Food is the basic necessity of man and is invaluable for healthy existence. However, most foods fit for consumption undergo deterioration and spoilage. In order to combat this problem foods have to be preserved.
Food preservation can be defined as the science that deals with the process of prevention of decay or spoilage of food thus allowing it to be stored in a fit condition for future use. Preservation of food increases the shelf life of foods and thus ultimately ensures its supply during times of scarcity and natural drought.
Food spoilage is a state in which food is deprived of its good or effective qualities. Deterioration or spoilage starts from the time food is harvested slaughtered or manufactured and results in undesirable changes in the physical and chemical characteristics of food.
Causes of food spoilage :
· Growth and activity of microorganisms such as bacteria, yeast and moulds.
· Activities of food enzymes and other chemical reactions within the food.
· Inappropriate temperatures for a given food.
· Gain or loss of moisture.
· Reaction with oxygen and light.
· Physical stress or abuse.
· Insects and rodents.
Non-enzymatic reactions in food such as oxidation and mechanical damage.
PRINCIPLES OF FOOD PRESERVATION
1. Prevention or delay of microbial decomposition.
a) by keeping out micro organisms (asepsis)
b) by removal of micro organisms (eg. filtration)
c) by hindering the growth and activity of micro organisms. (eg.) refrigeration, dehydration, addition of chemical preservatives.
d) by killing micro organisms. (eg.) boiling, irradiation.
2. Prevention or delay of self-decomposition of food.
a) by destruction or inactivation of enzymes. eg. by blanching. The steaming or boiling of fruits or vegetables in water for few minutes to inactivate natural enzymes and facilitates removal of skin is known as blanching.
b) by prevention or delay of purely chemical reactions. eg. prevention of oxidation by the use of anti-oxidants.
3. Prevention of damage caused by insects, animals and mechanical causes.
METHODS OF FOOD PRESERVATION
A perusal of the history of food preservation reveals that food preservation had its beginning from time immemorial and could be traced to nearly a thousand years ago.
Salting of meat, fish, and vegetables was the oldest method of preservation and could be traced back to the ancient Egypt and Greek civilisations.
Pickling in salt and vinegar, sun-drying and preservation of fruits and vegetables in sugar and honey were among the other methods used.
Storage of food in frozen conditions was also practiced for centuries in places where freezing temperatures were recorded.
The discovery of canning as a standard technique of preserving foods in sealed containers subject to high temperature was established in 1810 by Nicholas Appert. Around 1860, Louis Pasteur discovered that microbes were the main cause of spoilage and introduced a heat treatment known as pasteurisation to the world.
All methods used for food preservation are based on preventing or retarding the cause of spoilage.
When growth of micro organism is only retarded, preservation is temporary. When spoilage organisms are completely destroyed a more permanent preservation is achieved.