SPICEBOX OF COLOURS
The colours of food are richly evocative and inextricably blended with flavour,
texture, and cultutral associations of food. Many colours are noew derived from plant
pigments such as the anthocyanins of red grapes.
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ACIDS
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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.
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.1
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. When
synthetic dyes were discovered (mauve was the first, discovered in 1856 by the English
chemist William Perkin) they were initially used in textiles, but by 1900 eighty chemical
dyes were used in food in the USA. 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.
Today a limited range of azo dyes is used in food. All have been extensively tested. So
long as they are fully tested, there is no excuse for the puritanical attitude that adding
colours to food is wrong. Why did we add colour to the television, the newspapers and to
our computers? 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.
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.
1J. Bland, 'The beta-carotene controversy in perspective', Journal of
Applied Nutrition, Vol 48, pp42-45, 1996
2 P.Bridle and C. F. Timberlake, 'Anthocyanins as natural food colours - selected
aspects', Food Chemistry, Vol 58, No 1-2, pp 103-9, 1997
3 Y. Cai and H. Corke, 'Amaranth Betacyanin Pigments Applied in Model Food
Systems', Journal of Food Science, Vol. 64, No 5, 1999, pp 869-873. |
