Putrefactionof Food

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

Putrefaction of different food products

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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