Colouring agents used in Pharmaceutical and Food Preparations

    Colouring agents are the substance which intended for promoting attraction and gives pleasant appearance to the pharmaceutical preparations.

    The pharmaceutical preparations are coloured dueto following reasons:-

i.        For identification of preparations: The pharmaceutical preparations are coloured in order to distinguish them from other preparations.

Example: Anaesthetic trichloroethylene is coloured blue in order to distinguish it from chlorodorm.

                  The medicated dressings and non-absorbable sutures are coloured order to distinguish them from simple surgical dressings and absorbable sutures.

ii.      To increase acceptability to patients: Generally, the patients have more attraction for bright coloured preparations.

Example: Coloured tonics and cherry red cough syrup for chlidrens.

        Skin coloured external preparations ( like ointments, creams, liniments and lotions) are more attractive to patients.

iii.    To giving warning: Some times colour is added in the preparation to give warning to the patients. ‘Not to take it orally’.

Example: Blue dye is added in methylated spirit so as to avoid its internal use.

iv.    To produce standard preparations: A suitable dye is used to give colour to the preparation containing more than one ingredient of different colours.

Example: Lactose is used as diluents for powdered opium, it is coloured with caramel to give a uniform appearance to the preparation.

Qualities of an Ideal Colouring agents

Following factors are generally to be considered while selecting any colorants.

1)      It should be readily soluble in water.

2)      It should have good colouring powder, so that only small quantity is required.

3)      It should be stable on storage and it should be unaffected by light, temperature and hydrolysis.

4)      It should be affected by oxidizing agents, reducing agents and pH changes.

5)      It should be free from objectionable odour and taste.

6)      It should have no physiological activity.

7)      It should be economical.

The amount of colorants generally added to liquid preparation ranges from 0.0005 to 0.1% depending upon the colorant and depth of colour intended. For powder 0.1% colorants is considered to be reasonable concentration.

Types of Colouring agents

1)      Natural colurings: These are obtained from mineral, plant, and animal sources.

a.   Mineral colours: Mineral colours frequently termed as pigments  Examples are red and yellow ferric oxides, titanium dioxide, carbon black, lead chromate, Prussian blue etc.

b.    Plant colours: Many plants contain colouring principles that may be extracted and used as colourants, e.g: chlorophyll. Anattenes are obtained from annatto seeds and give yellow to orange water soluble dyes. Natural beta carotene is a yellow colour extracted from carrots, alizarin is a reddish yellow dye obtained from the madder plant. The indigo plant is the source of a blue pigment called indigo. Flavones, such as riboflavin, rutin, hesperidin and quercetin are yellow pigments. Saffron is a glycoside that gives a yellow colour to drugs and foods. Most of these colorants possessing desirable qualities of stability, fastness and pleasant hue are now synthesized.

c.   Animal colours: Cochineal obtained from the insect coccus cacti contains principle the bright red colouring principle, carminic acid, a derivative of anthraquinone. Tyrian purple was prepared by air oxidation of a glandular secretion of snail, Murex brandaries. Animal colours are also not used now synthetic colorants are readily available.

2)      Synthetic colours: They can be obtained by chemical reactions. 

Table 1: List of Synthetic colours used in liquid dosage form

 

Colours	Common name	Colour index No.
Green         Yellow       Red           Blue     Orange   Brown   Black	Quinazarine green SS Alizarin cyanine green F Fast green FCF Green S   Tartrazine Sunset yellow FCF Quinoline yellow SS   Amaranth Erythrosine Eosin YS or Eosin G Toney red or Sudan III Fast red E   Indigo carmine Brilliant blue FCF   Orange G   Resorcin Brown   Naphthol blue black	61565 61570 42053 44090   19140 15985 47000   16185 45430 45380 26100 16045   73015 42090   16230   20170   20470

 

It is very difficulty to make a choice of colour to any preparation. The shade and the quantity to be incorporated is very important. Red colour in different shades is very much used in food products and pharmaceutical preparations. Tellow and green colour comes afterward. Blue and black colour are not appealing.

Colour and flavor are inter-linked with each other. If the flavor is that of lemon, the colour of the preparation should also be lemon (yellow) colour. If the flavor is that of rose then the colour of the preparation should be red.

The colours are also used in the form of lakes which consists of dyes absorbed generally on aluminium hydroxide. The lake consists of 15 to 40% adsorbed a