This document discusses food preservatives. It explains that preservatives are added to foods to reduce spoilage from microorganisms and prevent food-borne infections. Preservatives work by interfering with microbial cell functions or reducing the pH to prevent microbial growth. Chemical preservatives specifically target microbes and are categorized into class I (e.g. salt, sugar) and class II (e.g. benzoic acid, sulfur dioxide). Common preservatives like salt, sugar, vinegar, and sulfur dioxide are described along with their antimicrobial mechanisms.

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.

9. 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.

10. 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.

11. 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

12. 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

13. 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.

14. 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.

15. 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.