Preservation by chemicals

FOOD SCIENCE

1. PRESERVATION BY CHEMICALS

2. PRESERVATIVE A preservative is a substance or a chemical that is added to products such as food, beverages, pharmaceutical drugs , paints , biological samples , etc.. Preservative food additives reduce the risk of food borne infections , decrease microbial spoilage , and preserve fresh attributes and nutritional quality.

3. PRESERVATION PRINCIPLE Food preservatives interfere with the mechanism of cell division, permeability of cell membrane and activity of enzymes and inhibit the spoilage factors. These work either as direct microbial poisons or by reducing the ph to a level of acidity that prevents the growth of microorganisms.

4. FOOD PRESERVATION

5. USE OF CHEMICAL PRESERVATIVES Chemical preservatives are food additives, which are specifically added to prevent the decomposition of food. These are factors causing spoilage. The chemicals are effected by interfering with cell membrane of the microorganism, their enzyme activity and genetic mechanism; and by acting as antioxidants.

6. CLASSES OF PRESERVATIVES Chemical preservatives may be grouped into two classes. 1. Class I preservatives. 2. Class II preservatives.

7. CLASS I PRESERVATIVES The first one includes the use of sugar, salt, spices, acetic acid(vinegar) and alcohol, and is referred to as class I preservatives and is considered to be relatively safe to humans. Sugars and salt in high concentrations have high osmotic pressure and draw water from microbial cells or prevent normal diffusion of water into these cells resulting in a preservative condition.

8. PRESERVATION BY SALT Salt acts as preservative when its concentration is increased above 12 %. Salt levels of about 18 to 25% solution will generally prevent all growth of microorganisms in foods.

9. PRESERVATION BY SUGAR Sugar in high concentrations acts as a preservative due to osmosis. Sugars attracts all available water and water is transferred from the microorganisms into the concentrated sugar syrup.

10. CLASS II PRESERVATIVES The second group includes the use of benzoic acid, sulfur dioxide, nitrates and nitrites and a variety of neutralizers, firming agents and bleaching agents and referred to as class II preservatives

11. SULPHUR DIOXIDE AND SULPHITES Sulphur dioxide and its derivatives have been widely used in foods as a food preservative. It serves both as an antioxidant and reducing agent. Sulphur dioxide gas (SO2) is one of the oldest known fumigant and a wine preservative. Sulphites are effective in producing more SO2 ions at ph values less than 4.0. Sulphites inhibit microbial growth by reacting with the energy rich compounds like adenosine tri phosphate

12. BENZOIC ACID AND RELATED COMPOUNDS It was the first chemical preservative permitted in foods by the FDA, and it continues to be widely used in large number of foods. It is used in acidic foods, these act essentially as a mould and yeast inhibitor. It is more effective against yeasts than against moulds. Sodium benzoate, sodium salt of benzoic acid, is very effective as it is nearly 180 times more soluble in water than benzoic acid when dissolved in water.

13. SORBIC ACID AND RELATED COMPOUNDS Sorbic acid and related compounds have antimicrobial properties they are available as sorbic acid , potassium sorbate , sodium sorbate or calcium sorbate .

14. ANTIOXIDANTS The oxidation process spoils most food , especially those with a high fat content. Fats quickly turn rancid when exposed to oxygen . Antioxidant prevent or inhibit the oxidation process.