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Colour in Food
We need colour in food because all of the senses contribute to the experience of eating.
The impression food makes on us is a melange of sensations, and colour and surface appearance are amongst the most important. There is nothing dubious about this. Many of the great experiences in life involve a mix of sensations, and eating is one of the original multimedia experiences. In some cuisines, colour has played a more important part than others, Indian food for example with its saffron-coloured rice and the lurid red of tandoori chicken. Often we associate such colours with strong flavors when in fact what gives the colour and the flavour are entirely distinct.
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Colours of our Food
There are three main classes of colour in foods: natural colours, browning colours, which are produced during cooking and processing, and additives. The principal natural colours, most of which, in refined form, are used as additives, are the green pigment chlorophyll, the carotenoids, which give yellow to red colours, and the flavonoids, with their principal subclass the anthocyanins, which give flowers and fruits their red to blue colours.
There has been much interest in carotenoids in recent years, especially beta-carotene. Besides being a natural orange pigment (carrots, mango, papaya, winter squash, etc) it is converted in the body to vitamin A and has antioxidant powers. It is believed to have a beneficial effect in reducing the risk of some cancers and perhaps heart disease.• Feeling blue - feeling sad or depressed
Increasingly, food additive colours are based on anthocyanins derived from sources such as red grapes or beet but the first additive colours were the synthetic dyes. Chemical dyes have stronger colours than natural colouring agents such as cochineal. Many of these dyes were originally derived from coal-tar, and were commonly called 'coal-tar dyes'. The term is still sometimes used although the dyes are no longer made from this source. Chemically, the dyes are azo dyes, that is they contain the azo group, which confers bright colours which vary in hue depending on the rest of the molecule. Colour chemicals are by definition active chemicals and hence require greater care than bland additives such as emulsifiers. In 1937 the dye butter yellow (dimethylazobenzene) was found to cause cancer in rats. The other azo dyes became suspects and one by one they have been weeded out of the list of acceptable additives.
The main trend in colour in food is towards the use of anthocyanin colours 2. No doubt 'anthocyanin' will become another additives bogey word for some people, but it should be remembered that anthocyanins are the principle type of pigment employed by nature in flowers and fruits. At present they are mainly consumed in foods which naturally contain them, especially red wine, for instance, but they will increasingly be consumed as additives which have been extracted from one plant source and used to colour totally different foods. There is some evidence that anthocyanins have beneficial health properties. They have antioxidant properties for example and contribute to the positive health effects of red wine which counteract the negative effects of alcohol itself.
Some sources of anthocyanins, besides red grapes, are elderberries, red cabbage, blood orange, the less familiar black chokeberry, and the sweet potato. Anthocyanins are highly dependent on acidity and lose their colour in conditions of low acidity. The development of anthocyanins which are more stable across a range of acidities is likely. There has been much recent activity in the field of red anthocyanin pigments with red potatoes, beet and amaranth 3 (a relative of the beet family) to the fore. |
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Natural Colours in Food
Colour is one of the greatest life enhancers we have. The challenge for chemist is to devise colours that are safe to use in food. It isn't enough to say: use natural colours. Natural colours are also chemical pigments. Many foods are unlikely to reach supermarket shelves with their natural colour at its peak. The most notorious examples are canned foods, such as peas and strawberries, which would be khaki and dull brown, respectively, without added colour.
More subtly, consumers associate certain foods with a certain hue, preferring richer yellow butter and egg yolks, so butter and egg-yolk colour are sometimes enhanced. Recently, a supermarket chain banned the use of canthaxanthin (E161g) from its eggs. Canthaxanthin is a nature-identical yellow pigment, a carotenoid, which is sometimes added to the feed of hens. Since canthaxanthin is the pigment nature uses when she wants a yellow colour its addition in this way is not such a drastic step.
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