This document discusses meat and the conversion of muscle to meat after an animal's death. It defines meat as the flesh of an animal used for food, which is mostly muscle tissue. After death, the muscle undergoes physical and chemical changes over hours or days as homeostasis is lost, known as rigor mortis. The time for rigor mortis varies by species from less than half an hour for chicken to 6-12 hours for beef. The document also discusses factors that influence microbial growth on meat and causes of meat spoilage under aerobic and anaerobic conditions.

2. The flesh of an animal, typically a
mammal or bird, which is used as
food. It is mostly the muscle tissue of
an animal.
WHAT IS MEAT
?

3. CONVERSION OF MUSCLE TO MEAT
■ Muscles do not suddenly eliminate all living functions.
■ A number of physical and chemical changes occur over a
period of hours or days (RIGOR MORTIS).
■ While homeostasis is maintained within living muscle
homeostasis is lost during the conversion of muscle to meat.

4. STEPWISE CONVERTION OF MUSCLE TO MEAT
DEATH BLOOD FLOW
STOPS
NO ATP
PRODUCTION
ANAEROBIC
GLCOLYSIS
STILL PERSISTS
ATP
RELEASED
FROM
STORED
GLYCOGEN
ENERGY FOR
CONTRACTION
LACTIC ACID
PRODUCTION
CALCIUM
RELEASE
ACTIN AND
MYOSIN IS
LOCKED
PERMANENT
CONTRACTION
RIGOR MORTIS
COMPLETE
NO OXYGEN SUPPLY
THROUGHOUT THE
BODY

5. TIME TO THE ONSET OF RIGOR MORTIS
FOR VARIOUS EDIBLE MEATS
SPECIES TIME HOURS
Beef 6 to 12 Hours
Lamb 6 to 12 Hours
Pork 1/4 to 3 Hours
Turkey <1 Hour
Chicken < 1/2 Hour
Fish <1 Hour

6. TWO TYPES OF UN-
ACCEPTABLE MEATS
1. PSE
(PALE, SOFT, EXUDATIVE) type
2. DFD
(DRY, FIRM & DARK) type

7. 1. PSE (PALE, SOFT, EXUDATIVE)
► 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 causes denaturation of some muscle protein.
► Meat will become pale, soft, and exudative (PSE
condition).

8. 2. DFD (DRY, FIRM, AND DARK)
► 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
colour (DFD condition).

9. CHEMICAL COMPOSITION OF TYPICAL ADULT MAMMALIAN MUSCLE
AFTER RIGOR MORTIS

10. COMPONENT % WET WEIGHT
SOLUBLE NON-PROTEIN NITROGEN 1.65
CREATINE 0.55
INOSINE MONOPHOSPHATE 0.30
NAD/NADP 0.30
NUCLEOTIDES 0.10
AMINOACIDS 0.35
CARNOSINE, ANSERINE 0.35
INORGANIC 0.65
TOTAL SOLUBLE PHOSPHORUS 0.20
POTASSIUM 0.35
SODIUM 0.05
MAGNESIUM 0.02
OTHER METALS 0.23
VITAMINS (MOST B-VITAMINS PRESENT IN USEFUL AMOUNTS)
CHEMICAL COMPOSITION OF TYPICAL ADULT MAMMALIAN MUSCLE
AFTER RIGOR MORTIS

11. WHY IS MEAT AN IDEAL MEDIUM FOR
MICROBIAL GROWTH ?
 High in moisture (70% water ), water activity (aw)
close to 0.99.
 Rich in protein (nitrogenous food) - 18 – 20 %
protein.
 Minerals necessary for growth.
 Sufficient carbohydrates.
 Favorable pH (5.6 -7.4).

12. SIGNIFICANCE &
IMPORTANT FACTORS
WHICH INFLUENCES THE
GROWTH OF
MICROORGANISMS

13. 1. REDOX POTENTIAL
 Redox potential is a major influencing factor .
 the oxygen tension and redox potential in living muscle are high.
At death both gradually fall, leading to anaerobic production and
accumulation of lactic acid.
The acidity so developed greatly diminishes tissue metabolism
(tissue metabolism continues for several days even at low
temperature)
 The bulk of meat becomes anaerobic within a few hours post
mortem.

