There are three types: bacteria, moulds and yeasts. Bacteria and yeasts
cannot be seen with the naked eye, but moulds are often visible because they form
visible thin threads (filaments) or a solid cluster. Just like humans,
micro-organisms require certain minimum living conditions. They
cannot survive without:
* sufficient water
* oxygen
* the right degree of acidity
* nutrients
* the right temperature
Water is essential for maintaining many physical processes. Where
there is a shortage or lack of water micro-organisms cannot grow, such
as in dried legumes. Drying is therefore one way to prevent spoilage.
Meat and fish do not have to be 100% dry in order to preserve them.
By adding salt, the remaining water becomes unsuitable for microorganisms.
The same effect can be achieved by adding sugar to fruit.
Enzymatic spoilage is also inhibited by drying.
Most micro-organisms need oxygen. If there is a shortage of oxygen,
it is difficult for bacteria to survive, let alone multiply. But there are
always a few that manage to survive. As soon as the oxygen supply is
increased, these remaining bacteria will again grow and multiply.
Some types of micro-organisms even thrive in an oxygen-poor environment.
Bacteria grow best in an environment that is not too acidic. Less
acidic products are therefore especially susceptible to bacterial spoilage.
Examples of such products are meat, eggs, milk and various types
of vegetables. Beer, yoghurt, wine, vinegar and fruit are less sensitive
because they are more acidic. Adding acidity to products slows down
the process of microbial spoilage. The degree of acidity is measured as
a pH level. A neutral product like milk has a pH of 7; meat has a pH of
about 6, carrots have a pH of 5 and oranges about 4. The more acidic a
product is, the lower the pH value will be.
Just like humans, micro-organisms also need nutrients: sugars, proteins,
fats, minerals and vitamins. These are rarely in short supply,
because they can be found in all food products.
To thrive, micro-organisms need a temperature of between 5 and
65°C. At temperatures above 65°C it becomes very difficult for them
to survive; and they definitely die if boiled, as long as they are boiled
for a certain length of time, such as 10 minutes. When heated, the
micro-organisms slowly die off, but not all at the same time. Heating
at temperatures lower than 100°C thus has to be sustained for a longer
period. The growth of micro-organisms is also slowed down significantly
at temperatures between 0 and 5°C (as in a refrigerator), which
makes it possible to store the food products for a few additional days.
At temperatures below 0°C microbial growth is stopped completely,
but the micro-organisms themselves remain alive. They will become
active again as soon as the temperature rises above 0°C.
To preserve food, it is sometimes necessary to make drastic changes to
the micro-organisms’ living conditions. We can remove water (drying),
increase the acidity, or first heat the products (to kill the bacteria)
and then store them in air-tight containers to prevent oxygen from
entering (preserving/canning). These and other methods will be discussed
later in this booklet.
Do micro-organisms grow differently on vegetables and fruit?
Vegetables and fruit have a lot in common. But there are also important
differences, which determine the type of spoilage they are most
susceptible to. Damaged fruits, which are usually somewhat acidic,
are very susceptible to the growth of yeasts and moulds. Vegetables
are generally less acidic, and their spoilage is usually caused by bacteria.
Though not visible to the naked eye, bacteria can still be present
in large numbers.
Sunday, October 17, 2010
What is food spoilage
Every change in food that causes it to lose its desired quality and
eventually become inedible is called food spoilage or rotting. As noted
earlier, this Agrodok focuses specifically on fruits and vegetables. As
long as they are not harvested, their quality remains relatively stable –
if they are not damaged by disease or eaten by insects or other animals.
However, the harvest cannot be postponed indefinitely: when
the time is right, it is time to act. As soon as the fruits and vegetables
are cut off from their natural nutrient supply, their quality begins to
diminish. This is due to a natural process that starts as soon as the
biological cycle is broken by harvesting. Once it is harvested, the agricultural
product is edible for only a limited time, which can vary from
a few days to weeks. The product then begins to spoil or ‘rot’. We
distinguish between various types of spoilage:
1 physical spoilage
2 physiological aging
3 spoilage due to insects or rodents
4 mechanical damage
5 chemical and enzyme spoilage
6 microbial spoilage
Physical spoilage is caused for example by dehydration. Physiological
aging occurs as soon as the biological cycle is broken through harvesting.
Neither process can be prevented, but they can be delayed by storing
the agricultural products in a dry and draft-free area at as low a
temperature as possible.
Insects and rodents can cause a lot of damage. Not only by eating the
products, but also by passing on micro-organisms through their hair
and droppings. The affected parts of the plants are then especially
susceptible to diseases.
