Putrefaction is the anaerobic breakdown of proteins by microorganisms, producing foul-smelling compounds such as hydrogen sulfide and amines. It occurs when protein foods are broken down by proteolytic microorganisms into amino acids, ammonia, and hydrogen sulfide. Factors that affect putrefaction include the chemical composition and structure of food, temperature, pH, and the types of microorganisms present. Putrefaction can change the nutritional value, organoleptic properties, and safety of foods. Various foods are susceptible to putrefaction by different microorganisms if temperature abuse or lack of preservation methods allows the microbes to grow.
2. Putrefaction is anaerobic breakdown of proteins, with the
production of foul-smelling compounds such as hydrogen sulfide
and amines.
Formula of putrefaction:
Protein foods + proteolytic microorganisms
Amino acids + ammonia + hydrogen sulphide
3. Why putrefaction occur
• Nitrogen in food is in form of proteins
• Enzymes of microorganism hydrolyzed protein into
polypeptide, simpler peptides or amino acid before they
can serve as nitrogenous food for most organisms
• This gives flavors desirable or undesirable to some food
• Foul smelling in result of putrefaction is due to sulfur
containing products, such as hydrogen, methyl, and ethyl
sulfides and mercaptans, also ammonia, amines(e.g.
histamine, tyramine, piperidine, putrescine, and
cadaverine), indole, skatole, and fatty acids
4. Effect of putrefaction:
Changes in nutritional value
Decomposition of protein
Change in organoleptic features
Colour, flavour, taste, odour, mucilaginous
surface
Unwholesome effects
Biogenic amines
toxins
5. Source of microbial spoilage
Ubiquiter microorganisms
From natural sources like soil, water, air.
Special source of contamination
Spoiled raw materials
Biofilm on surface of equipment
Human’s personal hygiene
8. Milk
The hydrolysis of milk protein by microorganisms usually
accompanied by the production of a bitter flavor caused by some of
the peptides released.
Types of change produced by proteolytic microorganism:
Acid proteolysis: acid production and proteolysis occur together
Proteolysis with little acid or even alkalinity
Sweet curdling, caused by rennin like enzymes of the bacteria at early
stage of proteolysis
Slow proteolysis by intracellular enzyme of bacteria after autolysis
Residual proteolytic activity of heat stable proteinases
e.g. Pseudomonas fluorescens produces a proteinase that will survive
pasteurization even though the bacteria does not.
9. Acid proteolysis causes the production of shrunken curd and
the expression of much whey
It is done by slow digestion of the curd, appear changes from
opaqueness to translucency and may be by completely
dissolved by some kind of bacteria.
Acid proteolysis is mainly caused by species of Micrococcus
Streptococcus faecalis var. liquefaciens, causes proteolysis in
pasteurized milk
Spore of lactose fermenting, bacillus species can survive
pasteurization or a more rigorous heat treatment of milk and
cause acid proteolysis
10. Active proteolytic bacteria in milk
Micrococcus
Alcaligens
Pseudomonas
Proteus
Flavobacterium
Serratia
Spoilage condition in milk:
Higher pasteurization temperatures
Psychrotrophic capacity of some bacilli
Longer holding or shelfing times
11. Preservation techniques
Pasteurization: mild heat treatment
To kill all the pathogens that may entered milk and be transmitted to people
To improve the keeping quality of milk
classis method of pasteurization: heating upto 60°C for at least 20 min
High temperature short time: temperature of at least 72°C for at least 15min
Ultra high temperature: temperature above 135°C for at least 2 sec
Refrigerated storage
The grade A raw milk for pasteurization: cooled to 10°C or less within 2 hrs
Newly pasteurized milk is to be cooled to 7.2°C or less
12. Eggs
To cause spoilage of an undamaged shell the casual
microorganism must do the following:
i. Contaminate the shell
ii. Penetrate the pores of shell to shell membranes
iii. Grow through shell membrane to reach the white
iv. Grow in egg white and then to reach egg yolk where they can
grow readily and complete spoilage of egg
Time required for bacteria to penetrate the shell
membranes varies with organisms and temperature.
13. Spoilage of eggs
Major rots of eggs
Black rots:
Eggs are almost opaque to the candling lamp
Egg white is in Muddy brown in color
Odor is putrid, with hydrogen sulfide evident and gas pressure
Caused by species of Proteus, species of pseudomonas and
Aeromonas
Proteus melanovogenes causes black color in yolk and dark color in
white
Black rot in egg means that the egg has at some time been held at
temperature higher than those ordinarily used for storage
14. Preservation technique
Removal of dirt, bloom and part of microorganisms by washing with warm
and plain water
Use of heat:
The maximal time at different temperatures for heating in water in order to
avoid coagulation, e.g. 800 sec at 57.5°C
A thermostabilization
use of low temperatures:
Chilling: cooling of egg as practicable after production and held at a
temperature and relative humidity
Use of preservatives: used on the shell of eggs
To keep shell dry and reduce penetration of oxygen into eggs
E.g. sodium silicate for home method preservation
15. Meat and meat products
The preliminary hydrolysis of proteins by meat
enzymes helps microorganisms start growing in the
meat by furnishing the simple nitrogen compounds
needed by many microorganism that cannot attack
complete native protein.