14. CONTINUED…
 Freezing, cooking, or salting inhibits tissue respiration but
reducing environment already created maintains anaerobic
conditions within any piece of meat(~ 10mm thick) except on the
surface.
Aerobic flora develops on the surface and anaerobic or facultative
flora within the tissue. But majority of them scarcely develop in
chilled meat even after long periods.
 Mincing reaerates meat but anaerobic condition is reestablished
gradually if minced meat is packed again.

15. 2. pH INFLUENCES MICROFLORA TO GREAT
EXTENT.
 THE ph OF MEAT RANGES FROM 5.0 to 7.0.
 Neutral ph favours pathogenic and spoilage organisms.
 Ph values below 5.5 are unfavorable to the growth of
many important bacteria.
 Low ph in combination with low temperature almost
prevents bacterial growth.
 Low ph in combination with curing salts is effective
against bacteria found in cured meats.

16. 3.WATER CONTENT
Meat has high water content with
dissolved substances such as
glycogen, lactic acid, and amino
acids.
All these substances can cause
microbial growth which can lead to
early spoilage.

17. 4.TEMPERATURE
Temperature changes result in structural
transformations that affect the texture,
juiciness, and mouth feel of the meat.
The higher the temperature of the heat applied
to the meat, the faster these changes happen.
Contributes to spoilage.

18. CONTAMINATION SOURCES
1. Only healthy animals must be used for meat.
2. Contamination occurs from the following sources:-
— Contact with hide, skin or feet
— Stomach and intestinal contents
— Processing plant and equipment
— Hands and clothing of personnel
— Water used for washing
— Air in the processing and storage areas
3. Contamination may occur during every operation.
4. Extent of contamination reflects the standards of hygiene and sanitation.
5. The initial flora is mainly determined by surface contamination received during
the primary operations of meat processing (SLAUGHTER, DRESSING, CHILLING,
AND CUTTING).

19. INITIAL MICROFLORA
► The tissue of healthy animal contains few microorganisms. (Exceptions:
external surfaces, gastrointestinal and respiratory tract which contains high).
► Defense mechanism effectively controls infectious agents in live animals.
► Defense begins to fail after slaughter.
► Major sources of contamination:
■ Location of the farm
— Temperature – tropical or temperate
— Soil condition – wet and muddy; dry and dusty
■ Method of transport.
■ Holding conditions in the slaughter house.
■ Faecal matter – influenced by dietary factors.

20. CONTAMINATION IN
MEAT PROCESSESING

21. 1. SLAUGHTER
► Generally by delay in the removal of viscera, the
muscle is contaminated with intestinal flora;
which leads to spoilage deep within the muscle.
► Aseptically handled tissue is relatively sterile.
► Contamination through the blood circulation is
not significant.

22. 2. DRESSING
► The first major source of contamination is
from the skin or hide.
► Normal flora of skin includes:-
Staphylococcus, micrococcus, pseudomonas,
yeasts and molds and organisms of faecal and soil
origin.
► Further contamination occurs from knives,
hands, and clothing of the workers and the
water used for washing.

23. ►Suitable sprays may diminish surface contamination several folds
– water pressure, temperature, and nozzle design are also
important.
►The levels of contamination is usually lower in the body cavities
than in the external surface.
►Levels of microorganisms on beef carcasses at the end of
hygienic dressing:-
— VIABLE AEROBIC BACTERIA 103 - 105/cm2; PSYCHROTOPHS
<102/cm2 ; COLIFORMS 10-102/cm2.
►Sheep carcasses usually have slightly higher counts:-
— VIABLE AEROBIC COUNT 103-106/cm2; PSYCHROTROPHS
<103/cm2.
CONTINUED…

24. 3. CHILLING
► Chilling retards microbial growth.
► Fast chilling at low-temperatures and low-humidity is
more effective.
► Psychrotrophs overgrow mesophiles.
► Time has more effect than temperature.
► Cooling at ambient temperature favours growth of
mesophiles including pathogens.
► Carcass should be immediately chilled to <3˚c.

