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
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
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
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
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
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.
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
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
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
Eggs To cause spoilage of an undamaged shell the casual
microorganism must do the following:i. Contaminate the shellii. Penetrate the pores of shell to shell membranesiii. Grow through shell membrane to reach the whiteiv. 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.
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
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
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.
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
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
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
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
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
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
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
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
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
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
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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