This document summarizes types of meat spoilage caused by microorganisms. It discusses how meat becomes contaminated during slaughter and processing, allowing microbes like bacteria, yeasts and molds to grow. The major types of spoilage include: 1. Aerobic bacteria can cause surface slime, discoloration, gas production, odor changes and fat decomposition. Pseudomonas is a common genus. 2. Anaerobic bacteria may cause souring through acid production or putrefaction characterized by foul odors. Clostridium bacteria are major putrefiers. 3. Temperature influences spoilage microbes, with refrigeration permitting growth of psychrotrophs like Pseudomonas, Lact

1. Presented By: GEETARANI LOUSHIGAM
Of MSc Food Technology and Quality Assurance, 2020-22
COLLEGE OF INDIGENEOUS FOOD TECHNOLOGY, KONNI
FOOD MICROBIOLOGY
Spoilage of meat

2. CONTENTS
Meat
1
Contamination
2
Spoilage
3
General types of spoilage in meat
4
Spoilage of different kinds of meat
5

3. MEAT
 Meat refers to the muscles of warm-blooded terrestri
al four-legged animals, the chief ones being cattle,
sheep and pigs.
 Meat also includes the glands and organs of these
animals.
 Meat products include many of the byproducts from
animal slaughter, such as animal gut used for sausage
casings, the fat from the meat used in the manufacture
of lard, gelatin and others.

4. CONTAMINATION
 Food contamination is when food is contaminated with microbes and any other substance and eating it could result
in foodborne illness.
 The healthy inner flesh of meats have been reported to contain few or no organisms but they have been found in
lymph nodes, bone marrow, & even flesh.
 Staphylococci, Streptococci, Clostridium, & Salmonella have been isolated from the lymph nodes of red meat animals.
Hence, lymph nodes are removed from the edible parts during slaughtering practices
 Approved “humane” methods of slaughter- mechanical, chemical, electrical- have little effect of contamination.
 The important contamination comes from external sources during bleeding, handling & processing.
 During bleeding, skinning & cutting, the main source of micro-organisms are the exterior of the animal & intestinal
tract

6. Frequently Isolated Microorganisms from Meats
Candida, Torulopsis, Debaryomyces,
and Rhodotorula.
Yeasts
Cladosporium, Geotrichum, Sporotrichum,
Mucor, and Thamnidium.
Molds
Acinetobacter, Moraxella, Pseudomonas,
Aeromonas, Alcaligenes, and Micrococcus
Bacteria
Debaryomyces, Torula, Torulopsis,
Trichosporon, and Candida
.
Yeasts
Aspergillus, Penicillium, Rhizopus, and
Thamnidium
Molds
Lactobacillus and other lactic acid
bacteria, Acinetobacter, Bacillus, Micro
coccus, Serratia, and Staphylococcus
Bacteria
Fresh and Refrigerated Meat Processed and Cured Meats

7. SPOILAGE
Food spoilage is any undesired change in the natural color, taste or texture of food items that makes
it unfit for consumption as it has lost its quality and nutritional value.
Raw meat is subjected to change by its own enzymes & by microbial action & its fat may be oxidized
chemically.
Factors that influence the microbial invasion include:-
a. The load of gut of the animal- more the load, greater the invasion of tissues.
b. The physiological condition of the animal immediately before slaughter- if the animal is excited,
feverish bacteria is more likely to be enter the tissues.
c. The method of killing & bleeding- the better sanitary the bleeding, better would be the keeping
quality of meat.
d. The rate of cooling- rapid cooling will reduce the rate of invasion of tissues

8. Factors that influence the growth of microorganisms to cause spoilage
1. The kind and amount of contamination with microorganisms & the spread of these organisms in
the meat.
2. The physical properties of meat-
The amount of exposed surface of the flesh influence on the rate of spoilage.
3. The chemical properties of meat-
The moisture content of the meat determine organisms to grow.
4. Availability of oxygen-
Aerobic conditions at the surface of meat are favorable to yeasts, molds & aerobic bacteria.
5. Temperature-
Low-temperature organisms can grow on stored temperature of meat i.e. not far above freezing.

