c. Spoilage of i. Meat and Poultry products ii. Bread iii. Fruits and Vegetables iv. Eggs v. Sea foods vi. Canned foods

c. Spoilage of

i. Meat and Poultry products

ii. Bread

iii. Fruits and Vegetables

iv. Eggs

v. Sea foods

vi. Canned foods

i. Meat and Poultry products

Spoilage of meat and meat products:

Raw meat is subject to change by it's own enzymes and by microbial action, and it's fat may be oxidized chemically.
A moderate amount of autolysis is desired in the tenderizing of beef and game by hanging, or aging, but is not encouraged in most other raw meats.
Autolytic changes include some proteolytic action on muscle and connective tissues and slightly hydrolysis of fats.
The defect caused by excessive autolysis has been called " souring" an inexact term that is applied to a variety of kinds of spoilage of food and to in fact almost any kind that gives a sour odor.
Souring due to autolysis is difficult to separate or distinguish from defects caused by microbial action, especially from simple proteolysis .

General Principles underlying meat spoilage:
It has been pointed out that during slaughter, dressing and cutting, microorganisms come chiefly from the exterior of the animal and its intestinal tract but that more are added from knives, cloths, air, workers, carts, boxes, and equipment in general .
A great variety of kinds of organisms are present and will be able to grow if favorable conditions present themselves.

Invasion of Tissues by Microorganisms:
Upon the death of the animal, invasion of the tissues by contaminating microorganisms takes place.
Factor's that influence the invasion include the following-
1.The load in the gut of the animal: The greater the load, the great the invasion of tissues. For that reason starvation for 24hr before slaughter has been recommended.
2. The physiological condition of the animal immediately before slaughter- If the animal is excited, feverish or fatigued, bacteria are more likely to enter the tissues, bleeding is apt to be incomplete, thus encouraging the spread of bacteria, and chemical changes may take place more readily in the tissues, such as those due to better bacterial growth because of a higher pH, earlier release of juices from the meat fibers  and more rapid denaturation of proteins.
3. The method of killing and bleeding- The better and more sanitary the bleeding, the better the keeping quality of the meat.Little has been reported on the effect of humane methods of slaughter on the keeping quality of meat, although it has been claimed that more greening was found in pork and bacon from electrically stunned animals than from those killed with carbon dioxide.
4.The rate of cooling- Rapid cooling will reduce the rate of invasion of the tissues by microorganisms.

Microorganisms are spread in the meat through the blood and lymph vessels and connective-tissue interspace, and in ground meat by grinding.

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 complexity, and plentifully supplied with minerals and accessory growth factors.
The factors that influence the growth of Microorganisms  are as fallows :
1.The kind and amount of contamination with microorganisms and the spread of these organisms in the meat- For example , meat with a contaminating  flora  that is high in percentage of psychotrophs  would spoil at chilling temperature more rapidly than meat with a low percentage of these psychotropic organisms.
2. The physical properties of the meat- The amount of exposed surface of the flesh has considerable influence on the rate of spoilage because the greatest load of organisms usually is there and air is available for aerobic organisms.
3. Chemical properties of the meat- It has been pointed out that meat in general is a fine culture medium for microorganisms.  The  moisture content is important in determining whether organisms can grow and what kind can grow, especially  at the surface , where drying may take place.Thus the surface may be so dry as to permit no growth, a little moist to allow mold growth, still moister to encourage yeasts, and very moist to favor bacterial growth.The relative humidity of the  storage atmosphere  is important in this regard.
4. Availability of oxygen- Aerobic conditions at the surface of meat are favorable to molds, yeasts and aerobic bacteria.
5. Temperature- Meat should be stored at temperature not far above freezing ,where only low- temperature microorganisms can grow. Molds, yeasts and psychotropic bacteria grow slowly and produce characteristics defeats.

General Types of spoilage of meats:
The common types of spoilage of meats can be classified on the basic of wheath they occur under aerobic or anaerobic conditions and whether they are caused by bacteria, yeasts, or molds.