25. 4. CUTTING AND BONING
► Meat receives excessive handling during cutting, boning, and
packaging.
► Fresh surfaces are exposed during this process.
► Meat is more susceptible to the effects of contamination.
► Temperature, length of time, cleanliness of surfaces, tools etc.
Affect the microflora.
► Mesophiles gradually build-up.
► Contaminated with bacteria of human origin.
► Enteric viruses of human and animal origin are also found.

26. WHY DO WE STUDY
MICROBIOLOGY OF MEAT?
 Meat and meat products, serve as excellent growth media for a
variety of bacteria.
 Although the outer surface of meat is generally covered by
microorganisms, the inner part of the meat contains few
organisms.
 The contamination in meat comes mostly from external sources
during :-
— Bleeding
— Handling
— Processing

27.  Microorganisms that contaminate meat vary widely.
 The most common cause of meat spoilage is the deterioration of
meat caused by micro-organisms (bacteria, yeasts, and molds).
 All meat poisoning is caused by post slaughtering contaminations.
 So it is very important to create awareness on these ubiquitous
microorganisms.
 The main area of concern is:-
— Any tissue near the surface of a carcass.
— Whole muscle cuts.
WHY DO WE STUDY
MICROBIOLOGY OF MEAT?

28. SPOILAGE
OF
MEAT

29. Spoilage of meat is considered
under:-
Under Aerobic conditions
Under Anaerobic conditions
•The spoilage of meat is determined
by initial numbers present.
•pH of meat.

30.  Under aerobic condition
1.Surface slime
 Accumulation of microorganisms on meat surface
caused by gram negative rods such as Pseudomonas
and Achromobacter.
2.Colour change
 Occurs more quickly if stored in oxygen.
 Red coloured meat (oxidized myoglobin) can change to
brown due to the production of oxidizing compounds
such as peroxides and H2S from bacteria E.g-
Leuconostoc spp.

31.  Red spots on meat- Pigments of Serratia.
 Yellow spots – Pigments of Flavobacterium.
 Green spots- Pigments of Pennicilium.
 White spots- Pigments of Rhizopus.
3.Off flavor and odour
 Due to the formation of fatty acids on meat surface
such as formic, butyric, and propionic acid.
 It can also occur due to the production of compounds
such as amines, ammonia caused by degradation of
amino acids by proteolytic bacteria such as
Pseudomonas spp.
 Whereas Actinomycetes will give an earthy odour.

32. 4.Rancidity
 Caused by some Lipolytic bacteria and moulds.
 Under anaerobic condition
1.Putrefaction
 Breakdown of proteins with the formation of foul
smelling compounds such as mercaptans, H2S, indole,
amine and others.
 This occurs due to the presence of culprit organisms
such as Proteus, Clostridium and Bacillus.

33. 2.Souring
 Can be microbial and biochemical.
 Microbial souring- Due to the formation of fatty acids
and lactic acids, with no putrefaction. E.g- Clostridium,
Bacillus.
 Biochemical souring- Results from the utilization of
lactose and other sugars and the production of acids.
 Normally occur underneath the casing of meat
products.
3.Taint
 A trace of a bad or undesirable substance or quality.

34. Different kinds of meat and their spoilage organisms
MEAT
Food Types of Spoilage Spoilage Microorganisms
Fresh/chilled
Putrefaction
Clostridium, Pseudomonas, Proteus,
Alcaligenes, Chromobacterium
Souring
Chromobacterium, Lactobacillus,
Pseudomonas
Cured
Moldy Penicillium, Aspergillus, Rhizopus.
Souring Pseudomonas, Micrococcus, Bacillus
Greening
Lactobacillus spp., Streptococcus,
Pediococcus, E-coli
Slimy Leuconostoc
Vacuum
Packed
Souring
Greening
Lactobacillus, Carnobacterium,
Leuconostoc
Poultry Odor, Slime
Pseudomonas, Alcaligenes, Xanthomonas

