Colorants are used to make the food more acceptable to the consumer, but since many adverse reactions to artificial colorants have been reported, many of these have been banned in some countries and natural colorants are being used more frequently. In the UK some foods are not permitted to contain added colorants, namely raw meat, game, poultry, fish, fruit or vegetables, tea, coffee, condensed or dried milk, cream and certain types of bread. Bread, cheese and butter may contain a restricted number of dyes, and raw meat may be coloured with the basic dye methyl violet. Allergic reactions or intolerant responses have been reported for most of azo dyes used as food colorants, and in some countries (Norway) they have been banned. In other countries, including Sweden, Finland, Austria, Greece and Japan, their use has been severely restricted. Nevertheless, azo dyes are still used extensively throughout the world in spite of the reported health hazards.
Some of the more common azo colours include amaranth (red), azorbin (red), brilliant black, sunset yellow (yellow), carmousine and tartrazine (yellow), most of which are potential allergens as demonstrated in their potential to induce histamine release by leukocytes of normal and urticaria patients.31 A similar, though reduced potential, was also demonstrated for non-azo colours such as quinoline yellow, green S and indigo carmine. Colorants have been shown to induce asthma, rashes, hay fever, blurred vision and tummy upsets. Moreover their role in inducing hyperactivity and other behavioural disorders in children has been clearly established. In one study, a group of children on an additive-free diet, were given a
cookie containing a blend of eight food colours. Within three hours after the ingestion of the cookie some of the children showed impaired perceptual-motor performance and increased hyperactive behaviour with the greatest effect being on the youngest individuals.33,34 Impaired learning ability is another negative response to colorants, and some children develop a short attention span, whine and tend to throw tantrums.33
Azo compounds have also been reported to effect aggregation of platelets, and to have an inhibitory effect on both prostaglandin synthetase and thromboxane activity, though these claims have been challenged. Tartrazine in particular has been implicated in cases of acute urticaria angio-oedema, eczema, asthma, nausea and migraine attacks by impacting on the immune system.35,36 Some of the caramels, particularly ammonia caramel, have been shown to have lymphocyte depressing effects, and the orange/red colorant canthaxanthin, which is used to obtain artificial browning, has been found to produce crystalline deposits on the retina. Another red colorant, erythrosine, has been shown to affect thyroid function and may have oncogenic and carcinogenic effects. Concern about these issues has prompted a reduction of the ADI and NEL (no effect level) for most of these compounds.37 In the USA the colorant amaranth and ponceau 4R (red) are also banned.
Natural food colours are becoming increasingly popular, and the main classes are the carotenoids, beetroot extract, anthocyanins, riboflavins, cochineal, chlorophylls and naturally coloured foods such as paprika, turmeric, saffron, and sandalwood together with extracts of these materials. Though sensitivity to natural colorants is considerably lower than artificial colorants, in some cases they may also elicit a negative response. Overall it can thus be said that avoidance of food colorants can only be of advantage to the consumer.