Microorganisms can cause food deterioration by utilizing nutrients in food and producing enzymatic changes or new compounds that cause spoiling. To prevent spoilage, contact between microorganisms and food must be minimized by eliminating microorganisms from foods and understanding food preservation methods. Microorganisms are found in many places including soil, water, plants, equipment, food handlers, and air. They can be beneficial by aiding fermentation or pathogenic by causing foodborne illness or spoilage. Factors like pH, water activity, nutrients, and temperature affect microbial behavior in food.

1. College of Health Sciences
Dep. of Medical Laboratories
Food Microbiology Theory
3rd stage
Lecture 2
Dr: Shameeran S. Ismael
BVM & S, M.Sc Medical Microbiology(Parasitology),
PhD Molecular Parasitology

2. How microorganisms can cause
deterioration or damage of the food?
• When they utilize the nutrients of the food, it
involved changes in the food compound like
synthesis a new compound that cause spoiling
of the food or produced enzymatic changes
and contributing off-flavours by mean of
breakdown of product

3. How to prevent deterioration of the
food by microorganisms?
 Minimize the contact between microorganisms
and food
 Eliminate microorganisms from foods
 Understand about preservation of the food

4. Where are microorganisms?
• Soil & Water
• Plants/Products
• Utensils/Equipment
• Gastrointestinal Tract
• Food Handlers
• Animal Feeds
• Animal Hides
• Air & Dust

5. 5

7. Microorganisms are important in many
different ways:
• Pathogenic, or disease causing, microorganisms can
cause illness
• Spoilage microorganisms cause a food to smell, taste,
and look unacceptable
• Fermentation microorganisms produce a desired
food product
• Other microorganisms do nothing in foods
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8. What are the importance of
microorganisms in food?
A. Beneficial: some microorganisms can be considered
useful, if the changes due to their growth in foods are
deemed beneficial, for example, in terms of flavor,
texture, and appearance, they involved in the
following :
1. Food bio-processing
2. Food bio-preservation
3. Probiotics

9. B. Pathogenes: But some microorganisms can also be
able to spoil foods. From the point of view of sensory
rejection (deterioration), the spoilage microbiota
consists of microorganisms that can grow on a food,
causing undesirable changes, it cause:
1. Food borne disease
2. Food spoilage

10. A. Beneficial importance of
Microorganisms:
1.Food bio-processing:
Foods produce by using biological process. In this
process, food-grade microorganisms are used to
produce different types of fermented food using raw
materials from animal and plant sources (this process
known as “starter culture”).
Besides, microbial enzymes are also being used to
produce food and food additives

11. 2.Food bio-preservation
Is a food biological preservative by using antimicrobial
metabolites (taken from certain microorganisms in
order to control pathogenic and spoilage
microorganisms in foods).

12. 3.Probiotics
• Is a concentrated supplement of beneficial live cells
of bacteria (friendly bacteria) culture taken orally
intended to improve our health by promoting our
body’s natural immunity and improving digestion
system.

13. B. Pathogenes
1.Foodborne disease:
Is a disease cause by consumption of contaminate
during various stage of handling between production
and consumption by many pathogenic
microorganisms (bacteria, molds and viruses).

14. 2.Food spoilage:
Is a condition of contaminate food due to: growth of
microorganisms in food or the action of microbial
heat stable enzymes
• Microorganisms used food supply as a source of
nutrients by their own growth.
• Spoilage leads to wastage of food and economic loss.

15. Mechanisms of illness
• Infection
– Microorganisms are ingested and then cause illness
• Intoxication
– Toxins are produced by the pathogen, usually in
the food. When food is consumed, illness occurs.
– Even if microorganisms are killed, toxin can still
remain the food
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16. Common Foodborne Pathogens
• E. coli 0157:H7
• Salmonella spp.
• Staphyloccus
aureus
• Listeria
monocytogenes
• Campylobacter
jejuni
• Shigella spp.
• Norovirus
• Rotovirus
• Hepatitis A
 Cryptosporidium
parvum
 Giardia lamblia
 Entamoeba histolytica
 Cyclospora
Bacteria Viruses Parasites
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17. Spoilage Organisms
• Bacterial (hundreds of bacteria cause spoilage)
– Pseudomonas, Flavobacteria, & Enterobacter spp.
– Lactic acid bacteria
• Fungal
– Penicillium, Aspergillus, Fusarium, and Candida
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18. 80-90% of Foodborne Illnesses
from Bacteria come from just 4
Bacteria
• Campylobacter
• Salmonella
• Clostridium perfringens
• Staphylococcus aureus
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19. Factors Affecting Microbial
Behavior in Foods:
• There are two types of factor affecting in food
behavior:
a. Intrinsic factors: These are inherent in the food.
They include: pH, water activity, oxidation
reduction potential, nutrient content, antimicrobial
contents, biological structure
b. Extrinsic factors: Are factors external to the food
that affect microbial growth.

20. a.Intrinsic factors:
1. Hydrogen ion concentration (pH):
 Most bacteria grow best at neutral or weakly alkaline
pH usually between 6.8 and 7.5.
 Some bacteria can grow within a narrow pH range of
4.5 and 9.0, e.g. Salmonella
 Other microorganisms especially yeasts and molds
and some bacteria grow within a wide pH range, e.g.
molds grow between 1.5 to 11.0, while yeasts grow
between 1.5 and 8.5.