A. Spoilage under Aerobic conditions: Under aerobic conditions bacteria may cause the following:

1. Surface slime- which may be caused by species of Pseudomonas , Acinetobacter, Moraxella, Alcaligenes, Streptococcus, Leuconostoc, Bacillus and Micrococcus .
Some species of Lactobacillus can produce slime.
The temperature and the availability of moisture influence the kind of Microorganisms causing  surface slime.
At  chilling temperature, high moisture will favour the Pseudomonas- Alcaligenes group; with less moisture, as on frankfurters, micrococci and yeasts will be encouraged; and with still less moisture, molds may grow.
At higher temperature, up to that of the room , micrococci and other mesophiles  compete well with the pseudomonads and related bacteria.
2.Changes in color of meat pigment - The red color of meat, called its " bloom", may be changed to shades of green, brown, or gray as a result of the production of oxidizing compound, e.g.peroxides, or of hydrogen sulfide, by bacteria.
Species of Lactobacillus ( mostly hetero fermentative) and Leuconostoc are reported to cause the greening of sausage.
3.Changes in fats -  The oxidation of unsaturated fats in meats takes place chemically in air and may be catalyzed by light and copper.
Lipolytic bacteria may cause some lipolysis and also may accelerate the oxidation of the fats.
4. Phosphorescence- This rather uncommon defect is caused by phosphorescent or luminous bacteria, e.g. Photobacterium spp, growing on the surface of meat.
5. Various surface colors due to pigmented bacteria - Thus " red spot" may be caused by Serratia marcescens  or other bacteria with red pigment.
Pseudomonas synçyanea  can impart a blue color to the surface.
Yellow discoloration are caused by bacteria with yellow pigments, usually species of micrococcus or Flavobacterium .
Chromobacterium lividum and other bacteria give greenish-blue to brownish-black spots on stored beef.
The purple " stamping-ink" discoloration of surface fat is caused by yellow - pigmented cocci and rods.
6.Off-odors and off- tastes - "Taints", or undesirable odours and tastes, that appear in meat as a result of the growth of bacteria on the surface  often are evident before other signs of spoilage.
" Souring" is the term applied to almost any defect that gives a sour odor that may be due to volatile acids, e.g. formic, acetic, butyric,and propionic or even to growth of yeasts.
"Cold-storage flavor" or taint is an indefinite term for a stale flavor .
Actinomycetes may be responsible for a musty or earthy flavor.


B.Spoilage under Anaerobic conditions:

Facultative and anaerobic bacteria are able to grow within the meat under anaerobic conditions and cause spoilage. The terminology used in connection with this spoilage is inexact.
Most used are the words " souring " , "purification", and " taint", but these terms apparently mean different things to different people.
1. Souring -
The term implies a sour odor and perhaps taste.
This could be caused by formic , acetic, butyric, propionic, and higher fatty acids or other organic acids  such as lactic or succinic. Souring can result from (a) action of the meat's own enzymes during aging or ripening, (b) anaerobic production of fatty acids or lactic acid by bacterial action, or (c) proteolysis without purification , caused by facultative or anaerobic bacteria and sometimes called " stinking spur fermentation " .
Acids and gas formation accompany the action of the " butyric " Clostridium species and the coliform bacteria on carbohydrates.
Vaccumpacked  meats, especially those in gastight wrappers, commonly support the growth of lactic acid bacteria.
2. Putrefaction -
True putrefaction is the anaerobic decomposition of protein with the production of foul- smelling compounds such as hydrogen sulfide, mercaptans , indole, skatole, ammonia and amines.
It usually is caused by species of Clostridium, but facultative bacteria  cause putrefaction  or assist in it's production , as evidenced by the long list of species  with the specific names putrefaciens, putrificum , putida etc.chiefly in the genera Pseudomonas and Alcaligenes. Also some species of Proteus are putrefactive.
3. Taint -
" Taint" is a still more inexact word applied to any  off- taste or off- odor . The term " bone taint" of meats refers to either souring or putrefaction next to the bones, especially in hams. Usually it means putrefaction.
Not only air but temperature has an important influence on the types of spoilage  to be expected in meat.
When meat is held at  temperature near 0 C ,as recommended, microbial growth is limited to that of molds, yeasts, and bacteria able to grow at low temperatures.
These include many of the types that produce sliminess, discoloration and spots of growth on the surface and many that can cause souring, such as Pseudomonas, Acinetobacter moraxella, Alcaligenes, Lactobacillus, Leuconostoc, Streptococcus and Flavobacterium spp.

Spoilage of different kinds of meats:
The processing of meat by curing, smoking, drying, or canning usually changes them and their microbial flora  enough to encourage types of spoilage not undergone  by fresh meats.
1.Spoilage of Fresh Meats:
The spoilage of fresh meats has been covered in the preceding  discussion of general types of spoilage.
Normally , upon extended refrigeration, Pseudomonas, Acinetobacter and Moraxella species spoil fresh meats.

