Definition of artificial or synthetic dye:

A dye may be defined as an organic compound containing both chromophore and auxochrome linked to a benzene ring. Chromophore imparts the compound colour. A compound may be coloured but it will not be declared as dye unless it can unite with the fibre or fissues e.g. m-dinitrobenzene, dimethylinitrosamine etc. are coloured compound but not dye.

Auxochromes - -OH, -NH2 etc.

To be a dye it must contain a group that imparts the compound the properties of electrolytic dissociation i.e. it will have the power of salt formation. Such groups are known as auxochromes, Chromophoras – nitro (-NO2) nitrose (-NO), AZO (-N=N-), etc.

Dyes may be acidic and basic. A dye which ionises as negative radical is known as acidic (anionic) dye and which ionises as positive charge known as basic (Cationic) dye e.g. Rhodamine B. But all the dyes are not safe for food use. Weyl and Liebor in 1892 first pointed out some poisonous character of dyes. Some of the toxic properties of comonly used dyes are given below: -

1. Metanil yellow (widely used in foods in India, marketed name "Kishori") produces testicular degeneration in experimental animals and also damages chromosomes.
2. Butter Yellow, Rhodamine B, Auramine, Blue VRS are reported to be carcinogenic.
3. There was ulceration and abacess formation at the site of injection in rats with Blue VRS.
4. After the administration of Congored, leison develop in the brain, kidney and eyes of rat, Malachite green increases the incidence of lung, breast, ovary and liver tumour.
5. Long-term administration of yellow OB and yellow AB at different levels in the diet has been reported to cause varying degrees of degenerative changes in rat test is. Again long-term toxicity test of some dyes like Sunset yellow. Erythrosine, Violet 6B on various animals were proved to be non-toxic thus we can see many dyes have some toxic effects and some do not.

For declaring safe for using in foods the dyes must satisfy the following criteria: -

1. It must be nontoxic and water-soluble. If it is not water soluble then there is every possibility of depositing dyes in the body which may create danger after wards.
2. Azo dyes to be used as food colour should preferably contain sulphonic groups in both the diazonium and coupling components.

If they are made from a diazonium or a coupling component not containing a sulphonic group, then one of the reduction products formed in the body will therefore be an unsulfonated aromatic amine which is not readily eliminated because of its solubility in fat and this may create health hazard. Some-amines are also known to be carcinogenic.

3. Food dyes must be acidic in nature as because basic dyes may react with the nucleic acid of the body.

Thus it can be observed that all dyes cannot be used in foods. Here comes the necessity of food laws.

In our food laws only eight dyes are allowed to be used in foods. Again there is also restriction of using natural colours in foods. All the natural colours cannot be used, as there is very limited reports on toxicity of most of the natural colours.

List of Permitted Natural Colours:

i)b - Carotene

ii)b - Apo-8’ - carotenal

iii)Methyl ester of b -apo-8" Carotenoic acid.

iv)Ethyl ester of b -apo-8" Carotenoic acid.

v)Canthaxanthin

vi)Chlorophyll

vii)Riboflavin

viii)Caramel

ix)Annatto

x)Ratanjot

xi)Saffron

xii)Curcumin or turmeric

 List of permitted synthetic Dyes:

These dyes can be used in a some particular food items and the amount of dye to be used in food is also restricted. The maximum amount of dyes can be used in food is 0.1 gms per kilogram of the foods. The following are the food items where these colours can be used.

a) Ice cream including mixed Ice cream
b) Dairy products except milk, dahi, butter, ghee, cheese, chhana, condensed milk, cream, skimmed milk, butter milk, toned milk, doubled toned milk, recombined milk, skimmed milk chhana, standardised milk chhana, Khoa, dry whole milk, dry skimmed milk and baby food.
c) Smoked fish
d) Egg preparations
e) Biscuits pastry, confectionery, savouries like dal moth, Mongra, Phul Gulab Papper, sago or plain dal bhaji, wafer and similar products and sweets.
f) Fruit products (except as otherwise provided in Appendix B)
g) Non-alcoholic beverages except tea, cocoa malted foods and coffee.
h) Custard powder
i) Jelly crystals
J) Soup powder
k) Processed or preserved vegetables
l) Flavouring agents
m) Ice candy

Besides this the colours should be pure and free from any harmful impurities.

Due to bad practice or ignorance some non-permitted synthetic dyes are used indiscriminately. This poses a problem in identification of dyes in foods. Various identification methods were developed in the laboratory, generally one adopt paper chromatography for detection after wool dyeing. The wool is protein in nature and in acidic conditions following reaction occurs between wool and the acid dye.

+ _ _ +

Dye So3 H3 N…. Co H2 Dye So3 H3 N

---------- + ---------------- + = ------------------ + --- Co2 H

Dye Wool Dyedwool

This dyes wool when treated with alkali it then liberates the dye. This is in short theory of wool dyeing. Finally dye is identified by paper chromatography.

Recently gel-electrophorisis emthods has been developed which is very accurate and less time consuming.

Commonly found non-permitted dyes in foods are metanil yellow, Orange II, Rhodamine B, Auramine and Blue VRS. Most of sweets like Bondi are coloured with metanil yellow and the red coloured syrups with Rhodamine B.