21. Microorganisms that are able to grow in acid
environment are called acidophilic
microorganisms. These microorganisms are able
to grow at pH of around 2.0
 Yeasts and molds grow under acidic conditions.
 Other microorganisms such as Vibrio cholerae
are sensitive to acids and prefer alkaline
conditions.
 Most bacteria are killed in strong acid or strong
alkaline environment except Mycobacteria

22. 2. Moisture content:
• The effect of moisture is in terms of water activity: -
the amount of free water in a food medium.
• The amount of free water is important for growth of
microorganisms.
• If there is lack of free water microorganisms will not
grow.
• Water activity is defined as the vapour pressure of a
food substance to that of water at the same
temperature. (Aw = VPFood/VPWater)

23. • The water activity of pure water is equal to 1.0
• Food products have a water activity of less than 1.0.
• A saturated salt solution has a water activity of 0.75.
• Salting and drying reduces the water activity of a
food product

24. • Growth of microorganisms is greatly affected by the
level of water activity (Aw) in the food.
• Inhibition of growth occurs if the water activity for
food is lowered beyond an organism’s minimum level
of water activity that is necessary for growth.
• Microorganisms have varying minimum water
activity requirements that supports their growth in
food

25. 3.Nutrients content of the food:
• Microorganisms require proteins, carbohydrates, lipids,
water, energy, nitrogen, sulphur, phosphorus, vitamins,
and minerals for growth.
• Various foods have specific nutrients that help in
microbial growth.
• Foods such as milk, meat and eggs contain a number of
nutrients that are required by microorganisms.
• These foods are hence susceptible to microbial spoilage.

26. 4.Antimicrobial substances :
• Antimicrobial substances in food inhibit microbial
growth.
• Various foods have inherent antimicrobial substances
that prevent (inhibit) microbial attack.
• Such inhibitors are like lactenin and anti- coliform
factors in milk and lysozyme in eggs.

27. 5.Biological structures:
• Some foods have biological structures that prevent
microbial entry. For example, meat has fascia, skin
and other membranes that prevent microbial entry.
• Eggs have shell and inner membranes that prevent
yolk and egg white from infection.

28. (b) Extrinsic factors
• Are factors external to the food that affect microbial
growth. They include:

29. 1.Temperature :
• The growth of microorganisms is affected by the
environmental temperatures.
• Various microorganisms are able to grow at certain
temperatures and not others.
•Bacteria can therefore be divided into the following
groups depending upon their optimum temperature of
growth:

30. i. Psychrophilic microorganisms :
• These grow best at about 20°C, also is called cold-
loving bacteria
• Psychrophilic bacteria can cause food spoilage at low
temperatures.
• Several of the microorganisms found in the soil and
water belong to this group.

31. ii. Mesophilic bacteria:
• These organisms grow between 25°C - 40°C, with an
optimum growth temperature close to 37°C (is an
organism that grows best in moderate temperature).
Such as Pseudomonas aeruginosa
• None of the mesophilic bacteria are able to grow
below 5°C or above 45°C.
• Most pathogenic bacteria belong to this group.

32. ii. Thermophilic bacteria:
• These grow at temperatures above 45°C. Often their
optimum growth temperatures are between 50°C and
70°C.
• Growth of some bacteria occur at 80 °C
• Bacteria in this group are mainly spore formers and
are of importance in the food industry especially in
processed foods.

33.  The effect of temperature on microbial growth also
depends upon other environmental conditions such
as:
• Growth factors in the nutrient medium
• pH of the food
• Water activity

34. 2. Concentration of gases in the environment:
This relates to the presence and concentration of
gases in the food environment.
• Various microorganisms require for growth, either
high oxygen tension (aerobic), low oxygen
tension (microaerobic) or absence of oxygen
(anaerobic).
• Some microorganisms may grow either in high
oxygen tension, or in the absence of oxygen
(facultative anaerobes).

35. Foods affected by various groups:
• Anaerobic or facultatively anaerobic
sporeformers are most likely to grow in canned
foods .
• Microaerophilic bacteria are most likely to grow
in vacuum packed foods since they have low
oxygen tension, while aerobic bacteria are likely
to grow on the surface of raw meat.
• Aerobic molds will grow in insufficiently dried or
salted products

36. 3. Relative humidity:
• Relative humidity is the amount of moisture in the
atmosphere or food environment.
• Foods with low water activity placed at high humidity
environment take up water, increase their water
activity and get spoiled easily.
• For example, dry grains stored in a environment with
high humidity will take up water and undergo mold
spoilage.

37. Prevention of Foodborne Illness
1.Cook all meat, poultry and eggs to at least 160F.
Other than spore-forming bacteria, all bacteria,
parasites and viruses are killed quite easily with
heating to 160F.
2. Avoid Cross-Contamination- Do not cross-
contaminate one food with another. Keep raw food
totally separated from cooked product.
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38. 3.Chill Foods- Keep foods cold. After cooking, chill foods
as rapidly as possible. Remember that cooking has
destroyed most of the bacteria but spore formers,
that are resistant to cooking may become very active
and can proliferate rapidly.
4.Cleaning-Wash fruits and vegetables and all foods
possible. In addition, continually wash work areas.
Use only treated or tested water.
5.Personal Hygiene- People working with foods should
wash their hands regularly, wear hairnets, plastic
gloves etc.
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39. Thanks for attention,,,,,,,,,,,
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Shameeran S. Ismael Parasitology theory.
health Sciences, 2020