FOOD PRESERVATION BY SALT, ACID, SUGAR AND CHEMICAL PRESERVATION

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.

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 (a w ) of the substrate, thus controlling microbial growth by a method independent of its toxic effects.

• 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.

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 a w of the food is reduced.

CHEMICAL PRESERVATIES

To be in accord with good manufacturing practices, the use of preservatives : 1. Should not result in deception.

2. Should not adversely affect the nutritive value of the food.

3. Should not permit the growth of food-poisoning organisms while suppressing growth of the others that would make spoilage evident .

• Chemical preservatives vegetables preservation are sulphur dioxide (SO 2 ), 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.

• 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.