2.Spoilage of Dried Beef or Beef Hams:

Bacillus, Halobacterium salinarium, red bacillus spp., Pseudomonas syncyanea .

Reference:

Food Microbiology by Willium C.Frazier, Page no 229-239.

Spoilage of Poultry Products:

Poultry meat consumption is steadily increasing worldwide.

Most of the literature dealing with the microbial contamination of poultry meat is dedicated to detecting the presence of pathogens (mainly Salmonella and Campylobacter) and sometimes to studying their behavior under different decontamination, transformation, or storage conditions.

 Poultry meat contamination by spoilage bacteria has been less studied and is often limited to their enumeration by counting CFUs (colony forming units) on different, more or less specific, media. Challenge tests, based on the inoculation of individual strains or strain cocktails on meat cuts, have been used to investigate the growth ability of bacteria under various treatments.

Pseudomonads, often recorded in poultry meat are mainly represented by the species Pseudomonas fragi, Pseudomonas lundensis, and Pseudomonas fluorescens .

Among Enterobacteriaceae, the main genera are Hafnia (Hafnia alvei, Hafnia paralvei), Serratia (Serratia fonticola, Serratia grimesii, Serratia liquefaciens, Serratia proteamaculans, and Serratia quinivorans), Rahnella, Yersinia, and Buttiauxella . 

Several new Enterococcus or Lactobacillus species such as Enterococcus viikkiensis, Enterococcus saigonensis, and Lactobacillus oligofermentans have also been discovered in poultry meat products.

Brochothrix thermosphacta has also been often recorded in poultry meat.

Enterobacteriaceae and Pseudomonas spp. are considered potential spoilers of poultry meat.

ii. Bread

Microorganism are useful in two chief ways in breadmaking:

1.They may produce gas to leaven , or raise, the dough, giving  the bread the desired loose, porous texture and

2. They may produce desirable flavoring substance. They also function in the conditioning of the dough.

Leaving:

Dought is usually leavened by bread yeasts , which ferment the sugars in the dough and produce mainly carbon dioxide and alcohol.

However, other actively gas-forming microorganism, such as wild yeasts, coliform bacteria, saccharolytic , Clostridium species, heterofermentative lactic acid bacteria, and various naturally occurring mixtures of these organisms, have been used instead of bread yeasts for leaving. Leaving also may be accomplished by the direct incorporation of gas ( carbon dioxde) in the dough.

Some changes caused by microorganisms are desirable and even necessary in making certain kinds of bread.

The acid fermentation by lactic and coliform bacteria that is normal in flour pastes or or doughs may be too extensive if too much time is permitted, with the result that the dough and bread made from it may be too ‘sour’.

Excessive growth of proteolytic bacteria during this period may destroy some of the gas-holding capacity so essential during the rising of the dough and produce a sticky dough.

Sticky doughs, however, are usually the result of overmixing or gluten breakdown by reducing agents, e.g., glutathione.

There also is the possibility of the production by microorganisms of undesirable flavours other than the sourness.

HJistorically, the chief types of microbial spoilage of baked bread have been moldiness and ropiness, usually termed “mold” and “rope”.

Mold:

Molds  are the most common and hence the most important cause of the spoilage of bread and most bakery products.

The temperature attained in the baking procedure usually  are high enough to kill all mold spores in and on the loaf,so that molds must reach the outer surface or penetrate after baking.

They can come from air during cooling or thereafter from handeling or from wrappers and usually initiate growth in the crease of the loaf and between the slices of sliced bread.

Chief mold involed in the spoilage of bread are the so-called bread mold,Rhizopus stolonifer (R. nigricans), with its white cottony mycelium and black dots of sporangia; the green- spored Penicillium expansum or P. stoloniferum, Aspergillus niger with its greenish or purplish-brown to black conidial heads and yellow pigment diffusing into the bread and Monilia (Neurospora) sitophila, whose pink conidia give a pink or reddish colour to its growth, Species of Mucor or Geotrichum or any of a large number of species  of other genera pf molds may develop.

Mold spoilage is favoured by :

Heavy contamination after baking , due  for example, to air heavily laden with mold spores, a long cooling time considerable air circulation, or a contamination alicing machine.

Slicing, in that more air is introduced into the loaf.