9. GENERAL TYPES OF SPOILAGE OF MEAT
Aerobic Bacteria
 Surface slime
 Discolorations
 Gas production
 Change in odors
 Fat decomposition
Anaerobic Bacteria
 Souring
 Putrefaction
and foul odor
 Taints
Mold
 Sticky and
whiskery surface
 Discolorations
 Changes in odor
 Fat decomposition
Yeast
 Surface slime
 Discolorations
 Changes in odor
and taste
 Fat decomposition

10. Aerobic bacteria
1. Surface slime-
 which may be caused by species Pseudomonas, Leuconostoc, Bacillus, Alkaligenes,
Micrococcus etc.
 Temperature & availability of moisture, influence the kind of organisms causing surface
slime.
2. Changes in color of meat pigments-
 The production of oxidizing agents causes change in red color of meat to shades of green,
brown & gray, by bacteria species of Lactobacillus.
 Red color of meat called as “bloom”.
 Species of Lactobacillus and Leuconostoc causes greening of sausages.
3. Changes in fats-
 The oxidation of unsaturated fats in meats takes place chemically in air & may be catalyzed
by light & copper.
 Lipolytic bacteria may cause lipolysis off flavor due to aldehyde & acids.
 Lipolytic species viz., Pseudomonas & Achromobacter.

11. 4. Phosphorescence-
 Uncommon defect caused by luminous bacteria.
 Ex. Photobacterium growing on the surface of meat.
5. Various surface color due to pigmented bacteria-
 Red spot caused by Serratia marcescens.
 Blue colour caused by Pseudomonas syncyanea.
 Yellow pigments produced by the sps of Micrococcus or Flavobacterium.
 Greenish blue to brownish black spots on stored beef caused by Chromobacterium lividum.
 Purple “stamping ink” discoloration of surface fat caused by yellow pigmented cocci and rods.
6. Off odors and off tastes-
 “Taints” or undesirable tastes & odors, appear in meat due to growth of bacteria on the surface often
are evident before other signs of spoilage.
 Souring is term applied to almost any defect, that gives a sour odor may be due to volatile acid.
 “Cold storage flavor” or taint is an indefinite term for a stale flavour.
 Actinomycetes may cause musty or earthy flavour.
Contd..

12. Aerobic growth of yeast
 Surface slime
 Discolorations
 Change in odor and taste
 Fat decomposition

13. Aerobic growth of molds
 Stickiness: Incipient growth of molds makes the surface of the meat sticky to the touch.
 Whiskers: White fuzzy growth can be caused by a number of molds including sps. Thamnidium,
Mucor, Rhizopus and others.
 Black spot: Cladosporium herbarum.
 White spot: Sporotrichum carnis, Geotrichum.
 Green patches: Penicillium expansum, Penicillium asperulum, Penicillium oxalicum.
 Decomposition of Fats: Many molds have lipases and hence cause hydrolysis of fats.
 Off odour and off tastes: Molds give a musty flavour to meat in the vicinity of their growth.
Sometimes this defect is given a name called “thamnidium taint”.

14. Whisker meat Green patches in meat Black spot in meat

15. ANAEROBIC bacteria
Facultative and anaerobic bacteria are able to grow within the meat under anaerobic conditions to cause
spoilage. The terminology used in connection with this spoilage is:-
1. Souring:-
 The term implies a sour odor.
 This could be caused by formic, acetic, butyric, propionic and higher fatty acids or other organic
acid like lactic.
 Vacuum packed meats, especially those in gastight wrappers, commonly support the growth of lactic
acid bacteria.
 Acid and gas formation accompany the action of the “butyric” Clostridium spps and the coliform
bacteria on carbohydrates.
Souring can result from-
 Action of meat own enzymes during ripening
 Anaerobic production of fatty acids or lactic acid during ripening.
 Proteolysis without putrefaction, caused by anaerobes & called as “Stinking sour fermentation”.