35.  Enterotoxin.
 Contamination occurs usually via improper slaughter procedures
or improper and unsanitary handling of cooked product.
 Produces a potent toxin that cause sever damage to the lining of
the intestine .
 E. coli is one of the most wide spread organisms in nature.
ESCHERICHIA COLI (INTOXICATION)
ASSOCIATEDFOODS
 Raw meat
 Cured meats
 Fermented raw meat sausages
 Raw and cooked poultry and fish

37. Severe cramping, watery diarrhea which becomes
grossly bloody occasionally vomiting, low grade fever
lasts up to 8 days.
E.Coli 0157: H7 - Hemolytic uremic syndrome – renal
failure.
As few as 10 organisms are sufficient to cause the
disease.
Associated with undercooked hamburger, dry-cured
salami, raw meat, smoked meat.
Mortality rate in elderly as high as 50%.
SYMPTOMS

38. E-COLI GROWTH ON MEDIA
E-Coli streaked
and grown on
nutrient agar.
E-Coli streaked
and grown on
EMB agar.

39. MICROBIOLOGICAL
SAMPLING
AND
TESTING

40. — The purpose of microbiological testing is to determine the degree
of bacterial contamination on surfaces of equipment, tools,
premises as well as in meat and meat products.
— Qualitatively testing can be done by determining the exact
number of microorganism per sample unit (in cm2 or grams) by
using the swab.
— Quantitatively testing can be either determination of the entire
contaminating flora, also called “total plate count” or
determination of a specific group of microorganisms out of the
entire flora, also called “selective plate count”.
THE PURPOSE

41. AEROBIC PLATE COUNT
ENVIRONMENTAL SWABS
Interpretation
CFU Count Per
Area Swabbed
Log
Conversion
Counts on
Surface* (based
on 25 cm2
surface area
sampled)
Clean < 45 CFU < 1.65 < 5 CFU / cm2
Contaminated 140 to 260 CFU 2.15 – 2.41 ~ 5 to 10 CFU / cm2
Very Contaminated > 260 CFU > 2.41 > 10 CFU / cm2

42. CARCASS TESTING
 Pathogenic bacteria transferred to carcasses are usually
present in small numbers and on a small area of the carcass.
 Hence negative result for pathogenic bacteria will not
guarantee their absence.
 Large surface area of a high proportion of carcasses needs to
be tested to obtain a statistically valid result for many
pathogenic bacteria.
 This is not economically feasible. However control is achieved
by setting E.coli as an indicator.

43. Qualitative Method for Microbiological testing
of Meat/ Meat Products
4. Homogenizing meat
sample (in “Stomacher”)
3. Trimming/weighing of
meat sample
2. Cutting out meat
sample from carcass
1. Determination of
standardized sample
Bacterial collection by
swab
Inoculation of swab in
sterile buffer

45. APPLICATION OF PLATE COUNT
•Check quality of Raw materials & final
products.
•Check condition hygiene.
•Estimate storage life of products
•Determine
–Production
–Transport
–Storage
•Determine pathogens.

46. METHODS OF PRESERVATION
 Meat is an ideal medium for microbial growth and hence a highly perishable
commodity.
 Some degree of preservation is needed to prevent spoilage of meat.
 Important means of preservation:
— Chilling
— Freezing
— Cooking (including canning)
— Curing (often with smoking)
— Drying
 No appreciable change in property in low temperature preservation.
 Other methods yield a product that is clearly different from fresh meat.

47. CONTROL
 Care should be taken to see that contamination from
different sources should be at the minimum.
 The concept of hazard analysis critical control point
(HACCP) should be in place in meat processing units.
 Irradiation can be done which is FDA approved.
 Cook to internal temperature of 144OF (62O C). Margin of
safety is 160 OF (72O C).
 Curing such as for ham and some sausages.

48. “Let Food be thy medicine
And
Medicine by thy food.”
Hippocrates, 460 B.C.