2. Introduction:
• Canning is a method of preservation of food in which
the food contents is processed and sealed in airtight
containers (of metal, glass, thermo stable plastic, or
a multi- layered flexible pouch).
• Heating is the principle factor to destroy the
microorganisms and the permanent sealing is to
prevent re-infection.
3. Foods that are canned:
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.
Acid foods: With pH values between 4.5 and 3.7. Fruits
such as pear, oranges, apricots and tomatoes fall in this
class.
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.
4.
5. Spoilage in Canned Foods:
Spoilage of canned food occurs by:
• Survival of spores of some thermophilic bacteria
during heating of canned food.
• Recontamination of microorganism from outside
through leak in the container.
6. Spoilage of canned food according to the
condition and content of the can:
• Swell: bulging by internal pressure due to gas generated by
microbial or chemical activity.Either hard or soft swell.
• Flipper: normal appearance,oneend flips out when the can
struck against a solid object but snaps back to the normal
under light pressure.
7. 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.
8. Spoilage of canned food according to the cause:
Microbial spoilage:
Major spoilage by Thermophilic spore forming Bacteria:
(a)Flat Sour Spoilage:
• mainly occurs in low acidic foods.
• caused by the species of Bacillus such as Bacillus
stearothermophillus ,Bacillus coagulans.
• the can is not swollen by gas production.
9. (b) Thermophilic anaerobic (TA) Spoilage:
• caused by thermophilic anaerobe not producing hydrogen
sulfide.
• Clostrodium thermosaccharolyticum is the main organism
involved.
• produce acid and gas in food.
• spoiled food produce sour and cheesy smell.
10. Chemical Spoilage:
(a) Hydrogen swell:
• Formation of hydrogen gas due to internal corrison or scratch.
• Occur mainly in acidic foods (canned fruits).
• Rarely in canned meat but seen in canned sardines.
11. Contd…
• Not related to fermentation or bacterial spoilage.
• Can show varying degree of bulging.
• Quite harmless but undifferentiated from swell of spoiled
can.So, it is rejected.
12. (b) Sulphur strinker spoilage:
• Desulfotomaculum nigricans is the main oragnism
involved.
• spore of this organism is usually less heat resistant than
those of flat sour and TA bacteria .
• therefore, spoilage by this organism indicates
inadequate heat treatment during canning.
13. Contd….
• organism produced hydrogen sulphide that reacts with a tin of
canned to from black spots of fees in food and the inner wall
of the can.
• Hydrogen sulphide produced give putrid odour which is
evidenced when the can is opened.
14. Classification of microbial spoilage on the basis
of acidity:
Type of food Foods Involved Type of spoilage
Low acid pH > 5.4
Medium acid pH: 5.3-4.6
Meat and fish products
milk, vegetables like corn,
lima beans, peas, meat and
vegetable mixers.
i) Thermophilic flat sour
group. (Bacillus
sterothermophilus, B.
coagulans).
ii) Sulphide spoilage
(Clostridium nigrificans, C.
bifermentans).
iii) Gas formers (Clostridium
thermosaccharolyticum).
iv) Mesophilic spoilage like
putrefactive anaerobe.
v) Spoilage and toxin
production by Clostridium
botulinum.
15. Acid food pH: 3.7-4.6 Fruits, pears, figs, tomato
etc.
i) Thermophilic
spoiler Bacillus coagulans
ii) Mesophilic spoiler B.
polymyxa, Clostridium
pasteurianum,
C. butyricum,
Lactobacilli etc.
High acid pH<3.7 Fruits like grape fruit,
citrus, rhubarb etc and
products like sauerkraut,
pickles etc.
Non-spore forming
mesophiles, yeast, mould
and/or lactic acid bacteria.
16. Spoilage by Yeasts:
• Presence of yeasts is the result of either gross
underprocessing or leakage.
• Cause swelling by the production of carbondioxide.
• Canned fruits, jams, jellies, fruits juice etc have been spoiled
by fermentative yeasts like Saccharomyces cerevisiae,
Saccharomyces pastorianus.
•
17. Spoilage by Molds:
• Aspergilus and Penicillium are most spoiling organisms.
• Molds are more common in home canned foods where
heating as well as sealing is not under total aseptic conditions.
• can grow at high sugar concentration.
• Acidification is the preventing method to prevent growth of
molds.
