Tartrazine, as mentioned above, is one of the colourings.  It colours food yellow, though when concentrated it is rather more orange (Figure 1).  It has the designation E102 in the classification and it is still licensed for use in food products in the UK1 and also in America2.  Despite this, it is hard to find any product with it as an ingredient.  As you may imagine, there are many other colourings.  This group is classified with the numbers E100-199.  Others of which you may have heard may include cochineal (E120), also known as carmine.  This is made from a crushed up beetle, dactylopius coccus, whose natural environment is in South
America.  It is believed to be this ingredient that makes the “red ones taste better” in a certain chocolate-based confectionery.  We can only imagine the horror suffered by ardent vegetarians when this beetle-based ingredient was made public knowledge.  Not surprisingly, it is not designated as ‘vegetarian friendly’ by the Vegetarian Society of The United Kingdom (VSUK)3.  The company that produces this particular confectionery has since discontinued the use of it, having replaced it with an Hibiscus extract, E163, referred to as anthocyanin.


Lycopene: A Case Study

Another red dye that is acceptable to the VSUK is E160.  This is a group of compounds related to vitamin A and includes lycopene (E160d).  When I first heard of it, I thought it was a stretchy elastic material worn by ardent runners, cyclists and people who do fitness videos – some sort of hideous combination of Lycra and neoprene.  Fortunately, it is a red colouring found in various plants that can also be used as a preservative.  Although it is found in a variety of vegetable sources, in practice tomatoes are the principle source for most humans.  A really potent source is the Gac fruit, though there are many others (Table).  Lycopene is also one of the carotenes.  As the name carotene suggests, it is related to derivatives of vitamin A (first found in carrots) and so has similar properties to them.  It is not necessary to understand the precise chemistry of lycopene to make sense of its uses, or understand why it does what it does.  However, if we examine the structure of the compound (Figure 2) we can see that there are obvious similarities between it and fatty acids (Figure 3).  Rancidity occurs when parts of the fatty acids (Figure 3) react with the oxygen in the air, which is what makes them go rancid.  Rancidity, by the by, is more to do with decaying flesh than has-been celebrities. 

So, in wanting to make foods containing fats last longer, we need to do something that will avoid fatty acids becoming rancid.  Lycopene ‘takes the hit’ instead of the fatty acids doing so; it reacts with the nearby oxygen instead of the fats.  This is rather like a left-wing tax system in which a richer person’s money is used to protect a poorer person’s, even though it has the same value.  However, unlike the traditional view of rich and poor, these two are as fat as one another.  The similarity in structures has a more general aspect, something that scientists call a physical property.  Not only do the two compounds behave in a certain way when exposed to the air (chemical property) but the structural similarity also means lycopene dissolves better in fatty foods than watery ones.  This ability to dissolve in one another is their similarity in physical properties.  Sadly the fact that vitamin A and similar things can dissolve in fats is not the tempting justification for eating fatty foods I had hoped for.


Is Colouring Worth the Hassle?

You may be wondering why we need to use colouring at all though.  After all, food has plenty of colour – all sorts of plants are green, many fruits are red and so on.  The problem comes with two main processes.

First, cooking.  Boiling carrots affects the colour.  This may seem a trivial problem at home; if you bought decent carrots and cooked them yourself, and under the dubious light of a dinner time/party, no one really notices.  The trouble is that for someone who wants to manufacture and sell this carrot, in a jar for example, they find it will be judged much more harshly than at a vegetable-infested soirée.  The consumer has not seen the glorious fresh carrots that went into making the mashed carrot.  Nor has he, or she, seen the delicate simmering in the pan.  They have also not seen the unidentifiable stain on the saucepan either, but that is still the first rule of catering service: ‘What the eye don’t see, the chef gets away with’.  Either way, as you may expect, the consumer will judge it only on what is in front of them.  If plain cooked carrot is put in a jar, in the supermarket this will fall short of what consumers expect from the fresh carrots they will have from fresh carrots two aisles away.

Second, is ageing of food.  Like humans, shrivelling, shortening,  wrinkling and varicose veins are all part and parcel of the ageing of food.  Well, not the varicose veins, but you could be forgiven for thinking that when you see the reduced sections of some supermarkets.  Either way, as a fruit passes senescence, i.e., the point at which it is at its most ripe, the compounds that give the fruit its colouring are destroyed chemically (broken down).  This can happen in a variety of ways.  For example, the group of compounds related to vitamin A can be broken down by light4 or by exposure to oxygen in the atmosphere5.  Food manufacturers therefore need to do something so that their food may be perceived as attractive-looking.  Sadly the normal methods of presentation used in advertising, i.e., putting a picture of a woman with her breasts half-showing on the front, are not quite enough.  The solution to this is two-fold.  First, they must prevent the degradation processes from happening (preserving, of which more below), and also add something to put the colour back in.  It is done with chemical colourings.  This immediately makes many people suspicious.  They feel cheated or even lied to, almost poisoned.  Though of course they have not been lied to really, assuming all the ingredients are listed on the packet.  What the manufacturer has done is provide what the customer wants – whether the customer is aware of these preferences and their obedience to them is less clear.  Why some customers want bright blue biscuits or green icing is a mystery to some, but when people are hungry, it is amazing what dross will sell.


Colour perception

It is possible to unlock this perception of colour versus flavour in a double-layered manner.  My demonstration on this when I am lecturing on the chemistry of food is to present four colourless-glass beakers with jelly in them.  One jelly is green, one is red, one orange and one blue.   I ask the audience which they think is the strawberry jelly.  If they have not spent too much time watching QI, they plump for the red one: strawberries are red and thus food containing strawberries is something we also expect to be red.  Perfectly sensible.  However, we revisit these four jellies when looking at flavouring.


1  ‘Current EU additives and their E numbers’, Food Standards Agency, 2010.

2  ‘Summary of Colour Additives for use in United States Foods, Drugs, Cosmetics and Medical Devices’, United States Food and Drug Administration, 2010.

3  ‘Fact Sheet: E numbers’, Vegetarian Society of the United Kingdom, 2011.

4  L. J. Whited, B. H. Hammond, K. W. Chapman, and K. J. Boor, J. Dairy Sci., 2002, 85, 351.