Chemical and enzyme spoilage occurs especially when vegetables and
fruit are damaged by falling or breaking. Such damage can release
enzymes that trigger chemical reactions. Tomatoes become soft, for
example, and apples and other types of fruit turn brown. The fruit can
also become rancid. The same processes can also be triggered by insects:
the fruit becomes damaged, which causes enzymes to be released.
Enzymes can be deactivated by heating the fruit or vegetables.
The same effect can be achieved by making the fruit or vegetables
sour or by drying them, but the enzymes become active again as soon
as the acidity is reduced or water is added.
The peel of a fruit or vegetable provides natural protection against
micro-organisms. As soon as this shield is damaged by falling, crushing,
cutting, peeling or cooking, the chance of spoilage increases considerably.
Crushing occurs most often when fruits or vegetables are
piled up too high.
To prevent harvested products from spoiling, they can be preserved:
physiological aging and enzyme changes are then stopped and microorganisms
are prevented from multiplying on the product. To retain
the desired quality of a product longer than if it were simply stored
after harvesting, it must be preserved. To preserve food it must first be
treated, with the goal of stopping physiological aging and enzyme
changes and preventing the growth of micro-organisms.
Before discussing the specific treatment methods, we will first focus
on the subject of micro-organisms. What are micro-organisms? Why
are they dangerous? How can you prevent them from making you
sick? The answers to these questions will help you understand the
steps required to safely preserve food.
eventually become inedible is called food spoilage or rotting. As noted
earlier, this Agrodok focuses specifically on fruits and vegetables. As
long as they are not harvested, their quality remains relatively stable –
if they are not damaged by disease or eaten by insects or other animals.
However, the harvest cannot be postponed indefinitely: when
the time is right, it is time to act. As soon as the fruits and vegetables
are cut off from their natural nutrient supply, their quality begins to
diminish. This is due to a natural process that starts as soon as the
biological cycle is broken by harvesting. Once it is harvested, the agricultural
product is edible for only a limited time, which can vary from
a few days to weeks. The product then begins to spoil or ‘rot’. We
distinguish between various types of spoilage:
1 physical spoilage
2 physiological aging
3 spoilage due to insects or rodents
4 mechanical damage
5 chemical and enzyme spoilage
6 microbial spoilage
Physical spoilage is caused for example by dehydration. Physiological
aging occurs as soon as the biological cycle is broken through harvesting.
Neither process can be prevented, but they can be delayed by storing
the agricultural products in a dry and draft-free area at as low a
temperature as possible.
Insects and rodents can cause a lot of damage. Not only by eating the
products, but also by passing on micro-organisms through their hair
and droppings. The affected parts of the plants are then especially
susceptible to diseases.
Chemical and enzyme spoilage occurs especially when vegetables and
fruit are damaged by falling or breaking. Such damage can release
enzymes that trigger chemical reactions. Tomatoes become soft, for
example, and apples and other types of fruit turn brown. The fruit can
also become rancid. The same processes can also be triggered by insects:
the fruit becomes damaged, which causes enzymes to be released.
Enzymes can be deactivated by heating the fruit or vegetables.
The same effect can be achieved by making the fruit or vegetables
sour or by drying them, but the enzymes become active again as soon
as the acidity is reduced or water is added.
The peel of a fruit or vegetable provides natural protection against
micro-organisms. As soon as this shield is damaged by falling, crushing,
cutting, peeling or cooking, the chance of spoilage increases considerably.
Crushing occurs most often when fruits or vegetables are
piled up too high.
To prevent harvested products from spoiling, they can be preserved:
physiological aging and enzyme changes are then stopped and microorganisms
are prevented from multiplying on the product. To retain
the desired quality of a product longer than if it were simply stored
after harvesting, it must be preserved. To preserve food it must first be
treated, with the goal of stopping physiological aging and enzyme
changes and preventing the growth of micro-organisms.
Before discussing the specific treatment methods, we will first focus
on the subject of micro-organisms. What are micro-organisms? Why
are they dangerous? How can you prevent them from making you
sick? The answers to these questions will help you understand the
steps required to safely preserve food.
The Food spoilage: causes, effects and prevention
Every change in food that causes it to lose its desired quality and
eventually become inedible is called food spoilage or rotting. As noted
earlier, this Agrodok focuses specifically on fruits and vegetables. As
long as they are not harvested, their quality remains relatively stable –
if they are not damaged by disease or eaten by insects or other animals.
However, the harvest cannot be postponed indefinitely: when
the time is right, it is time to act. As soon as the fruits and vegetables
are cut off from their natural nutrient supply, their quality begins to
diminish. This is due to a natural process that starts as soon as the
biological cycle is broken by harvesting. Once it is harvested, the agricultural
product is edible for only a limited time, which can vary from
a few days to weeks. The product then begins to spoil or ‘rot’. We
distinguish between various types of spoilage:
1 physical spoilage
2 physiological aging
3 spoilage due to insects or rodents
4 mechanical damage
5 chemical and enzyme spoilage
6 microbial spoilage
Physical spoilage is caused for example by dehydration. Physiological
aging occurs as soon as the biological cycle is broken through harvesting.
