This document discusses contamination and spoilage of canned foods. It describes how canned foods can spoil through three main mechanisms: survival of thermophilic bacterial spores due to inadequate heating; allowing germination of spores due to improper cooling or storage; and recontamination through leaks. It categorizes foods based on pH and outlines various types of biological spoilage caused by thermophilic and mesophilic bacteria, as well as by yeasts and molds. Common spoilage symptoms like gas formation, swelling, souring and black discoloration are also described.

1. CONTAMINATION AND SPOILAGE
OF CANNED FOOD
Sanjogta Thapa Magar
Food Microbiology

2. INTRODUCTON
 Canning is a method of preservation of food in which
food contents is processed and sealed in airtight
container such as metal,glass,thermostable plastic or
a multilayered flexible pouch.
 Heating is the principle factor to destroy most of the
microorganisms and the permanent sealing is to
prevent recontamination.
 Canning provides a shelf life typically ranging from
one to five years, although under specific
circumstances it may be more or less.

3. Foods that are canned on the basis of pH
1) Low acid foods : The foods that fall under th pH
5.0 to 6.8 such as meat,fish,poultry,dairy is
referred to as low acid foods.
2)Acids food : The foods with pH values between
4.5 and 3.7 are referred to as acids food.Eg:Fruits
such as pear,oranges,apricots and tomatoes.
3)High acids food : The foods with pH ranges
between 3.7 down to 2.3 such as pickled
products,fermented products,jams,jellies etc are
referred to as high acids food.

4. Canned food spoilage
Spoilage of canned food occurs by three ways:
1) Survival of spores of thermophilic bacteria due
to inadequate heating of canned food.
2) Allowing germination and growth of
thermophilic bacteria due to inadequate cooling
after heating or improper temperature storage.
3) Recontamination of microorganisms from
outside through leak in the container.

5. Types of biological spoilage of canned food
These are divided into two types;
Spoilage by thermophilic spore-forming bacteria
1.Flat sour
2. Thermophilic anaerobic spoilage
3. Thermophilic Anerobic Sulfide Spoilage
Spoilage by mesophilic spore forming bacteria
1.Spoilage by mesophilic Clostridium species
2.Spoilage by mesophilic Bacillus Species
Spoilage by non-spore forming bacteria
Spoilage by Yeast and Mold

6. Spoilage by thermophilic spore-forming
bacteria
1.Flat sour
•Occurs only in low acid foods (such as peas and
corn) and acid foods (such as tomatoes or tomato
juice) .
•Caused by the species of Bacillus such as Bacillus
coagulans and Bacillus stearothermophilus
•Souring due to acid formation
•No gas formation(no swelling of can)
•Source is usually plant equipment (e.g
blanchers),sugar and starch
•can be detected only by culture methods

7. Spoilage by thermophilic spore-forming
bacteria
Flat sour
B. coagulans-
• germinate at 43 °C and above
• Grows well between at 30-50 °C
• Homofermantative under anaerobic cond.
• Heterofermentative under aerobic conditions
B. stearothermophilus
• Optimum growth temp. is 55 °C

8. Spoilage by thermophilic spore-forming
bacteria
Flat sour causing organism detection by culture methods

9. Spoilage by thermophilic spore-forming
bacteria
2.Thermophilic Anerobic Spoilage
• Anaerobic Clostridium thermosaccharolyticum is
responsible
• H2 and CO2 gases produced at high temp.
• Swells the can and causes bursting
• Seen at medium acid can food products
• Sour fermentation and butyric or cheesy odor

10. Swollening of can

11. Spoilage by thermophilic spore-forming bacteria
3.Thermophilic Anaerobic Sulfide Spoilage
• No swelling, H2S production and rotten egg odor
• H2S produced by organism dissolves in the liquid and
reacts with tin
•Iron sulfide precipitation gives black color in food and the
inner wall of can
• Obligate anaerobes are responsible Disulfotomacullum
nigrificans
•They germinate and grow at thermophilic range
•Low acid canned foods (pears, corn , etc.)
•It indicates under processing, slow cooling or hot storage

