Meat is highly perishable due to microbial spoilage if not properly preserved. The main causes of meat spoilage are microbial contamination during the slaughtering and processing of animals, as well as lipid oxidation and autolytic enzymatic breakdown during storage. Under aerobic conditions, spoilage occurs via surface slime, molds, discoloration and off odors produced by bacteria. Under anaerobic conditions, spoilage involves souring, putrefaction and bone taint caused by bacteria such as Clostridium producing acids, gases and foul compounds. Proper handling and storage are necessary to limit microbial growth and chemical breakdown that reduce meat quality and shelf life.

1. Spoilage of meat and
meat products
Darshan

2. Contents
• Introduction
• Causes of meat spoilage
• Mechanism of spoilage
• Conclusion
• Reference

3. Introduction
● Nutritious, protein-rich food which is highly perishable and has a short shelf-life
unless preservation methods are used
● First-choice source of animal protein for many people all over the world
● Despite its usage and demand for it, every year significant portion of meat and
meat products are spoiled
● Significant portion of this loss is due to microbial spoilage (other reasons for
spoilage of meat and meat products include lipid oxidation and autolytic enzymatic
spoilage)

4. The transformation of animals into meat involves several
operations
● Handling and loading of animals on the farm
● Transporting animals to slaughterhouses
● Off-loading and holding of animals
● Slaughtering of animals (involves stunning, bleeding, skinning,
evisceration and carcass splitting)
Poor operational techniques and facilities in any of these operations will
result in unnecessary suffering and injuries to animals which can lead to
reduced meat quality and spoilage of meat

5. ● Fat, protein, minerals,
carbohydrate and water
are the constituents of
meat
● Lipid oxidation, protein
degradation and the loss
of other valuable
molecules are the
consequence of meat
spoilage process
● Proteins and lipids can
break down resulting in
the production of new
compounds causing
changes in meat
Product Water (%) Protein (%) Fat(%) Energy (cal/100g)
Beef (lean) 75.0 22.3 1.80 116
Beef carcass 54.7 16.50 280.00 323
Pork (lean) 75.1 22.8 1.2 469
Pork carcass 47.1 11.2 47.0 1975
Veal (lean) 76.4 21.3 0.8 410
Chicken 75.0 22.8 0.9 439
Composition of meat
*Heins and Hautzinger, 2007

6. Causes of meat spoilage
● Preslaughter handling of livestock and postslaughter handling
of meat play an important part in deterioration of meat quality
● The glycogen content of animal muscles is reduced when the
animal is exposed to pre-slaughter stress which changes the pH
of the meat
● Lactic acid is produced due to the breakdown of glycogen
content of animal muscles via an anaerobic glycolytic pathway

8. • Higher levels of pH (6.4-6.8)
result in Dark, Firm and Dry (DFD)
meat. Long term stress causes
DFD meat which has a shorter
shelf life
• Severe short term stress results
in a Pale, Soft and Exudative (PSE)
meat
• PSE meat has a pH lower than
normal ultimate value of 6.2
which is responsible for the
breakdown of proteins, providing
a favourable medium for the
growth of bacteria
Normal meat
PSE meat
DFD meat

9. Oxidation of lipids
● Responsible for both desirable and undesirable flavours and
aromas in meat
● Autoxidation of lipids is natural processes which affect fatty
acids and lead to oxidative deterioration of meat and off-
flavours development
● After slaughtering of animals, the fatty acids in tissues
undergo oxidation when the blood circulation stops and
metabolic processes are blocked

10. Autolytic spoilage
● Enzymatic actions are natural process in the muscle cells of the animals
after they have been slaughtered and are the leading cause of meat
deterioration
● Complex compounds (carbohydrates, fats and protein) of the tissues are
broken down into simpler ones resulting in softening and greenish
discoloration of the meat
● Proteolysis and fat hydrolysis: prerequisite for microbial decomposition
● Excessive autolysis is termed souring

11. Microbial spoilage
● Growth media for a variety of micro flora (bacteria, yeasts and molds)
● Intestinal tract, skin of the animal and other extrinsic factors are the main
sources of these microorganisms
● Properties of meat influencing microbial growth
● Physical properties of meat: surface area of meat is proportional to growth of
microorganisms
● Nutrient composition
● Availability of oxygen
● Water activity
● Temperature

12. Genus Gram reaction Fresh meats Fresh livers Poultry
Acinetobacter - XX X XX
Bacillus + X X
Citrobacter - X X
Clostridium + X X
Enterococcus + XX X X
Escherichia - X X
Flavobacterium - X X X
Lactobacillus + X
Listeria + X XX
Microbacterium + X X
Proteus - X XX
Pseudomonas - XX XX
Salmonella - X X
Staphylococcus + X X X
* Jay et al, 2005

