changes in canned foods and spoilage

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.


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).


Undesirable changes

Loss of amino acid

Loss of vitamins

Fat oxidation rancidity

By adopting good manufacturing practice, these can be minimized


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


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.


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


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’.


Bulged (swollen) cans

Bulged cans are classified into 4 categories.

1. Flipper

2. Springer

3. Soft swell

4. Hard swell


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.


Soft swell

Permanently convex can ends.

But when pressed by finger it get depressed but when the pressure is removed it

regains original bulge.


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.


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


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.


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).


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.


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.


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.


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


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).


changes in canned foods and spoilage

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