The microorganisms come chiefly from the exterior
of the animal and its intestinal tract but the more are
added from general things like knives, clothes, air,
workers, carts, boxes and equipment.
16. Growth of microorganisms in meat
Meat is an ideal culture medium for many organisms because it is
high in moisture, rich in nitrogenous foods of various degrees of
complexometry, have favorable pH for most microorganisms.
Factors influencing the growth of microorganisms:
The Kind and amount of microorganisms
Chemical properties like moisture content at surface, low carbohydrate
but high protein content tend to favor the nonfermenting types of
organisms, pH of raw meat.
Temperature
17. Spoilage under anaerobic condition
facultative and anaerobic bacteria are able to growth within
the meat under anaerobic conditions and cause spoilage.
Putrefaction:
Caused by species of clostridium, but facultative bacteria may cause
putrefaction or assist in its production
Other species like:
putrefaciens
putrificum
putida
Chiefly the genera Pseudomonas and Alcaligenes
Some species of Proteus
18. Spoilage of different kind of meats
Hamburger
At room temperature usually putrefies, but at temperatures near freezing
acquires a stale, sour odor, and at higher temperature a large number of
kinds of microorganisms have been found
Among the genera reported are Bacillus, Clostridium, Escherichia,
Enterobacter, Proteus, Pseudomonas, Alcaligenes, Lactobacillus,
Leuconostoc, streptococcus, Micrococcus, and Sarcina of the bacteria,
and Penicillium and Mucor of the molds
19. Ham
The term souring as used for the spoilage of hams, covers all important
types of spoilage, from a comparatively nonodorous proteolysis to
genuine putrefaction with its very obnoxious odors
species for spoilage: Alcaligenes, Bacillus, Pseudomonas, Lactobacillus,
Proteus, Serratia, Micrococcus, Clostridium and hydrogen sulfide
producing Streptobacilli that causes flash souring of hams
when the long cure was used on hams, putrefaction by Clostridium
putrefaciens was more common
Curing solutions or pickles
Spoilage of multiuse brines usually is putrefactive and is caused by
Vibrio, Alcaligenes, or Spirillum
black spots on pickled pigs feet caused by hydrogen sulfide producing
bacteria
20. Preservation technique
Use of heat:
Canning of meat
Chemicals such as spices, salt or nitrates and nitrites in meat curing process
Commercially canned meats can be divided into two group
I. Meats that are heat processed in attempt to make the can contents
sterile
II. Meats heated that can kill part of spoilage organisms but must be kept
refrigerated to prevent spoilage
Use of low temperature:
Chilling: temperatures near freezing and chilling storage at slightly above
the freezing point. Less opportunity of growing of mesophilic
microorganisms.
Freezing: used to preserve meet during shipment to other places
21. Preservation technique
Drying: in dried beef, smoked beef hams
Meat products like dry sausages, dry salamis are preserved chiefly by
their low moisture content
Drying pork involves a short nitrate-nitrate cure before drying and
addition of lecithin as an antioxidant and stabilizer
Freeze drying of meats
Curing: products like hams, beef, pork, butts
Sodium chloride, sugar, sodium nitrate and vinegar are permitted curing
agents
22. Spoilage of fish
The flora of living fish depends upon the microbial content of the
waters in which they live.
The slime that covers the outer surface of fish has been found to
contain bacteria of genera Pseudomonas, Alcaligenes, Micrococcus,
Flavobacterium, Corynebacterium, Sarcina, Serratia, Vibrio, Bacillus
Fish have a high content of nonprotein nitrogen and autolytic changes
caused by their enzymes increase the supply of nitrogenous foods and
glucose for bacterial growth. From these compound the bacteria make
trimethylamine, ammonia, amines, lower fatty acids and hydrogen and
other sulfides
Streptomyces species causes musty or muddy odor and taste of fish
23. Preservation technique
Use of low temperatures: only after death of fish that autolysis
gets under way, with softening and production of off flavor and
microbial growth becomes uncontrolled; these changes are
delayed by rigor mortis
Chilling: to preserve fish during shipment
24. Spoilage of canned foods
Bacterial spoilage of canned foods by microorganisms may result
from
Survival of organisms after heat treatment
Leakage of the container after heat treatment
Types of biological spoilage caused by microorganism divided
into
Caused by thermophilic bacteria
Caused by mesophilic microorganisms
25. Spoilage by thermophilic bacteria
Sulfide, or “sulfur stinker,” spoilage
Mainly caused by Clostridium nigrificans found in low acid food like
corn and peas
Hydrogen sulfide, formed in the canned corn is evident by odor when
the can is opened
In corn, a bluish green is evident in which blackened germs and gray
kernels of corn float
Peas give the hydrogen sulfide odor but without any marked
discoloration
26. Spoilage by Mesophilic Clostridium Species
Species like C.sporogenes, C.Putrefaciens and C.botulinum, are
putrefactive , decomposing protein with the malodorous compounds
The spore of the putrefactive anaerobes are very heat resistant
The putrefactive anaerobes grow best in the low acid canned foods
but may spoil medium acid foods
One of the putrefiers, C. botulinum, is a cause of food spoilage
C.sporogenes produces gases in canned meats and fish