Food Preservatives
Preservatives: substances which when added to food retard, inhibit or arrest the activity of microorganisms.
q From prehistoric times humans have attempted to
preserve food products from the Decay effects of microorganisms. Some food
preservatives like salt, nitrites and Sulphite have been in use for many years.
q Even though newer packaging techniques, processing and
storage methods are able to preserve foods without chemical preservatives.
q Even today these chemicals play a significant role in
protecting the food supply mainly because preservation using chemical preservatives
is cheaper and more convenient.
Classification
of Food Preservatives
Preservatives are classified into two classes, Class I
and Class II preservatives.
1. Class I Preservatives
q Class I preservatives are also called as natural
preservatives. They are common salt, sugar, dextrose (glucose), spices, vinegar
or acetic acid, honey, and vegetable oils.
q There is no restriction to the addition of Class I
preservatives to any food.
2. Class II Preservatives
q Class II preservatives are also called as Synthetic or
Artificial preservatives. Use of more than one Class II preservative in a food
is prohibited unless specified under the Rules.
q The use of Class II preservatives is restricted to
only certain foods and the amount of the preservative which can be added to
these foods is also specified under the FSS Rules. The presence of a Class II
preservative in any food has to be declared on the packaging of the food.
q It includes Benzoic acid, sulphurous acids, nitrates
or nitrites, sorbic acid, potassium and calcium salts, calcium or sodium
propionates, lactic acid, sodium or calcium propionate, methyl or propyl
parahydroxy benzoic acid, sodium diacetate and sodium potassium and calcium
lactate and Nisin.
Salt
(sodium chloride):
q Salt has been used as a preservative since the
beginning of recorded history. Pickling of fruits and vegetables and salting of
fish and meat are widely practiced.
q The antimicrobial activity of sodium chloride is
essentially related to its ability to reduce water activity (aw) and create
unfavorable conditions for microbial growth. As the water activity of the
external medium is reduced, microbial cells are subjected to osmotic shock and
rapidly lose water through plasmolysis. These results in cells die or remain
dormant.
q
Other
possible mechanisms include limiting oxygen solubility in the medium and
toxicity of chloride ions.
q
The
inhibitory effect of sodium chloride is dependent on several factors
particularly pH. As acidity increases, less sodium chloride is required to
inhibit microbial growth.
q
Sodium
chloride intolerant bacteria are inhibited by concentrations as low as 1%. Some
bacteria like the lactic acid bacteria used in producing lactic fermented
vegetables can tolerate from 6–15 % sodium chloride.
q
In
general, food borne pathogenic bacteria are inhibited by a water activity of
0.92 or less which is equivalent to sodium chloride concentration of 13%. That’s
why for salt curing, sodium chloride concentration of about 13% is commonly
used.
Acetic acid:
q Synthetic vinegar (dilute acetic acid) and brewed
vinegar are widely used as acidulants and antimicrobials. Use of Vinegar in
pickles are common in our country.
q Acetic acid is more effective against yeasts and
bacteria than molds. Acetic acid is also more effective at lower pH. Generally,
1-2 % acetic acid is sufficient to inhibit most of the organisms.
Sugar and spices:
q The main function of sugar is to reduce the water
activity of the medium thus inhibiting the growth of microorganisms.
q Many chemical substances in spices (terpenes) have
been shown to have antimicrobial properties.
Class II Preservatives
Benzoic
acid and benzoates:
q Benzoic acid is found naturally in cranberries, plums,
prunes, cinnamon, cloves and most berries. It is a strong antimycotic agent.
Most yeasts and molds can be controlled using 0.05–0.1% benzoic acid. Control
of many bacteria requires much higher concentration.
q Benzoates are most effective at low pH (pH 2.5–4.0).
Benzoic acid is permitted in several products like squashes, syrups, crushes,
fruit juices, jams, jellies, marmalade, beverages, pickles and tomato products.
Benzoic acid and its sodium and potassium salts have been generally recognized
as safe (GRAS).
Sulphur
dioxide and Sulphites:
q Sulphur dioxide and its various salts have a long
history of use dating back to the times of the ancient Greeks. They have been
used extensively as antimicrobials and to prevent enzymatic and non-enzymatic
browning in a variety of food products.
q Sulphur dioxide is a colorless, nonflammable gas with
a suffocating odor. It dissolves readily in water to produce sulphurous acid
(H2SO3). Sulphur dioxide and sulphites are permitted for a number of products
like fruit pulps, squashes, syrups, crushes, cordials, wines, RTS beverages,
and dehydrated fruits and vegetables.
q Sulphur dioxide is also used as an anti-browning
agent. Fruits are exposed to fumes of burning Sulphur before drying to prevent
browning and also insect and microbial attack. Sulphite solutions are also used
as dip solution for vegetables before drying or dehydration.
q Sulphur dioxide and several sulphites have GRAS
status. Sulphites cannot be used in meats and in foods that are sources of the
vitamin thiamine. As sulphites have strong bleaching action on plant pigments
like anthocyanins, they should not be used for preserving such products.
Sorbic
acid and sorbates:
q Sorbic acid and its sodium, potassium and calcium
salts are collectively known as sorbates. Sorbic acid is present in some
berries like berries of the mountain ash berry (rowanberry). Sorbates inhibit
most of the species of yeasts and molds. Several species of bacteria are also
inhibited by sorbates.
q Sorbates are permitted for only a few fruit and
vegetable products. They include jams, jellies, marmalades, glazed or candied
fruits, fruit bars, fruit juice concentrates and prunes. Some of the other
products include cheese, flour confectionary, smoked fish, preserved chapattis
and fat spreads. Sorbic acid and potassium sorbate have GRAS status.
q Nitrites have been used in meat curing for many
centuries. For meat curing, nitrite is used along with a mixture of salt,
sugar, spices, and ascorbate. Nitrite contributes to the development of the
characteristic color, flavor, and texture improvement and preservative effects.
q Nitrites are white or pale-yellow hygroscopic
crystals. Sodium nitrite is quite soluble in water. Nitrite has a strong
inhibitory action against Clostridium botulinum and several other
microorganisms. It is more effective below neutral pH (below 7.0).
Antibiotics:
Biologically derived antimicrobials:
These substances are allowed for food use only in recent years. Nisin and Natamycin have been permitted in some foods.
Nisin
q It is a
polypeptide produced by Steptrococcus lactis (now called lactococcus
lactis). Nisin has a narrow spectrum affecting only gram-positive bacteria,
and it generally does not inhibit gram-negative bacteria, yeasts or moulds.
q The antimicrobial
action of nisin is pH dependent, it increases as the pH decreases. It is
effective at very low concentrations i.e. 0.04-2.0 ppm. Nisin has been
permitted in packaged coconut water and canned rasagolla.
Natamycin:
q It is produced by
the bacterium Streptomyces natalensis. Natamycin is primarily effective
against yeast and moulds and is ineffective against bacteria, viruses and
actinomyces. Natamycin is also effective at very low concentrations i.e. 5-10
ppm. Natamycin has been permitted for surface treatment of hard cheese
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