¡@
¡@
¡@
¡@
The need to preserve
food
spoiled crop
Food Preservation , processes
involved in protecting food against microbes and other spoilage
agents to permit its future consumption. The preserved food
should retain a palatable appearance, flavor, and texture, as
well as its original nutritional value.
The following frour points are
the main reasons of food presevation:
- To protect food against microbes and other spoilage
agents
- To ensure that food is safe for future consumption
- To prolong food storage time
- To allow many foods to be available year-round, in great
quantity and the best-quality
[back to top]
Principles of
preservations
Micro-organisms, enzyme, chemical reaction of food components
are the main causes of food spoilage.
So the principles of preservations are:
Killing of
micro-organisms
Inhibition of
microbial growth
Removing
micro-organisms
Destroying enzyme
Retardation of
chemical changes
[back to top]
Conditions
for the growth of micro-organisms
Suitable
Temperature
: Some micro-organisms can grow at 50 - 60oC ;
others have optimum growth temperatures of 25 - 40oC
, and others grow well at 10 - 20oC, and
survive at 0oC ;
pH
value : Most
micro-organisms grow best at a pH of 6.6 to 7.5. Some
micro-organisms grow at lower pH values. The spoilage of
fruits is usually caused by yeasts and moulds, which can
tolerate low pH. The spoilage of meat and fish is usually
caused by bacteria ;
- Moisture
( water activity of the food ) : The water activity of a food
describes the amount of available water in a food. It is
given by:
water activity = (water
vapour pressure above the food at a certain temperature) /
(water vapour pressure above pure water at the same
temperature)
The micro-organisms cannot
grow with the water activity less than 0.6 ;
- Nutrients : to supply energy, to supply
nitrogen for protein synthesis and minerals ;
- Time : Some bacteria divide onec every 20
minutes. If the food supply were adequate, a single
bacterium could produce 2 million offspring in 7 hours.
The growth rate declines as the food supply is exhausted
;
- A suitable
atmosphere : Some
micro-organisms such as mould and some bacteria cannot
thrive in absence of oxygen. Yest and and few bacteria
can thrive in either the presence or the absence of
oxygen.
[back to top]
¡@
Ways of
the prevention and their side effects
[back to top]
