CHEMICAL PRESERVATIVES:

CHEMICAL PRESERVATIVES:

The food additives which are specifically added to prevent the deterioration or decomposition of food have been referred to as chemical preservatives.

Preservatives may inhibit microorganisms by interfering with their cell membrane, their enzyme activity or their genetic mechanisms.

Factors that influence the effectiveness of chemical preservatives:

·     Concentration of a chemical

·     Temperature

·     Time

·     Kind, number, the age of organisms

·     Chemical and physical characteristics of the substrate (moisture, pH, kind and amount of solute etc.)

Ideal antimicrobial preservative:

·     Non-toxic to human beings or animals.

·     Have a wide range of antimicrobial activity

·     Not effect flavor, taste or aroma of food

·     Not encourage the development of resistant strains

·     Economical

·     Kill rather than inhibit microorganisms

·     Should not be inactivated by food

SUGAR AND SALT:

·     these compounds lower the water activity (aw)

·     NaCl is used in brine and curing solution.

·     Salts have the following effects:

·     Causes high osmotic pressure and hence plasmolysis of cells.

·     Reduces solubility of oxygen in moisture.

·     Interfere with the action of proteolytic enzymes.

·     Ionizes to yield Cl ion ( oxidizing agent)

·     Dehydrates food by drawing out moisture hence, dehydrates microbial cells.

·     Sugars (glucose or sucrose) make water unavailable to the organism by the osmotic effect.

·     E.g.., sweet condensed milk, jellies, fruits

ORGANIC ACID AND THEIR SALTS:

·     They are added to foods by fermentation.

·     Lactic, acetic, propionic and citric acids or their salts may be added to foods or developed in foods by fermentation.

·     Citric acid is used in syrups, drinks, jams, and jellies as a substitute for fruit flavors and for preservation.

·     Lactic and acetic acids are added to brines of various kinds, green olives etc.

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·     (A)  benzoic acid and parabens

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·     Sodium benzoate was the first chemical preservative approved by FDA.

·     Mainly inhibitory against yeasts and molds

·     The antimicrobial activity of benzoate is related to pH, greater at low pH (2.5-4) and essentially ineffective at neutral pH.

·     Undissociated acid is an effective agent.

·     It is corporate into jams, jellies, beverage, salads, pickles, fruit juices etc.

·     Two esters of p-hydroxybenzoic acid, methyl paraben, propyl paraben are extensively used in foods

·     Similar to benzoic acid but can be effective at higher pH because of the esterification of carboxyl group.

·     More effective in molds than yeasts.

·     Mode of action: the undissociated form is soluble in the cell membrane and act apparently as proton ionophores. They facilitate proton leakage into cells and thereby increase the energy output of cells to maintain their usual internal pH. With the disruption of membrane activity, amino acid transport is adversely affected.

·     It blocks the oxidation of glucose and pyruvate at acetate level. Inhibit germination of outgrowth during endospore germination.

CITRIC ACID:

·     Found in citrus fruits.

·     Widely used in carbonated beverages and as an acidifying agent of foods because of its unique flavor properties.

·     Highly soluble in water, unlimited acceptable intake

·     Less effective than other acids.

·     Used in Fruit juices, and jams.

ETHYLENE OXIDE:

·     Acts as a sterilant. Kills all microorganisms

·     Acts as strong alkylating agents attacking labile hydrogen.

·     The H atom attaches itself to oxygen, forming hydroxyl ethyl radical, CH2CH2OH.

·     This radical blocks reactive groups within microbial proteins, resulting in inhibition.

·     Ethylene and Propylene oxide: used as sterilants for packaging materials, fumigation of warehouses. 'cold sterilization’ of numerous plastics, chemicals, pharmaceuticals, syringes, and hospital supplies.

·     Use of ethylene oxide is restricted to spices and other processed natural seasonings.

NITRATE AND NITRITES:

·     combination of these salts used in curing solution and curing mixture for meats.

·     Curing is a food preservative and flavoring process with the aim of drawing moisture out of food by the process of osmosis.

·     Nitrites decompose to nitric acid which forms nitrosomyoglobin when reacts with pigments in meats i.e., myoglobin in reducing condition and thereby forms a stable red color.

·     Nitrites react with secondary and tertiary amines to form nitrosamines, which are carcinogenic.

·     Inhibits Clostridium botulinum in meat products along with Staphylococcus aureus and Bacillus sp.

·     Inhibits Clostridium botulinum by interfering with Fe-S enzymes such as ferredoxin and thus preventing the synthesis of ATP from pyruvate.

·     Nitrous oxide is a powerful reducing agent causing disruption of cell metabolism and inhibiting germination and outgrowth of endospores.

·     Nisin (bacteriocin) can be used along with nitrites.

·     Nitrite levels of 100 ppm in presence of NaCl (3-5%) is sufficient to impart adequate flavors, color, anti- botulism activities.