1. FOOD PRESERVATION BY SALT, ACID, SUGAR AND CHEMICAL PRESERVATION

2. SALT AND ACID
Salt was used by man as one of the earliest methods of food preservation.
Smoking and drying is used extensively in combination with salt, particularly for meat and fish product.
Salt and acid are use extensively in the preservation of vegetable product of which cucumbers, cabbage, and onions are important examples.

3. ANTI-MICROBIAL PROPERTIES OF SALT AND ACID
Salt produces a number of effects when added to fresh plant tissues
Salt exerts a selective inhibitory action on certain contaminating microorganisms.
Salt also affects the water activity (aw) of the substrate, thus controlling microbial growth by a method independent of its toxic effects.

4. Acids, chiefly acetic and lactic, can be present in preserved foods as a result of acid addition to non-fermented foods, or as a result of microbial fermentation of tissue carbohydrates.
Acids have two anti-microbial effects : one is due to their effect in pH, and the other is the specific toxicity of the undissociated acid which carries for different acids.

5. SUGAR
Sugar are involved in the preservation and manufacture of wide range of food products.
Some of the more common include : jams, jellies, fruit juice concentrates, sweetened condensed milk.
When sugars are added to foods in high concentration (at least 40% soluble solids), some of the water present becomes unavailable for microbial growth and the aw of the food is reduced.

6. CHEMICAL PRESERVATIES
To be in accord with good manufacturing practices, the use of preservatives :
Should not result in deception.
Should not adversely affect the nutritive value of the food.
Should not permit the growth of food-poisoning organisms while suppressing growth of the others that would make spoilage evident.

7. Chemical preservatives vegetables preservation are sulphur dioxide (SO2), benzoates, and sorbates.
The efficiency of chemical preservatives depends primarily on the concentration of the preservative, the composition of the food, and the type of organisms to be inhibited.

8. The concentration of preservative permitted by food regulations.
It is essential that the microbiological population of the food to be preserved is kept to a minimum by hygienic handling and processing.