microorganisms associated with food

1. MICROORGANISMS IN FOOD

2. Introduction
• Except for a few sterile foods, all foods harbor one or
more types of microorganisms.
• Some of them have desirable roles in food, such as
1. in the production of naturally fermented food,
whereas
2. others cause food spoilage and foodborne diseases.
• To study the role of microorganisms in food and to
control them when necessary, it is important to
isolate them in pure culture and study their
morphological, physiological, biochemical, and
genetic characteristics.

3. Importance
Good (desirable) Bad (undesirable)
1. Food bioprocessing
2. Food biopreservation
3. Probiotics
1. Food borne disease
2. Food spoilage
The importance of microorganism in food

5. a) Moulds
Eukaryotics cells*
Multicellular
Non motile, filamentous and branched
Compose of large numbers of filaments called hyphae
which are aggregated and called mycelium
Reproduction occurs from spore formation
Eg: penicillium spp
Morphology and structure of microorganisms

6. Aspergillus oryzae :
hydrolyze starch in sake
production
Aspergillus niger : citric
acid production.
Geotrichum candidum-
Often grow on dairy
products
Penicillium roquerfortii
and Penicillium
camembertii are used in
cheese production
Mucor rouxii cause
spoilage of vegetables

7. b) Yeasts
- Eukaryotic cells*
- Unicellular
- Oval, spherical or elongated
- Non motile, can see budding formation
• Eg: Sacchromyces cerevisiae
• Eukaryotic cells* - generally are:
Larger cells (20 to 100µm)
Cells have rigid cell walls and thin plasma
membrane
Cytoplasm contains organelles such as
Morphology and structure of microorganisms

8. S.cerevisiae is employed
in many food industries
e.g bread manufacturing,
wines, alcohol etc.
S.fragilis and s.lactis is
important in milk and
milk products because
they are common
spoilage microorganism
Cause rancidity in butter
and dairyproducts e.g:
Candida lipolytica
Genus Rhodotorula- Red,
pink or yellow yeasts
may caused
decolouration on food
such as in meat, fish and
sauerkraut.

9. c) Bacteria
-Prokaryotic cells
-Unicellular
- Three morphology forms:
Spherical (cocci) – eg: streptococcus spp
Bacilli (rod) - eg: bacillus spp
Curved (coma) – eg:
-Can be motile or non motile
-The cytoplasmic materials are enclosed in a rigid
wall on the surface and a membrane beneath the
wall
- The organelle does not enclosed in a separate
membrane
Morphology and structure of microorganisms

10. • Foodborne diseases (Bacillus cereus) and food
spoilage in canned products (Bacillus coagulans
and Bacillus stearothermophillus)
• Pathogenic org.’s e.g.: Clostridium botulinum and
Clostridium perfingens
• Escherichia coli used as an indicator ofsanitation
• Food bioprocessing: L. bulgaricus, L. lactis.
• Probiotics: L. Acidophilus
• S. aureus are frequently involved in foodborne
diseases

11. d) Viruses
- Non cellular entities
-Most important: bacteriophages (bacterial viruses)
-Virus contain nucleic acid (DNA and RNA) and
protein
Morphology and structure of microorganisms