Wraping , especially if the bread is warm when wrapped and

Storage in a warm humid place.

Various methods are employed to prevent moldiness of bread:

1.Prevention of contamination of bread with mold spores insofar as practical: The air about the bread is kept low in spores by removal of possible breeding places for molds, such as returned bread, or walls and equipment.Filteration and washing of air to the room and irradiation of the room and more especially the air by means of ultraviolet rays cut down contamination.

2. Prompt and adequate cooling of the loaves before wrapping to reduce condensation of moisture beneth the wrapper.

3.Ultraviolet irradiation of the surface of the loaf and  of slicing knives.

Destruction of molds on the surface by electronic heating.

Keeping the bread cool to slow mold growth or freezing and storage in the frozen condition to prevent growth entirely.

Incorporation in the bread dought of some mycostatic chemical.

 

Rope

Ropiness of bread is fairly common in home-baked bread, especially during hot weather, but it is rare in commercially baked bread because of the preventive measures now employed.

Ropiness is caused by a mucoid variant of Bacillus subtilis or B. licheniformis formerly called B. mesentericus , B. panis, and other spp.

The spore of these species can with strand the  temperature of the bread during baking, which does not exceed 100C . and can germinate and grow in the loaf if conditions are favorable.

The ropy condition apparently is the result of capsulation of the bacillus together with hydrolysis of the flour proteins (gluten) by proteinases of the organism and of starch by amylase to give sugar that encourage rope formation.

The area of ropiness is yellow to brown in colo and is soft and sticky to the touch.

In one stage the slimy material can be drawn out into long thread when the bread is broken and pull apart .

The unpleasant odor is difficult to characterize although it has been described as that of decomposed or overripe melons. First the odor is evident, then discoloration, and finally softening of the crumb with stickiness and stringiness.

 

Red Bread:

Red or “Bloody” bread is stricking in appearance but are in occurance.

The red colour results from the growth of pigmented bacteria usually Serratia marcescens, an organism that oftern is brilliantly red or starch foods.

Molds such as Monilia ( Neurospora) sitophia, previsously mentioned may impart a pink to red color to bread. A red color in the crumb of dark bbread has been caused by Geotrichum aurantiacum

 

Chalky Bread:

 Chalky bread also uncommon is so named because of white , chalk like spots.

The defect has been blamed on the growth of yeast like fungi Endomycopsis fibuligera and Trichospora variable.

 

Refernce:

Food Microbiology  By William C. Frazier. Page no 330-331 & 180-184.

iii. Fruits and Vegetables

The main sources of microorganisms in vegetables are soil, water, air, and other environmental sources, and can include some plant pathogens.

Fresh vegetables are fairly rich in carbohydrates (5% or more), low in proteins (about 1 to 2%), and, except for tomatoes, have high pH. 

Microorganisms grow more rapidly in damaged or cut vegetables.

The presence of air, high humidity, and higher temperature during storage increases the chances of spoilage. 

The common spoilage defects are caused by molds belonging to genera Penicillium, Phytophthora, Alternaria, Botrytis, and Aspergillus. Among the bacterial genera, species from Pseudomonas, Erwinia, Bacillus, and Clostridium are important.

Microbial vegetable spoilage is generally described by the common term rot, along with the changes in the appearance, such as black rot, gray rot, pink rot, soft rot, stem-end rot .

Vegetables are another tempting source of nutrients for spoilage organisms because of their near neutral pH and high water activity. 

Although vegetables are exposed to a multitude of soil microbes, not all of these can attack plants and some spoilage microbes are not common in soil, for example, lactic acid bacteria.

Most spoilage losses are not due to microorganisms that cause plant diseases but rather to bacteria and molds that take advantage of mechanical and chilling damage to plant surfaces. 

Some microbes are found in only a few types of vegetables while others are widespread. Erwinia carotovora is the most common spoilage bacterium and has been detected in virtually every kind of vegetable. 

It can even grow at refrigeration temperatures . 

Bacterial spoilage first causes softening of tissues as pectins are degraded and the whole vegetable may eventually degenerate into a slimy mass. 

Starches and sugars are metabolized next and unpleasant odors and flavors develop along with lactic acid and ethanol. Besides E. carotovora, several Pseudomonas spp. and lactic acid bacteria are important spoilage bacteria.

Molds belonging to several genera, including Rhizopus, Alternaria and Botrytis, cause a number of vegetable rots described by their color, texture, or acidic products. 