12. Black spot on tin and on food

13. Spoilage by mesophilic spore-forming bacteria
1. Spoilage by mesophilic Clostridium species
•C. butyricum and C. pasteurianum are mostly
responsible
• Ferment sugar to produce volatile acids (butyric acid)
• Produce H2 and CO2 gases with swelling
• Also C. sporogenes, C. putraficiens, C. botulinum are
proteolytic and putrefactive organism(metabolizes
protein)
• Foul smelling compounds H2S, mercaptans, indoles and
ammonia
•Best grow in low acid canned food such as
meat,fish,corn,pea

14. Spoilage by mesophilic spore-forming bacteria
2.Spoilage by mesophilic Bacillus species
•Mesophilic Bacillus spore are not heat resistant as well as the
thermophiles.
•They survive in inadequate heated canned foods (in low acid home
canned foods) at 100 ° C.
•B. subtilis and B. mesentericus cause spoilage in poorly evacuated
cans.
•Mostly spoiled foods are Seafoods, meats and evaporated milk.
•B. polymyxa and B. macerans cause spoilage in canned peas,
asparagus, spinach, peaches and tomatoes.
•Usually spoiled food by contamination through leakage container.

15. Spoilage by Non-sporeforming Bacteria
• Non-spore forming bacteria survive in cans because of
mild heat treatment or leakage of the can
• Thermoduric nonspore forming bacteria can survive at
mild heat treatment
• Enterococcus, Microbacterium, Streptococcus
thermophilus, some species of Micrococcus and
Lactobacillus

16. Spoilage by Non-sporeforming Bacteria
• Non-spore forming bacteria survive in cans because of
mild heat treatment or leakage of the can
• Thermoduric nonspore forming bacteria can survive at
mild heat treatment
• Enterococcus, Microbacterium, Streptococcus
thermophilus, some species of Micrococcus and
Lactobacillus
• Acid forming Lactobacillus and Leucocnostoc spp.
Can survive in underprocessed tomato products, pears
and other fruits
• Heterofermentative – release CO2-swell the can by the
production of gas.

17. Spoilage by Non-sporeforming Bacteria
• Due to leakage of the can- Psedudomonas, Alcaligenes,
Flavonabacterium, proteus and other microorganisms
can also causes spoilage

18. Spoilage by Yeast and Mold
• Their presences in canned foods indicates under
processing,leakage,recontamination and poor
evacuation
• Fermentative yeast can spoil canned fruits, jams,
jellies, fruit juices, syrups and sweetened condensed
milk
• Swelling the cans by CO2 production
• yeast may grow on the surface of pickled meat,
pickles, olives and similar products

19. Spoilage by Yeast and Mold
• Molds are the most common food spoilage
microorganisms in home-canned foods due to high sugar
content (70%)
• Mold Species such as Sclerotia and Bysschlamys are
heat resistance and survive the mild heat treatment.
• Others may enter through leakage in the can
• Causes spoilage of high acid and high sugar food such as
Jams, jellies
• Penicillium and Aspergillus are most spoiling molds.
• Defects: moldy taste, odor, color fading and presence of
mold mycelia

20. Spoilage by Yeast and Mold
• Torula lactis and T. globosa causes blowing or
gaseous spoilage on sweetened milk (not heat
processed)
• Torula stellata causes spoilage in canned lemon and
grow at pH 2.5
• Heat resistant Molds Spoil acidic canned foods, fruits
• Most molds and yeasts are killed at 60 to 75 ° C for a
few min.
• Heat resistant molds produce ascospores that survive
at 85 ° C for 5 min or 90 ° C for 1 min

21. Spoilage of canned food by mold

22. Microbial spoilage in canned food

23. References
• Frazier, WC and Westhoff DC. Food Microbiology. 3rd.
New Delhi: Tata McGraw-Hill Publishing Company
Limited, 1986.
• Jay, MJ. Modern Food Microbiology. Ed. India. 3rd.
Delhi: CBS Publications and Distributions, 1987
• http://www.biologydiscussion.com/foods/spoilage-of-
canned-foods-with-diagram-microbiology/59052
• https://www.kullabs.com/classes/subjects/units/lessons/no
tes/note-detail/8753