13. * Jay et al, 2005
Genus Fresh and refrigerated meats Poultry
Molds
Alternaria X X
Aspergillus X X
Cladosporium XX X
Fusarium X
Mucor XX X
Neurospora X
Penicillium X X
Rhizopus XX X
Sporotrichum XX
Thamnidium XX
Yeasts
Candida XX XX
Rhodotorula X XX
Saccharomyces X

14. Source(s) of microflora:
● Gut flora
● Physiological conditions before slaughtering
● Method of cleaning and bleeding
● Storage conditions

15. Mechanism of spoilage
● Consumption of utilizable substrate or production of new product(s) by
spoilage microbiota
● Low temperature spoilage is accompanied by the production of off-color
compounds such as ammonia, H2S, indole, and amines
● Among the metabolic byproducts of meat spoilage, the diamines, cadaverine,
and putrescine, have been studied as spoilage indicators of meats

16. Spoilage under aerobic
conditions

17. Aerobic growth of moulds may cause the
following:
● Stickiness: Incipient growth of moulds
makes the surface sticky
● Whiskers: Thamnidium, Mucor and
Rhizopus cause whiskers on beef. When
meat is stored at temperatures near
freezing, a limited amount of mycelial
growth may take place without
sporulation.
● Black spot- Cladosporium herbarum and
white spot- Sporotrichum carnis moulds
like Geotrichum.
● Green patches-Penicillium expansum,
Penicillium asperulum, and Penicillium
oxalicum.

18. Surface slime
● Caused by species of Pseudomonas, Acinetobacter,
Alcaligens, Micrococcus, Streptococcus,
Leuconostoc, and Bacillus
● The spoilage microflora forms a thin film on meat, which
enables them to obtain nourishment from the substrate

19. Changes in colour of meat pigments
● The red colour of meat, called its “bloom,” may be changed
to shades of green, brown, or grey
● It is due to the production of oxidizing compounds like
peroxides, or hydrogen sulfide, by bacteria
● Species of Lactobacillus (mostly heterofermentative)
and Leuconostoc are reported to cause the greening of
sausage

20. • Changes in fats : Lipolytic bacteria
like Pseudomonas and Achromobacter and yeasts may cause some lipolysis
and also accelerate the oxidation of the fats
• Phosphorescence: Uncommon defect caused by
phosphorescent or luminous bacteria. Eg
Photobacterium spp.
• Surface discoloration : The “red spot” may be
caused by Serratia marcescent. Pseudomonas
syncyanea can impart a blue colour to the
surface. Yellow discolorations are caused by
species of Micrococcus or Flavobacterium,
Chromobacterium lividum

21. Off odours and off tastes
● Taints and souring or undesirable odours and tastes in meat
are the result of the growth of bacteria on the surface
● This' maybe due to production of volatile acids such as
formic, acetic, butyric and propionic acids. Or maybe due to
musty or earthy flavour due to actinomycetes

22. Spoilage under anaerobic
conditions

23. Souring
● The term implies a sour odour and perhaps taste.
● Could be caused by formic, acetic, butyric, propionic, and
higher fatty acids or other organic acids such as lactic or
succinic acid
● There is gas formation accompanying the action of the
“butyric” Clostridium species and the coliform bacteria on
carbohydrates

24. Putrefaction
● True putrefaction is the anaerobic decomposition of protein
with the production of foul-smelling compounds such as
hydrogen sulfide, mercaptans, indole, skatole, ammonia, and
amines
● It is usually caused by species of Clostridium, but can also
by Pseudomonas, Proteus, and Alcaligenes

25. Bone taint
● Refers to souring or putrefaction of meat next to bones

26. Conclusion
● Fat, protein, minerals, carbohydrate and water are constituents of
meat
● Lipid oxidation, protein degradation and loss of other valuable
molecules are the consequence of meat spoilage process
● Change in glycogen content confers pH change in meat
● Meat spoilage is brought by microbial spoilage, lipid oxidation or
autolytic enzymatic spoilage
● Availability of oxygen along with various other factors and type of
spoilage microorganism confer type of spoilage

27. Reference
● R. A. Lawrie, D. A. Ledward 2006, Lawrie’s meat science, woodhead
publishing limited
● D. Dave and A. E. Ghaly 2011, Meat spoilage mechanisms and
preservation techniques: A critical review

28. Thank You!