with respect to higher weight of solids, solid-
liquid ratio, head space etc.
8. Low initial temperature of the product. Dr. Tanushri Ghorai Assistant Professor, COF, Dholi
Post-processing spoilage
Another microbial spoilage is ‘post-processing spoilage’.
In spite of conducting preparation, processing and can cooling in a proper way, sometimes heat
processed cans spoil due to entry of microorganisms into the can.
Leakage of cans is the only reason for this kind of spoilage.
The reasons for this spoilage are
* Loose double seam
*Physical damage at the double seam
Dr. Tanushri Ghorai Assistant Professor, COF, Dholi
As water sucked into the can while can cooling, microorganisms present in water get
into it and spoil the food.
Sometimes, leaked cans close by itself and due to gases produced inside, the
cans bulge.
Such a spoilage is called as ‘leaker spoilage’.
In such cans, a variety of microorganisms (mixture of non-spore formers or spore
formers) are present.
Addition of 4-7 ppm of free chlorine in can cooling water minimises this spoilage.
In air cooling this spoilage is much less than in water cooling.Dr. Tanushri Ghorai Assistant Professor, COF, Dholi
Other causes of spoilage
Rusting of cans, an important cause for major loss in canning industry.
Storage in humid atmospheric conditions, salty breeze, corrosive fumes,
fluctuations in storage temperatures lead to rusting of cans.
Careless handling of cans, rusted trolleys, heavy embossing of can ends for coding and
over cooling of cans are some of reasons for rusting.
Corrosive label pastes or adhesives.
Bad storage conditions (dust, storing on the floor, leakage from top layer of cans etc).
Dr. Tanushri Ghorai Assistant Professor, COF, Dholi