1. MICROBIAL GROWTH &
FOOD SPOILAGE

2. Contents
• Miracle of Bolsena
• BACTERIAL FOOD SPOILAGE
• Spoilage in Meat and Dairy Products
• Steps in Milk Spoilage
• Spoilage in fruits and vegetables
• Favourable conditions for Spoilage
• Spoilage in citrus fruits and juices
• Increase in Water activity aw

3. • FUNGAL FOOD SPOILAGE
• Fungal growth on tomatoes
• Fungal growth grains and corn
• Ergotism
• Fungal toxins
• Aflatoxins
• Mode of action
• Types of Aflatoxins
• Ingestion of Aflatoxins
• Fumonisins
• Type of fumonisins
• ALGAL TOXINS

4. Miracle of Bolsena
One of the most famous is the report of “blood”
on communion wafers and other bread, called
the “Miracle of Bolsena,” which occurred in
1263.
The mystery was eventually solved by
Bartolomeo Bizio in 1879, when he described
the red-pigmented bacterium responsible for
this phenomenon named Serratia marcescens.

5. BACTERIAL FOOD
SPOILAGE
Spoilage in Meat and Dairy Products
1. Proteolysis
2. Putrefaction
Steps in Milk Spoilage
1. Acid production by Lactococcus lactis subsp. lactis
2. Additional acid production associated with the growth
of more acid tolerant organisms such as Lactobacillus.
3. Yeasts and molds become dominant and degrade the
accumulated lactic acid
4. Protein-digesting bacteria become active, resulting in a
putrid odor and bitter flavour.

6. Spoilage In Fruits And
Vegetables
Example
Erwinia carotovora, bacteria that causes soft rots
by producing hydrolytic enzymes.
Favourable conditions for Spoilage
• high oxidation-reduction potential
• lack of reduced conditions permits
aerobes and facultative anaerobes to contribute to
the decomposition processes
Spoilage initiated by molds.

7. Spoilage In Citrus Fruits
And Juices
Food spoilage problems occur with minimally
processed, concentrated frozen citrus products.
Major spoilage can be caused by
Lactobacillus
Leuconostoc spp.
which produce diacetyl-butter flavours.
Saccharomyces and Candida can also spoil juices.

8. Increase In Water Activity aw
Concentrated juice has a decreased water activity (aw
-0.8 to 0.83), and when kept frozen at about -
10°C, juices can be stored for long periods.
Also, microorganisms in the frozen concentrated
juices can begin the spoilage process after addition
of water.
Ready-to-serve (RTS) juices present other problems
as aw values are sufficiently high to allow
microbial growth.

9. FUNGAL FOOD SPOILAGE
• Fungal growth on tomatoes
– Alternaria
– Cladosporium
– Fusarium
– Stemphylium
• Fungal growth grains and
corn
Molds mostly
– Penicillium (Green)
– Rhizopus stolonifer (Black)
(a) bread and (b) corn
(a)
(b)

10. Ergotism
Ascomycete Claviceps purpura causes ergotism,
a toxic condition.
• Hallucinogenic alkaloids produced by this
fungus can lead to
1. Altered behavior
2. Abortion
3. Death

11. Fungal Toxins
Carcinogens include the aflatoxins and fumonisins.
Aflatoxins
• Discovered in 1960, Aspergillus flavus
Mode of action
• These flat-ringed planar compounds intercalate
with the cells’ nucleic acids and act as frame shift
mutagens and carcinogens.
• Mostly Hepato-carcinogens

12. Types of Aflatoxins
A total of 18 aflatoxins are known. Aflatoxin B1
(most potent carcinogen)
Aflatoxins B1 and B2, after ingestion by lactating
animals, are modified in the animal body to yield
the aflatoxins M1 and M2.
Effects
1. Potent liver or hepato-carcinogens
2. Effects on immune competence
3. Growth and disease resistance in livestock and
laboratory animals.

14. Ingestion of Aflatoxins
The average aflatoxin intake in the typical
– European-style diet 19 ng/day
– Asian diets 103 ng/day
Risk factor
Individuals who have had hepatitis B have a 30-
fold higher risk of liver cancer upon exposure to
aflatoxins than individuals who have not had
this disease.

15. Fumonisins
The fumonisins are fungal contaminants of corn that
were first isolated in 1988. These are produced by
Fusarium moniliforme and cause
1. Leukoencephalomalacia in horses (also called
“blind staggers”—it is fatal within 2 to 3 days)
2. Pulmonary edema in pigs
3. Oesophageal cancer in humans
The fumonisins function by disrupting the synthesis
and metabolism of sphingolipids

16. Type of fumonisins
• There are at least ten different fumonisins; the
basic structures of fumonisins FB1 and FB2 shown.
• The fumonisins inhibit ceramide synthase, a key
enzyme for the proper use of fatty subtances in the
cell.
• Eucaryotic microorganisms can synthesize potent
toxins other than aflatoxins and fumonisins.

17. Fumonisin Structure; The basic structure of fumonisins FB1 and FB2 produced by
Fusarium moniliforme, a fungal contaminant that can grow in improperly stored corn. FB1,
R≐OH; FB2, R≐H.

18. ALGAL TOXINS
Contaminate shellfish and fin fish,
Causative agents
Dinoflagellates and Diatoms
Effects
– Amnesic
– Diarrheic
– Paralytic shellfish poisoning
These complex toxins, most of which are temperature
stable, are known to cause peripheral neurological
system effects

19. Any Q?