16. 2. Putrefaction:-
 True putrefaction is the anaerobic decomposition of protein with the production of foul smelling
compounds.
 It usually is caused by species of Clostridium.
 But facultative bacteria may cause putrefaction in its production, by species of Pseudomonas
like P. putrefaciens, P. putrificum etc, chiefly in the genera Pseudomonas and Alcaligenes.
 Gas formation accompanies putrefaction by clostridia, the gases being hydrogen & CO2.
 Trimethyl amine in fish and isovalenic acid in butter are described as putrid odors.
3. Taint:-
 This word is implied to any off-taste, off-odor.
 The term ‘bone taint’ is implied to souring or putrefaction.
 True putrefiers require temperature above those of refrigerator.
Contd..

17. SPOILAGE IN DIFFERENT KINDS OF MEATS
 Extended refrigeration may have the growth of Pseudomonas, Acinetobacter, Moraxella and causes
spoilage of fresh meat
 Lactic acid bacteria chiefly of the genera Lactobacillus, Leuconostoc, Streptococcus, Brevibacterium and
Pediococcus are present in most meats, fresh or cured and can grow even at refrigerator temperatures.
1. Spoilage of Fresh meats:
 Putrefaction, Souring, Phosphorescence, discolorations. (Pseudomonas & Micrococci).
2. Fresh beef:
 Bacillus, Clostridium, Escherichia coli, Enterobacter, Proteus, Pseudomonas, Alcaligenes, Lactobacillus,
Leuconostoc, Streptococcus, Micrococcus and Sarcina.
3. Hamburger:
 Lactobacilli, Leuconostocs, Microbacterium, Micrococcus, Alternaria.
4. Fresh pork sausage:

18. SPOILAGE OF DIFFERENT KINDS OF MEATS
 Sodium nitrite lactic acid bacteria in sausages like thuringer & leads to lactic acid fermentation
5. Spoilage of cured meats:
 Sour – by variety of bacteria
 Red – due to Halobacterium salinarum or red Bacillus sps.
 Blue – Pseudomonas syncyanea, Penicillum Spinulosum (purplish), Rhodotonela sps.
6. Dried Beef or Beef Hams:
 Aspergillus, Alternaria, Monilia, Oidium, Fusarium, Mucor, Rhizopus, Botrytis and Penicillium.
7. Bacon:
 Greening of sausage is due to the production of peroxides (Ex: H2O2) by hetero-fermentative sps of Lactobacillus and
Leuconostoc or other catalase negative bacteria.
 Acid forming Micrococci (Micrococcus candidus) and Bacillus may grow in liver sausage and bologna.
8. Sausages:

19. SPOILAGE OF DIFFERENT KINDS OF MEATS
 Souring caused by Alcaligenes, Bacillus, Pseudomonas, Lactobacillus, Proteus, Serratia, Bacterium,
Micrococcus, Clostridum.
9. Ham:
 Pseudomonas, Acinetobacter and Moraxella
10. Refrigerated packaged meats:
 Multiuse brines generally spoiled by putrefactive bacteria.
Ex: Vibrio, Alcaligenes or Spirillum.
 Souring can be caused by Lactobacillus and Micrococcus and slime by Leuconostoc or Micrococcus lipolytics.
11. Curing solutions (or) pickles:

20. SPOILAGE IS ALSO INFLUENCED BY TEMPERATURE
Not only air but temperature has an important influence on the type of spoilage to be expected in meat.
When meat is held at temp. near 0°C, microbial growth is limited to molds, yeasts, & bacteria able to grow
at low temperatures.
This include:- sliminess, discoloration and spots of growth on the surface.
Many bacteria can cause souring. Such as Pseudomonas, Lactobacillus, Leuconostoc, Streptococcus.. etc.

21. Thank you