This document summarizes spoilage of canned foods by various microorganisms. It discusses two types of spoilage - chemical and biological. Biological spoilage can be caused by thermophilic or mesophilic microorganisms and results in changes like putrefaction, acid production, gas production or blackening. Specific bacteria that cause spoilage are outlined, such as Clostridium botulinum in low acid foods and Bacillus coagulans in acidic foods. The document also categorizes microbial spoilage based on the acidity of different foods.

1. Assignment on Food and Dairy Microbiology
Topic – Spoilage of canned foods
Submitted by – Saloni Jain and Bhawna Sharma
Course – BSc.(H) Microbiology, II year
Submitted to – Dr. Salome John
Department of Microbiology
Ram Lal Anand College
University of Delhi

2. Introduction
 Canning or Appertization is important to ensure commercial sterilization of
some foods after processing through heat treatments.
 But there is always the possibility that a surviving organism may grow and cause
spoilage if environmental conditions permit.
 There are two types of spoilage –
1). Chemical spoilage – most important one is hydrogen swell .
this may occur due to -
a) high acidities of foods.
b) increasing temperatures of storage.
c) imperfections in interior and lacquering of cans.
2) Biological spoilage – this may occur due to –
a) survival of organisms after heat treatment, underprocessing.
b) leakage of the container.

3. Outer appearance of the unopened can
 The ends of a can of food is called flats, actually slightly concave.
 If pressure develops then it goes through the series of distortions, which are successively called as –
1). Flipper – one end is flat and other is convex.
2). Springer – one end is flat, other is bulged and if it is pressed on one side then other side
get pop out.
- Both flipper and springer may be due to poor exhaust, overfilling, denting
of the can, change in temperature.
3). Soft swell – both ends are bulged and can be dented by manual
pressure.
4). Hard swell – high pressure from inside and can’t be dented by hands.
- these both can be due to gas production from either a microbial or
chemical cause.
Fig. Different outer appearance of cans

4. Biological Spoilage
 Biological spoilage is classified on the two basis –
1. Types of microorganisms that causes spoilage –
a) Thermophilic bacteria
b) Mesophilic microorganisms
2. The kinds of changes produced in the food –
a) Putrefaction
b) Acid production
c) Gas production
d) Blackening – due to sulphide spoilage in canned peas and corns.
Fig. Swelling due to gas production. Fig. Blackening in canned corns

5. Spoilage by Thermophilic Spore Forming Bacteria
Type of Spoilage Bacteria Their effects on
different canned
foods
Flat sour spoilage
(means can remains flat during souring and
spoilage can’t be examined by outer
appearance, only acid produced which is
responsible for sour taste)
1. Bacillus coagulans
2. Bacillus stearothermophilus
- source is Plant Equipment
such as blanchers
1. Causes acid without gas
production in tomato or
tomato juices.
2. Food should be hot for its
spoilage.
TA Spoilage
( Thermophilic anaerobe that can’t produce
hydrogen sulphide but produces acid and
other gases)
1. Clostridium thermosaccharolyticum
( produces CO2 and H2 ,
causes bursting of can)
1. Sour or cheesy odor comes from spoiled
food.
Sulfide or “Sulfur Stinker” Spoilage
( H2S produced )
1. Desulfotomaculum nigrificans
( indicator of gross
under processing because
it is less heat resistant than
flat sour and TA bacteria )
1. H2S formed in canned peas or corn and
bluish-grey liquid also evident in canned
corn in which blackened germs and grey
kernels of corn float.

6. Spoilage by Mesophilic Microorganisms
Type of Spoilage Bacteria Their effects on
different canned
foods
Spoilage by Mesophilic
Clostridium Species
1. C.butyricum, C.pasteurianum
(Saccharolytic bacteria )
2. C.sporogenes, C.putrefaciens, C.
botulinum
( putrefactive anaerobes)
1. Butyric acid fermentation and CO2, H2
gas production in canned foods.
2. Putrefaction with the production of
malodor compounds such as ammonia,
mercaptans, skatole and indole.
Spoilage by Mesophilic Bacillus
Species
1. B.subtilis, B.mesentericus
2. B.polymyxa, B.macerans
1. Causes spoilage in home canned foods.
2. Causes spoilage in canned peas,
tomato etc.
( Produces acidic odors)
Spoilage by Non-Spore forming bacteria
( Includes thermoduric bacteria such as
Streptococcus thermophilus, Micrococcus,
Microbacterium )
1. Lactobacillus, Leuconostoc
2. S.faecalis
3. Herofermentative lactobacilli
4. Pseudomonas, Alcaligenes (non gas
forming)
1. Off odor and off flavor in frozen
concentrated orange juices due to acid
production and also spoiled tomato,
pears and other fruits.
2. Spoilage in canned hams.
3. Release CO2 gas to swell ccns.

7. Fig. Button like
appearance on
sweetened
condensed milk
Types of Spoilage Bacteria Their effects on
different canned
foods
Spoilage by yeasts 1. Fermentative yeasts
(Saccharomyces)
2. Film yeasts (Candida)
1. CO2 production in canned fruits,
jams, jellied, sirups and
condensed milk.
2. Grow on the surface of jellied
pickled pork and olives.
Spoilage by molds 1. Byssochlamys fulva ( pectin
fermenter, fairly resistant
to heat )
2. Aspergillus resens
3. Penicillium, Citromyces
1. Spoilage in bottled and canned
fruits.
2. Shows “button” like appearance
on sweetened condensed milk.
Fig. Mold growth on jam Fig. Mold spoilage on jam Fig. Different molds growth on PDA plates
(checked after a long period)

8. Classification of microbial spoilage on the basis
of acidity
Type of food Foods Involved Type of spoilage
Low acid (pH ≥5.3)
Medium acid (pH 5.3-4.5)
Meat and fish products, milk
vegetables like corn, beans, peas
1. Thermophilic flat sour group
2. Sulphide spoilage
3. Gas former, Clostridium
thermosaccharolyticum
4. Clostridium botulinum
Acid food (pH 3.7-4.5) Fruits, pears figs, tomato etc 1. Bacillus coagulans
2. Mesophilic spoiler
High acid (pH<3.7) Fruits like grapes, citrus, products
like sauerkraut, pickles etc
Non spore forming mesophiles,
yeasts, molds, lactic acid bacteria
Fig. Spoilage by
Clostridium botulinum
in vegetable (low acid
food).

9. Scheme for diagnosis of cause of spoilage of
canned foods