Neither process can be prevented, but they can be delayed by storing
the agricultural products in a dry and draft-free area at as low a
temperature as possible.
Insects and rodents can cause a lot of damage. Not only by eating the
products, but also by passing on micro-organisms through their hair
and droppings. The affected parts of the plants are then especially
susceptible to diseases.
Chemical and enzyme spoilage occurs especially when vegetables and
fruit are damaged by falling or breaking. Such damage can release
enzymes that trigger chemical reactions. Tomatoes become soft, for
example, and apples and other types of fruit turn brown. The fruit can
also become rancid. The same processes can also be triggered by insects:
the fruit becomes damaged, which causes enzymes to be released.
Enzymes can be deactivated by heating the fruit or vegetables.
The same effect can be achieved by making the fruit or vegetables
sour or by drying them, but the enzymes become active again as soon
as the acidity is reduced or water is added.
The peel of a fruit or vegetable provides natural protection against
micro-organisms. As soon as this shield is damaged by falling, crushing,
cutting, peeling or cooking, the chance of spoilage increases considerably.
Crushing occurs most often when fruits or vegetables are
piled up too high.
To prevent harvested products from spoiling, they can be preserved:
physiological aging and enzyme changes are then stopped and microorganisms
are prevented from multiplying on the product. To retain
the desired quality of a product longer than if it were simply stored
after harvesting, it must be preserved. To preserve food it must first be
treated, with the goal of stopping physiological aging and enzyme
changes and preventing the growth of micro-organisms.
Before discussing the specific treatment methods, we will first focus
on the subject of micro-organisms. What are micro-organisms? Why
are they dangerous? How can you prevent them from making you
sick? The answers to these questions will help you understand the
steps required to safely preserve food.
eventually become inedible is called food spoilage or rotting. As noted
earlier, this Agrodok focuses specifically on fruits and vegetables. As
long as they are not harvested, their quality remains relatively stable –
if they are not damaged by disease or eaten by insects or other animals.
However, the harvest cannot be postponed indefinitely: when
the time is right, it is time to act. As soon as the fruits and vegetables
are cut off from their natural nutrient supply, their quality begins to
diminish. This is due to a natural process that starts as soon as the
biological cycle is broken by harvesting. Once it is harvested, the agricultural
product is edible for only a limited time, which can vary from
a few days to weeks. The product then begins to spoil or ‘rot’. We
distinguish between various types of spoilage:
1 physical spoilage
2 physiological aging
3 spoilage due to insects or rodents
4 mechanical damage
5 chemical and enzyme spoilage
6 microbial spoilage
Physical spoilage is caused for example by dehydration. Physiological
aging occurs as soon as the biological cycle is broken through harvesting.
Neither process can be prevented, but they can be delayed by storing
the agricultural products in a dry and draft-free area at as low a
temperature as possible.
Insects and rodents can cause a lot of damage. Not only by eating the
products, but also by passing on micro-organisms through their hair
and droppings. The affected parts of the plants are then especially
susceptible to diseases.
Chemical and enzyme spoilage occurs especially when vegetables and
fruit are damaged by falling or breaking. Such damage can release
enzymes that trigger chemical reactions. Tomatoes become soft, for
example, and apples and other types of fruit turn brown. The fruit can
also become rancid. The same processes can also be triggered by insects:
the fruit becomes damaged, which causes enzymes to be released.
Enzymes can be deactivated by heating the fruit or vegetables.
The same effect can be achieved by making the fruit or vegetables
sour or by drying them, but the enzymes become active again as soon
as the acidity is reduced or water is added.
The peel of a fruit or vegetable provides natural protection against
micro-organisms. As soon as this shield is damaged by falling, crushing,
cutting, peeling or cooking, the chance of spoilage increases considerably.
Crushing occurs most often when fruits or vegetables are
piled up too high.
To prevent harvested products from spoiling, they can be preserved:
physiological aging and enzyme changes are then stopped and microorganisms
are prevented from multiplying on the product. To retain
the desired quality of a product longer than if it were simply stored
after harvesting, it must be preserved. To preserve food it must first be
treated, with the goal of stopping physiological aging and enzyme
changes and preventing the growth of micro-organisms.
Before discussing the specific treatment methods, we will first focus
on the subject of micro-organisms. What are micro-organisms? Why
are they dangerous? How can you prevent them from making you
sick? The answers to these questions will help you understand the
steps required to safely preserve food.
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