This document discusses the microbiology of meat, fruits, and vegetables. It notes that meat provides nutrients for microbial growth between a pH of 5.6-7.4. Spoilage microorganisms commonly found on meat include various pathogenic and spoilage bacteria as well as molds. Key factors that affect meat spoilage are water content, redox potential, pH, and temperature. Both aerobic and anaerobic conditions can lead to spoilage through surface slime, color changes, and off flavors/odors. Similarly, fruits and vegetables are susceptible to spoilage by molds and bacteria through various rots and softening if the skin is broken and sanitary conditions are poor.

1. MICROBIOLOGY OF MEAT
MICRO-509

2. Microbiology of meat
 Meat is easily spoiled by microorganisms
because it contains a lot of nutrient, growth
factors etc. the pH for meat is the range of 5.6-
7.4.
 Microorganism for soil, water and manure
make up the dominant flora of meat. During
slaughter, the external surface of the animal
may contaminate the meat by direct contact
through the above sources and equipment,
personnel and slaughtering area.

3.  Bacteria generally found in meat:
a) Pathogenic microorganism
eg: Brucella, Salmonella, Streptococcus,
Mycobacterium tuberculosis, Clostridium
b) Spoilage microorganisms
eg: Achromobacter, Pseudomonas, Bacillus
and Staphylococcus
c) Molds
eg: Aspergillus, Mucor, Penicillium

4. Factors affecting the spoilage of meat
a. Water content
b. Redox potential
c. pH value
d. temperature

5. a) water content
 Meat has high water content with dissolved
substances such as glycogen, lactic acids and
amino acids.
 All these substance can cause microbial
growth which can lead to early spoilage.

6. b) Redox potential
 Has a big influence on microbes.
 Tissue respiration continues after death and uses
up oxygen present and produce CO2 .
 Finally oxygen tension will fall (Eh negative).
 The inner side of meat becomes anaerobic;
together with the production of lactic acids.
 The bulk of meat becomes anaerobic except on
the surface. At the surface, aerobic flora and
inside meat, anaerobic flora predominates. But,
these microorganisms do not grow readily at low
temperature, therefore little growth may be
observed.

7. c) pH value
 pH value of the meat is between 5.5-7.4.
Acidic pH (5.5) not suitable for growth of many
types of microorganisms.
 pH of meat depends on amount of lactic acid
produced after death.
 The more acid produced the lower the pH. But,
the amount of acid depends on the amount of
glycogen in the muscle at death.

8. i. If animal is exercised before slaughter, the
glycogen is low, little lactic acid produced and
the pH of carcass is relatively high. Muscle will
be dry and firm in texture and dark in color.
ii. If non-exercised animal is stimulated before
slaughter such as stress, glycogen will rapidly
turn to lactic acid and low pH is approached
before tissue has time to cool. This cause
denaturation of some, muscle protein. Meat will
become pale, soft and exudative.

9.  The type and spoilage of meat is determined by:
 Initial numbers present
 pH value of meat – if pH > 6.0. Microorganisms
can grow fast. Meat will putrefy mainly due to
Pseudomonas and Aeromonas type.
 Two types of spoilage:Aerobic condition
Anaerobic condition

10.  Aerobic condition
a) Surface slime
b) Colour change
c) Off flavors and odours

11. a) Surface slime
 Accumulation of microorganism on meat surface cause by gram-
negative rods such as Pseudomonas and Achromobacter
b) Colour change
 Occur more quickly if stored in oxygen.
 Red spots on meat – pigments of Serratia
 Yellow spots – pigments of Flavobacterium
 Green spots – pigments of Pennicilium
 White spots – pigments of Rhizopus

12. c) Off flavors and odours
• Undesirable odor and taste called taint are caused by many bacteria due to
production of volatile acids such as formic acid, acetic acid, butyric acid etc.
• Actinomycetes give musty or earthy flavor.
It can also due to production of compounds such as amines, ammonia
caused by degradation of amino acid by proteolytic bacteria such as
Pseudomonas spp whereas Actinomycetes will give an earthy odour.

13. Anaerobic condition
a) Putrefaction
•It refers to the anaerobic decomposition of protein with production of
offensive smelling compounds such as H2S, mercapatans, indole,
skatole etc.
•It is usually caused by Clostridium species but species
of Pseudomonas proteus and Alkaligens may cause putrefaction
b)
Souring
Can be microbial and biochemical. Microbial souring is due to
the formation of fatty acids and lactic acids, with no putrefaction.
E.g. Clostridium, Bacillus

14. Microbiology of fruits and
vegetables
 25% of fruits and vegetables are spoilt before
harvesting because of infection and disease.
 Spoilage after harvesting is due to
mishandling, over-ripening etc. Skin becomes
soft, makes it easier to be infected by
microorganisms.

15. Fruits
Fruits are covered with skin/shell for:
a) Natural protection from microbial infection.
b) Minimize moisture loss to environment.
c) Stabilize enzymatic changes.
 Healthy fresh fruits are free from microorganisms.
Once skin is broken e.g. insect sting, it will become
infected especially if put in place where sanitary
condition is not satisfactory.

16.  The kind of microorganisms in fruits depend on various
factors:
a) Characteristics of fruit – soft ones more prone to infection.
b) Nutrient content – sugar and acid.
c) Climatic condition.
 Bacteria do not play important role in fruit spoilage due to
acidity of fruits.
 Mold spoilage usually more significant.
 Yeast usually initiate spoilage then later taken over by molds.
Spoilage by yeast is not extensive.

17. Spoilage of fruits:
 Blue mold rot: Penicillium expansum
 Black mold spoilage: Aspergillus spp
 Green mold spoilage: Cladosporium spp.
 Bacteria soft rot: Xanthomonas, Erwinia and
Pseudomonas

18. Vegetables
 Vegetables are easily spoilt, just like fruits.
 Examples: 40%tomatoes are already spoilt before
consumption.
 Through genetic engineering, new hybrid of tomato is
produced to reduce spoilage. Example: flav sav tomato.
 Vegetable contain more available water and less
carbohydrate or fat content compared to fruits. High pH and
the less acidic content are favoured by bacteria.

19. Spoilage of vegetables:
 Bacteria soft rot – the vegetables part
becomes soft and moist. These bacteria
produce pectinase which can hydrolyze pectin
such as in tomato, garlic, celery etc.
 Mold spoilage to vegetables:
🞑 Grey mold rot – Botrytis spp.
🞑 Sour rot – cause formation of acid. Geotricum
candidum.