The higher moisture content of vegetables as compared to grains allows different fungi to proliferate, but some species of Aspergillus attack onions.

Intact, healthy fruits have many microbes on their surfaces but can usually inhibit their growth until after harvest.

Ripening weakens cell walls and decreases the amounts of antifungal chemicals in fruits, and physical damage during harvesting causes breaks in outer protective layers of fruits that spoilage organisms can exploit. 

Molds are tolerant of acidic conditions and low water activity and are involved in spoilage of citrus fruits, apples, pears, and other fruits. Penicillium, Botrytis, and Rhizopus are frequently isolated from spoiled fruits.

Yeasts and some bacteria, including Erwinia and Xanthomonas, can also spoil some fruits and these may particularly be a problem for fresh cut packaged fruits .

Fruits juices generally have relatively high levels of sugar and a low pH and this favors growth of yeasts, molds and some acid-tolerant bacteria. 

Spoilage may be manifested as surface pellicles or fibrous mats of molds, cloudiness,and off-flavors. Lack of oxygen in bottled and canned drinks limits mold growth. Saccharomyces and Zygosaccharomyces are resistant to thermal processing and are found in some spoiled juices . 

Alicyclobacillus spp., an acidophilic and thermophilic spore-forming bacteria, has emerged as an important spoilage microbe, causing a smoky taint and other off-flavors in pasteurized juices Propionibacterium cyclohexanicum, an acidtolerant non-sporeforming bacterium also survives heating and grows in a variety of fruit juices . 

Lactic acid bacteria can spoil orange and tomato juices, and some pseudomonads and enterobacteriaceae also spoil juices.

These bacteria are not as heat tolerant but may be post-pasteurization contaminants colonization by many, but not all, microbes and are the most important first step in delaying the spoilage process. 

Microbes require certain conditions for growth, and therefore management of the environment of foods can change these factors and delay spoilage:

Many, but not all, microbes grow slowly or not at all at low temperatures, and refrigeration can prolong the lag phase and decrease growth rate of microbes. 

Many microbes require a high water activity and therefore keeping foods such as grains and cereal products dry will help to preserve them.

Some microbes require oxygen, others are killed by oxygen, and still others are facultative. 

Managing the atmosphere during storage in packaging can retard or prevent the growth of some microbes. 

Several types of modified atmosphere packaging (MAP) have been developed to retard growth of pathogenic and spoilage organisms. However, microbes are endlessly innovative and eventually seem to circumvent the barriers set against them. Therefore further strategies and multiple hurdles are utilized to extend shelf life. 

These procedures must be assessed for compatibility with different foods so that there are no significant organoleptic changes in the foods caused by the treatment or preservative.

iv. Eggs

Spoilage of eggs is promoted by cracking the eggshell, improper washing, and storage techniques.

The most predominate spoilage (rot) of shell eggs is caused by Gram‐negative motile rods: Pseudomonas, Proteus, Alcaligenes, Aeromonas, and coliforms.

Pasteurized egg products at refrigerated temperatures have limited shelf life, unless additional preservatives are used.

The predominant bacteria causing spoilage in pasteurized egg products are psychrotrophic Gram‐negative.

Dried eggs are not susceptible to microbial spoilage due to low water activity.

Examination of an unbroken egg with transmitted light using candle can identify grossly contamination of eggs or rotten egg. 

A great extent of pasteurization should be included during heat treatment of shell egg since the temperatures required for the killing of microorganisms are close to those at which the egg proteins coagulate. 

Fumigation of eggs with gaseous ethylene oxide before storage protects eggs against bacterial spoilage.

Characteristic and species involved in the spoilage of shell eggs:

The microflora of the eggshell is dominated by Gram-positive bacteria such as Staphylococcus, Streptococcus, Aerococcus and Micrococcus.

Other minor contaminants are Gram-negative bacteria, such as Salmonella, Escherichia and Alcaligenes sp., and also Gram-positive bacteria, such as Bacillus.

The main egg spoilage event is described as rotten egg, which appears as a coloured egg (black, blue, pink, red, green) mostly developing a rotten odour. 

The bacteria described as being involved are Pseudomonas, Proteus, Alcaligenes, Enterobacter, Serratia, Stenotrophomonas, Cloaca, Acinetobacter, Moraxella and Citrobacter spp. 

