Food Additives

The intentional addition of substances to food is not a recent practice, as might be supposed. For centuries salt has been commonly used as a preservative and spices to flavour, and perhaps disguise, poor-quality food. In Ancient Rome sapa was used to sweeten food and wine, and the ancient Greeks also added it to wine. It eventually became associated with adverse effects, such as constipation, tiredness, colic, infertility, and anaemia.

What was in the sapa that caused these effects? We have come across these symptoms before but in a different context. The sweetening agent sapa was made by boiling grape juice or wine, often after it had started to turn to vinegar. The boiling was done ideally in lead pots, most of the liquid evaporating to produce a syrupy solution. In describing the process, the Roman writer Pliny (ad 23-79) said that the use of a lead pot was essential for good sapa. In grape juice or wine there are acids like tartaric acid and citric acid, and in vinegar the alcohol in the wine has been turned into acetic acid by bacteria. When the grape juice was boiled in lead pots, these acids reacted with the lead-producing salts, for example lead acetate, which were soluble in water. The lead acetate was very sweet—it was called 'sugar of lead' in later times when its deadly composition was known. The concentrated solution, or the crystals that formed from it, were used to sweeten food and wine. It also preserved wine as the lead inhibited the growth of any bacteria or fungus. As recently as the nineteenth century lead shot was added to bottles of port for this reason.

The use of sapa became associated with adverse effects on health, and it became known that wine to which it had been added would induce abortions, for example. For this reason prostitutes used it and at the same time acquired a pale complexion as a result of anaemia caused by the lead. Pliny knew of the adverse effects of wines to which sapa had been added, writing that 'from the excessive use of such wines arise dangling paralytic hands', no doubt a reference to the effects of lead on the nerves (see p. 142). Dioscorides, a Greek physician writing before Pliny, stated with prescience that 'wines so treated are most hurtful to the nerves'.

While the use of 'sugar of lead' as a sweetener died out after the fall of the Roman Empire, the use of lead salts in food did not. Much more recently, for example, lead chromate, or 'chrome yellow', has been used to colour sweets and custard powder. As recently as the nineteenth century toxic metal salts were used as food colourants, for example the dye Scheele's green was used to colour blancmanges green. This dye is copper arsenite, containing both copper and, more importantly, arsenic.

Early in the twentieth century a very hazardous chemical was used as a food colourant: 4-dimethylaminoazobenzene, so-called 'butter yellow', was a yellow azo dye used in some countries to colour butter, before extensive testing was required. When it was studied in 1947, the dye was shown to be a potent carcinogen capable of causing liver tumours in experimental animals, and it was rapidly withdrawn. Fortunately, the treatment of food with additives, which has now become more extensive, is now safe.

Substances that are intentionally added to food and do not contain any nutritional value are termed food additives. These are added to, or used in the preparation of, food as preservatives or to change its texture, consistency, taste, colour, alkalinity, or acidity. There are several types of food additives, details of which are given below. In Europe food additives are given an E number1 (see Table 8 for examples), while different code numbers are used in the USA. These numbers appear on the packaging. It has been estimated that there are well over 3,000 different additives, most of which are used purely for cosmetic purposes, and relatively few of which are employed as preservatives or in processing.

Almost all of us are exposed to these additives. A cursory look around my kitchen revealed:

orange squash, containing beta carotene (colour);

cola drink, containing caramel (colour), aspartame and acesulfame

(sweeteners), and sodium benzoate (preservative); tonic water, containing saccharin and aspartame (sweeteners), as well as quinine (flavour); a packet of soup, containing caramel (colour); a jar of pickle, containing caramel (colour);

glacé cherries, containing erythrosine (colour) and potassium sorbate and sulphur dioxide (preservative); custard powder, containing annatto (colour); and a packet of prawn crackers, which while it boldly claimed to contain 'no artificial preservatives or colouring agents' admitted the addition of monosodium glutamate (flavour enhancer).

On venturing into the bathroom and inside the medicine cabinet, I discovered to my surprise a cold cure containing sunset yellow (colour). However, pride of place in the list of additive-laden products went to the vitamin pills which contained the following:

colourants: titanium dioxide, iron oxide; anticaking agents: magnesium stearate, silicon dioxide; sweeteners: aspartame, acesulfame K glazing agents: shellac, carnauba wax;

stabilizers: sodium carboxymethyl cellulose, acetylated monoglyceride; tableting aid: polyvinyl pyrrolidone; and the vitamins, of course!

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