As you can now very well understand the heat is an important way of
preserving foods. Still some thermally processed foods undergo spoilage due to
chemical or biological reasons. The most important chemical spoilage of
canned foods is the hydrogen swell produced as a result of action of food acids
with the metals.
Biological spoilage of thermally processed foods by
microorganisms may result either from the survival of organisms after the heat
treatment or leakage of the container permitting entrance of the
microorganisms. Surviving organisms may be vegetative cells or spore formers
depending upon the heat treatment. Acid foods are processed at temperature
around 100OC which result in the killing of all vegetative cells of bacteria,
yeasts and molds.
Only bacterial spores may survive stearothermophilus is a
non-pathogenic organism that has been shown to be one but these do not grow
in acid foods. On the other hand, meat, vegetables and milk are processed at
low temperatures. This may eliminate vegetative cells but not the spores,
which germinate later and cause spoilage. Microorganisms that enter through
leaks during cooling need not necessarily be heat resistant
Spoilage by Thermophilic Bacteria
Under processing of low acid foods result in spoilage by thermophilic
(microorganisms which require high temperature, more than 45°C for their
growth) bacteria such as Bacillus coagulance, Bacillus stereothermophilus.
These microbes produce heat resistant endospores than can survive 121°C for
4-5 minutes. These organisms produce acid without gas. This is known as flat
sour spoilage.
(microorganisms which require high temperature, more than 45°C for their
growth) bacteria such as Bacillus coagulance, Bacillus stereothermophilus.
These microbes produce heat resistant endospores than can survive 121°C for
4-5 minutes. These organisms produce acid without gas. This is known as flat
sour spoilage.
Some times In Low and medium acid foods the cans swell due
to production of carbon dioxide and hydrogen by Clostridium
thermosaccharolyticum. This is known as thermophilic spoilage. Sulphide
spoilage is caused by Clostridium nigrificans in low acid foods.
to production of carbon dioxide and hydrogen by Clostridium
thermosaccharolyticum. This is known as thermophilic spoilage. Sulphide
spoilage is caused by Clostridium nigrificans in low acid foods.
Spores of this
bacterium are not very heat resistant and their presence is indicative of under
processing. Spoilage is indicated by the the presence of H2S and blackening of
material. Sources of all these material are generally, the plant equipment,
sugar, starch, soil etc.
bacterium are not very heat resistant and their presence is indicative of under
processing. Spoilage is indicated by the the presence of H2S and blackening of
material. Sources of all these material are generally, the plant equipment,
sugar, starch, soil etc.
Spoilage by Mesophilic Organisms
Mesophilic microorganisms are those microorganisms which grow best at
temperature 25-45°C. Spoilage of canned foods by mesophilic organisms is
indicative of under processing and is caused by species of Bacillus,
Clostridium, Yeast and fungi. Clostridium butyricum and C. pasteurianum
produce a butyric acid type of fermentation in acid or medium acid foods with
swelling of the container by the production of CO2 and H2.
temperature 25-45°C. Spoilage of canned foods by mesophilic organisms is
indicative of under processing and is caused by species of Bacillus,
Clostridium, Yeast and fungi. Clostridium butyricum and C. pasteurianum
produce a butyric acid type of fermentation in acid or medium acid foods with
swelling of the container by the production of CO2 and H2.
Other species of
Clostridia may produce H2S causing can to swell. These putrefactive
anaerobes (Micro organism that grow in the absence of oxygen) generally
grow in low acid foods such as peas corn, meat, poultry etc. but some times
may also spoil medium acid foods.
Clostridia may produce H2S causing can to swell. These putrefactive
anaerobes (Micro organism that grow in the absence of oxygen) generally
grow in low acid foods such as peas corn, meat, poultry etc. but some times
may also spoil medium acid foods.
Some Bacilli such as Bacillus subtilis and B. mesentroides have been found to
grow in poorly evacuated cans of sea foods, meat and milk. The gas forming
Bacilli (B.polymyxa, B. macerans) are also reported to cause spoilage of
canned peas, spinach, peaches and tomatoes.
grow in poorly evacuated cans of sea foods, meat and milk. The gas forming
Bacilli (B.polymyxa, B. macerans) are also reported to cause spoilage of
canned peas, spinach, peaches and tomatoes.
The presence of non spore forming bacteria in canned food is an indicative of
leak or under processing. Streptococcus thermophilus, Pseudomonas,
Micrococcus and proteus have also been reported to cause spoilage of
thermally processed products.
leak or under processing. Streptococcus thermophilus, Pseudomonas,
Micrococcus and proteus have also been reported to cause spoilage of
thermally processed products.
Molds, yeast and their spores are destroyed at
pasteurization temperature. Their presence is indicative of under processing or
leakage. Spoilage of canned fruits and fruit products by yeasts may result in
CO2 production and spoilage of cans. Film yeast and fungi grow on the surface
and cause degradation of the product.
pasteurization temperature. Their presence is indicative of under processing or
leakage. Spoilage of canned fruits and fruit products by yeasts may result in
CO2 production and spoilage of cans. Film yeast and fungi grow on the surface
and cause degradation of the product.
ANSWERS TO CHECK YOUR PROGRESS
EXERCISES
Check You Progress Exercise 1
1. Your answer should include the following points:
• Microorganisms that spoil product are typically called spoilage
organisms.
organisms.