Other egg spoilage events are described as leading to a yellow pigmentation of the shell membranes, due to the action of Flavobacterium or Cytophaga species.  

Spoilage of egg products:

Because of their various functional properties (foaming, binding, gelling, or dying properties), the egg products are particularly used in the food industry and enter in the composition of a wide range of food, such as sauces, pasta, biscuits, cakes, processed meats, creams and refrigerated desserts.

The process of egg product manufacturing induces a systematic contamination of the egg content, since, once broken, the egg loses its natural antimicrobial defences.

Whole egg and egg yolk are indeed ideal environments for the development of microorganisms .

Species involved in spoilage and spoilage characteristics:

The predominant microorganisms surviving pasteurization are Gram-positive bacteria, such as Streptococci, Enterococci and Bacillus spores.

The predominant microorganisms surviving pasteurization are Gram-positive bacteria, such as Streptococci, Enterococci and Bacillus spores.

The spoilage of egg products is most commonly due to post-pasteurization contaminations by Gram-negative bacteria, such as Pseudomonas or Enterobacteriaceae

 The food spoilage due to non spore-forming psychrotolerant bacteria generally arises from inadequate heating or post-pasteurization contamination, that can be controlled by corrections of the pasteurization protocols and by improved sanitation processes. 

Therefore, excluding post-process contaminants, Bacillus species appear as one of the main flora involved in spoilage events in this sector. 

Even if Bacillus spores are present at low levels in both raw and pasteurized egg products, they resist the pasteurization step. 

The Bacillus genus, and notably the B. cereus group, is able to multiply in liquid whole egg where it causes enzymatic spoilage events. 

These ubiquitous bacteria are difficult to eliminate because of their heat-resistance and their strong adhering capacities, which allow them to form biofilms on industrial surfaces

v. Sea foods

 

Seafood is one of the most highly perishable food products because of the chemical effects of atmospheric oxygen and the growth of spoilage microorganisms .

Spoilage of seafood can be caused by enzymes, dehydration, oxidation, contamination and physical damage. Sulphurous, ammoniacal, or fishy odours are some of the main organoleptic changes taking place during spoilage development.

The major cause of seafood spoilage is microbial growth and metabolic activity which result in the formation of amines, sulphides, alcohols, aldehydes, ketones, and organic acids with unpleasant and unacceptable off-flavours.

However, only a fraction of the initial microbiota of seafood known as specific spoilage organisms (SSOs), which is favoured by storage conditions (e.g., atmosphere, temperature), prevails over the rest of the microbiota, reaching high populations and producing corresponding metabolites (biochemical spoilage indices).

Quorum sensing (QS), which involves the production, release and community-wide detection of extracellular signaling molecules called autoinducers, is a cell-to-cell communication process enabling microorganisms to collectively alter behavior patterns upon changes in cell density and species composition in surrounding community.

Main Spoilage Microorganisms in Different Seafood and Seafood Products are :

The recent establishment of the SSO concept has contributed significantly to our understanding of seafood spoilage .

The growth of different SSOs depends on several parameters: food product, type of preservation, temperature, atmosphere, and salt content, among others.

During storage, the microflora changes owing to different abilities of the microorganisms to tolerate the preservation conditions .

Here, the storage conditions of seafood were divided into two major categories, and the spoilage microorganisms predominant in both conditions were discussed and listed in Table 1, respectively.

Spoilage bacteria	Sea foods and seafood products
Shewanella spp.	Gutted sea bass
	Iced sea salmon
	Air stored swordfish
	Refrigerated shrimp
	Refrigerated large yellow croaker
Pseudomonas spp.	Gutted sea bass
	Air stored swordfish
Aeromonas spp.	Iced sea salmon
Photobacterim phosphoreum	MAP/VP stored raw salmon
	VP packaged squid mantle
Enterobacteriaceae	MAP/VP packaged swordfish
	VP packaged pressurised squid mantle
LAB	MAP/VP stored raw salmon
	MAP/VP packaged swordfish
	VP packaged pressurised squid mantle

vi. Canned foods

Canning is one of important method of packaging food for long term storage.

Normally food is stored in metallic containers along with heat treatment.

The heat treatment varies depending upon type of food.

There is always a chance that microorganisms may survive if the heat treatment is not proper thereby leading to spoilage of food.

Usually the incidences of food spoilage in cans are low.

The spoilage of can could be due to biological or chemical reasons or combination of both. 

