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.

1. Putrefaction
of Food

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

6. Factors affecting microbial spoilage
 Intrinsic factors of foodstuffs
 Water activity, pH
 Chemical composition: nutrient, minerals, vitamins, inhibitors
 Biological structure
 Extrinsic factors of foodstuffs
 Temperature, humidity, atmosphere composition
 Processing effects
 Hygiene, cleaning, disinfections
 Implicit parameters
 Interaction of microorganisms
 Reproductive potential

7. Putrefaction of different
food products

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

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