• Microorganisms that can make people sick are pathogens.
2. Your answer should include the following points:
• to keep the food in a stable condition over a period of time
• to prevent it from spoilage or making people sick.
3. Your answer should include the following points:
• chemical preservation
• modified atmospheres
• irradiation
• low temperature preservation
• preservation by drying
• high temperature preservation
4. Your answer should include the following points:
• Time-temperature combination
• heat penetration characteristics of particular food
• the type of micro-organisms present in the food material
• the thermal death time of different microorganisms
• type of food
• concentration of the microorganisms
• state of the microorganism
• effect of heat on the product
• the degree of heat penetration
• food acidity / pH value.
Check You Progress Exercise 2
1. Your answer should include the following points:
• complete destruction of micro-organisms.
2. Your answer should include the following points:
• the condition achieved by the application of heat sufficient to render the
processed product free from viable microorganisms
processed product free from viable microorganisms
• capable of growing in the food under normal non-refrigerated
temperatures at which the food is likely to be held during distribution
and storage
temperatures at which the food is likely to be held during distribution
and storage
• Unlike sterilization here the food is not completely free of
microorganisms.
microorganisms.
Check You Progress Exercise 3
1. Your answer should include the following points:
• process created by Louis Pasteur
• aimed to destroy bacteria, molds, spores etc.
• discovery about the destruction of bacteria by exposing them to certain
minimum temperature for certain minimum time
minimum temperature for certain minimum time
• the higher the temperature the shorter the exposure time required.
• process applied to milk.
2. Your answer should include the following points:
• Public Health Aspect − to make milk and milk products safe for human
consumption by destroying all bacteria that may be harmful to health
(pathogens)
consumption by destroying all bacteria that may be harmful to health
(pathogens)
• Keeping Quality Aspect − to improve the keeping quality of milk and
milk products. Pasteurization can destroy some undesirable enzymes
and many spoilage bacteria. Shelf life can be 7, 10, 14 or up to 16 days.
milk products. Pasteurization can destroy some undesirable enzymes
and many spoilage bacteria. Shelf life can be 7, 10, 14 or up to 16 days.
3. Your answer should include the following point:
• extent of microbial inactivation depends on the combination of
temperature and holding time.
temperature and holding time.
4. Your answer should include the following points:
• Through pasteurization all of the bacteria are not completely destroyed,
it still exists in pasteurized products, but in very low concentrates.
it still exists in pasteurized products, but in very low concentrates.
• Refrigeration keeps the bacteria from further growth, very low.
5. Your answer should include the following points:
• thermal death time studies for the most heat resistant pathogens found
in milk
in milk
• Coxiella burnetii and Mycobacterium tuberculosis are the most heat
resistant non spore forming pathogens.
resistant non spore forming pathogens.
6. Your answer should include the following points:
• bacterial destruction is very nearly equivalent in LTLT and in HTST
pasteurization processes but
pasteurization processes but
• HTST treatment give the best quality products in respect of flavour and
vitamin retention.
vitamin retention.
Check You Progress Exercise 4
1. Your answer should include the following points:
• moisture increases the rate of heat penetration.
• Moist heat requires less heat (temperature or time) than dry heat
• 121°C for 10 min of moist heat is equivalent to about 30 min at 200°C
of dry heat.
of dry heat.
2. Your answer should include the following points:
• D-value is the amount of time that it takes at a certain temperature to
kill 90% of the organisms being studied.
kill 90% of the organisms being studied.
• Z value is defined as the temperature change required to change the Dvalue by a factor of 10.
• D-value gives us the time needed at a certain temperature to kill an
organism
organism
• Z-value relates the resistance of an organism to differing temperatures.
3. Your answer should include the following points:
• process based on the assumption of the number of surviving spores in
one can.
one can.
• canned foods subjected to a time/temperature process that will reduce
the probability of the survival of the most heat-resistant C. botulinum
spores by 12 logs i.e. from 1,000,000 to 0.0000001.
the probability of the survival of the most heat-resistant C. botulinum
spores by 12 logs i.e. from 1,000,000 to 0.0000001.
4. Your answer should include the following point:
• killing effect of a time / temperature combination
Check You Progress Exercise 5
1. Your answer should include the following point:
• Under processing or leakage may be the cause of spoilage of thermally
treated foods.
treated foods.
2. Your answer should include the following point:
• Bacillus coagulance and Bacillus stereothermophilus.
3. Your answer should include the following point:
• In Low and medium acid foods the cans swell due to production of
carbon di oxide and Hydrogen by Clostridium thermosaccharolyticum.
carbon di oxide and Hydrogen by Clostridium thermosaccharolyticum.
4. Your answer should include the following points:
• caused by Clostridium nigrificans in low acid foods.
• Spores of Clostridium nigrificans are not very heat resistant and their
presence is indicative of under processing
presence is indicative of under processing
• Spoilage is indicated by the the presence of H2S and blackening of
material.
material.
• Sources of all these material are generally, the plant equipment, sugar,
starch, soil etc
starch, soil etc
5. Your answer should include the following points:
• Clostridium nigrificans
• C. pasteurianum
• Bacillus subtilis
• B. mesentroides
• B.polymyxa
• B. macerans
• Streptococcus thermophilus
• Pseudomonas
• Micrococcus and Proteus.