|
|
Whether
raw or processed, food is rarely sterile when it reaches the consumer.
It usually contains bacteria or other microbes, most of which are
harmless. Occasionally, it may also contain pathogenic microbes, which
could potentially be a threat to food safety.
The internal tissues of plants and animals have many defences to keep
microbes at bay, with the result that healthy, freshly-harvested crop
plants and fresh meat are usually sterile. However, changes after
harvesting or slaughter, or during processing, may allow microbes
to enter the food. These may originate from the crop plant or animal
itself, from the environment, the factory environment (via soil or
animals such as insects, birds and rodents) or from human sources.
Most food spoilage is due to microbial activity. Whilst spoilage does
not necessarily make food unsafe to eat, it can make it unpalatable.
Examples which pose little health risk are the moulds which can ruin
the appearance of fruits and broad; yeast and lactic acid bacteria
which can spoil sauces and beverages; and slime produced by microbes
which can make chilled meat look unappetising.
The World Health Organisation reports that, in spite of advances in
modern technology and efforts to provide safe food, foodborne diseases
remain a major public health concern both in developed and developing
countries. In the UK, for example, foodborne illness affected one in
every 1000 in 1992, double the number of reported cases in 1987, In
Sweden in 1992, there were more than 5000 reported cases of salmonellosis
alone. While more accurate reporting may account for some of the recent
increases in reported cases, it is clear that foodborne illness remains
a problem. There are two main categories of foodborne illness:
Infections
These result from eating food containing pathogenic microbes which then
multiply in the body. There are two types:
- Infections where the microbes attack the intestines or other organs
directly, causing symptoms such as nausea, vomiting, diarrhoea and
fever. Here, there may be a gap of several days between eating the
infected food and the appearance of symptoms, due to the time taken
for the microbe to multiply. Examples are the infections caused
by the bacteria Salmonella, Campylobacter and Listeria monacytogenes.
- Infections where symptoms such as diarrhoea result from poisons
or toxins produced by the microbes as they grow in the intestine.
Here, the time taken for symptoms to appear can vary from several
hours to several days after eating infected food. An example is the
illness caused by a toxic strain of the bacterium, Escherichia coli.
Intoxications
These result from eating food which contains toxins produced by
microbes which do not need to grow in the human body to cause illness.
symptoms can begin only a few hours after eating contaminated food.
An example is botulism, caused by a toxin from the bacterium Clostridium
botulinum.  |
|
