How bacteria spoils food?

1. Presentation Topic ;
Food spoilage by Bacteria.
Presented By; Kashaf Ibrar.
Roll Number; 894.

2. Food spoilage by bacteria
Food spoilage ;
It is defined as damage or
injury to food redering it unsuitable for human
consumption.
 Food spoilage results when microbiological,
chemical or physical changes occur rendering
the food product unacceptable to the
consumer.

3. Bacteria;
are single celled microbes. The cell
structure is simpller and there is no nucleus or
membrane bound organelles. Bacteria cause
spoilage of food.

4. Microbial spoilage of food ;
Practically all kinds of
microorganisms are potential contaminants. The type
of food substance and the method by which it is
processed and preserved may favor contamination
by certain groups of microorganisms. Mist foodstuffs
serve as good media for the growth of many different
microorganisms.

5.  Given a chance to grow, the organismswill produce
changes in apperarance, flavour, odour and other
qualities of foods.
Degradation process of food;
It may be as follows;
1. Putrefaction.
2. Fermentation.
3. Rancidity.

6. 1. Putrefaction; in putrefaction, the skin
tissues of body eventually rupture and release
bacterial gas.
Protein food+proteolytic
microirganisms__________amminoacids+ammines
+ hydrogen sulfide+ammonia

7. 2. Fermentation;
is a metabolic process that produces
chemical changes in organic substrates through the action of
enzymes.
Carbohyhrate foods+carbohydrate fermenting
microorganisms________ acids+ alcohols+gases.

8. 3. Rancidity;
It refers to a water dependent process
in which bacteria use their enzymes such as
lipases to break down fats. It can be prevented by
sterillization.
Fatty foods+ lipplytic
microorganisms_________fatty acids+ glycerol.

10. Types of food spoilage.
 Microbial spoilage.
 Physical spoilage.
 Chemical spoilage.

11. Types of food in which spoilage
occur.
Spoilage occurs in:
 Fresh foods.
 Canned foods.
 Fresh milk.

12. Fresh Foods;
In fresh food, spoilage occur at any
stage. Enzymes can brinf destruction of polymers in
some foods and some chemical reactions like
oxidwtion and rancidity occurs and decompose fresh
foods.

14. Canned Foods;
• Canned foods because of
their heat resistance, spore formers (species of
clostridum and bacillus) constitute the most
important group of microorganisms in the
canning industry.
• The three most important types of
microbioligical spoilage of commercially canned
foods are;

15. 1. Flat sour spoilage.
2. Thermophillic anaerobe
spoilage.
3. Putrefaction.

17. Fresh Milk;
Milk is an excellent bacterological
medium. In fact , sterile skimmed milk is usec
routinely as a culture medium. Fresh whole milk
contains proteins(casein), carbohydrates (lactose)
and fat. All of these substrates can be dgraded
enzymatically by microorganisms. If the degradation
of these substrates is extensive , the accumulation of
end products will impart undesirable characteristics
to the milk.

18. • Some microorganisms can synthesize compounds
like pigments and slimes which also give
undesirable characteristics to the milk.
• A variety of microbes are found in milk.
Microbes of milk:
Salmonella,
Mycobacterium spp, E.coli, Staphylococcus
aureus, Bacillus cereus and micrococci etc.

19. Microbiological Examination of
Foods.
In the case of spoiled foods, it is possible to
identify the agent responsible for the spoilage;
having discovered tge agent, it may be possible to
trace the source of contamination and the
conditions which permitted spoilage to occur

20. Techniques used for microbiological
examination;
Two techniques are for the examination of
spoiled food. These are:
1) Microscopic Technique.
2) Culture Technique.
This examining of food is also useful to count
bacteria.

21. Microbes on spoiled food.
Bacteria:
 Coliforms.
 Fecal streptococci.
 Staphylococcus aureus.
 Salmonella spp.
 Shigella spp.
 Vibrio parahaemolyticus etc.
Protozoa:
 Entamoeba
histolytica.
 Giardia
lambia.
 Toxoplasma
gondii.

22. Viruses:
 Hepatitis A.
 Enterovirus.
 Pcurvovirus.
 Adenovirus.
Fungi:
 Aspergillus.
 Penicillium.
 Fusarium.
 Claviceps.

23. Preservation of food from
microbial spoilage.
Old Methods;
Today we associatefood
preservation with the refrigerator.
The ancient Egyptians and Romans were aware of
presevative effects of salting , drying and smoking.
 Salty preservation of food;
Accomplished by burning the food along the
shore,where seawater affected cure.

24.  Drying and smoking preservation of
food.
Placement of strips of fresh bison and
verison at the top of teepe or over a
campfire.
 Perishable foods preservation.
Perishable foids were stored in caves and
springs where low temprature prolonged the
preservation.

25. Modern Methods.
These include:
1) Asceptic Handling;
Food items undergoe
considerable or aseptic handling prior to preserve
food by methods of canning, freezing and
dehydration.
Example;
Egg shell__covering to protect egg

26. 2) High Temprature;
High temprature is one

27. the safest and most reliable methods of food
preservation.
Heat is widely used to destroy microrganisms in
food products in cans, jars or other type of
containers that restrict the enterance of microbes
after processing.
Steam under pressure;
Steam under pressure
such as in pressure cooker is most effective
method of higher temprature food preservation,
since it kill all vegetative cell and spores.

28. Key points in high temprature preservation;
Food preservation by heat requires;
 Knowledge of heat resistance of microorganisms
(particularly spores)
 Consideration of rate at at which heat penetrates
through foods of different consistencies and size
of packing containers.
 Consideration of time-temprature relationship to
kill microbes.

29. Research
Research is the field to helps to design specific
laboratory equipments to determine with
precision the heat resistance of various
bacterial species, particularly the
sporeformers.

30. Thank you.