The biological spoilage is primarily due to microbial growth while chemical spoilage is due to hydrogen produced due to reaction of acid in food and iron on can.

The degree of swelling can also be increased by high summer temperature and high altitudes. Certain other factors such as overfilling, buckling, denting or closing the can while cool may also be responsible for spoilage of foods in cans.

Causes of Spoilage in Cans: 

1.Chemical spoilage

The chemical spoilage in most cases is due to production of hydrogen gas produced in can because of action of acid of food on iron of can.

This spoilage is termed as Hydrogen swell. It occurs due to following factors:

a) Increased storage temperature.

b) Increased acidity of food

c) Improper exhaust

d) Presence of soluble sulfur and phosphorous compounds

e) Improper timing and lacquering of can at internal surfaces

2 Biological spoilage

The cause of biological spoilage is microbial activity. In heat treated cans, the growth of microorganisms occur due to:

a) Leakage of can

It occurs because of manufacturing defects, punctures or rough handling. Bacteria are introduced into can by either in holes or improper seams. 

In this type, the microorganisms are not usually heat resistant and wide array of organisms had been found to cause spoilage as it is post processing contamination.

Microbes may also get entry into can due to cold water, used to cool cans after heat treatment.

Leakage may also be responsible for release of vacuum, which can favor the growth of microorganisms.

Presence of low heat resistance organisms usually indicates leakage of can.

b) Under processing

It includes sub-optimal heat treatment, faulty retort operations, excessive microbial load and contamination in product, change in consistency of the product.

3 Stages in Appearance of Can

A can undergo different transformations from being a normal can to completely spoilt can as it depend upon various factors. 

4 Microbial Spoilage of Canned Foods

The microbial spoilage of canned food is classified as caused by thermophilic bacteria and mesophilic organisms. 

Most common spoilages of microbial origin are known as flat sour spoilage, Thermophilic anaerobic (TA) spoilage and putrefaction.

These different types are briefly described here.

a) Spoilage by thermophilic spore forming bacteria

Spoilage by these types of bacteria is most prevalent in under processed heat treated canned foods.

Their spores survive the heat treatment and undergo vegetative cell formation and subsequent growth in canned conditions. 

Major spoilages by these organisms are:

b)Flat sour spoilage

This is caused by souring bacteria.

One characteristic of this spoilage is that ends of can remain flat during souring. 

Because of this condition, the detection of spoilage from outside is not possible thereby culturing of contents become necessary to detect the type of organisms.

Main organisms involved are Bacillus, while it occurs more frequently in low acid foods. Bacillus spp. has ability to produce acid without gas formation.

c) TA spoilage

This type of spoilage is caused by thermophilic anaerobe not producing hydrogen sulfide. 

Clostridium thermosaccharolyticum is the main organism involved. 

It produces acid and gas in foods. Spoiled food produces sour or cheesy smell.

d) Sulfur stinker spoilage

This type of spoilage occurs in low acid foods and primarily Desulfotomaculum nigricans is involved.

The spores of these organisms are destroyed at optimal heat treatment, thus presence of this organism usually indicates under processing in terms of heat treatment.

It produces hydrogen sulfide which produce typical odour.

5 Spoilage By Mesophillic Spore formers

Bacillus and Clostridium are involved in this type of spoilage which is usually indicative of under spoilage.

6 Spoilage by Non-Spore Formers

Presence of non spore formers in cans indicate post processing contamination.

The organisms whose vegetative cells are heat resistant are more readily found.

Following organisms are more prominent:

Enterococcus	Streptococcus thermophilus
Micrococcus	Lactobacillus
Leuconostoc	Microbacterium

Presence of these organisms indicates leakage of container.

Cooling water is one of the important source of contamination, thus coilforms also gain entry into the can through leakage.

7 Spoilage by Fungi

1 Yeasts

Yeasts and their spores are not thermo tolerant, thus they are not found in suitably heat treated cans.

Their presence indicates under processing or post pasteurization contamination through leakage.

Fermentative yeasts are more prominent and they produce carbon dioxide, thus causing swelling of cans.

Film yeasts too can grow on the surface of the food products.

2 Molds

Among molds, Aspergilus and Penicillium are most spoiling organisms.

These can grow at high sugar concentration.

Acidification is considered method of preventing growth of molds.

Some of the molds are resistant to heat.

Molds are more common in home canned foods where heating as well as sealing is not under total aseptic conditions.