CHEMICALS OF DISTINCTION

The chemistry of life depends on the amazing ability of the carbon atom to combine with itself to form large structures in every conceivable combination. This is DNA with its double helical structure. All the vital molecules of life have structures just as precise. This requires that nutrition also should be a precise science.

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HOW NUTRITION WORKS

To be nutritious food ingredients have to have a specific function.

WHY INGREDIENTS WORK

How the cook uses a battery of chemical reagents (better known by their more homely names) to create familiar foods

CHEMIST IN THE KITCHEN

Chemicals have always been welcome in the kitchen: sodium bicarbonate, pectin, yeast, acetic acid etc.

One problem in understanding the chemical basis of food (and of life itself) is that what we know of it contradicts our subjective notions. Words associated with nature suggest simplicity, wholeness, purity, whereas the word chemistry suggests complexity, atomisation, pollution. In fact, chemistry began with great simplicity, trying to understand what were the irreducibly pure elements in existence, hydrogen, oxygen, carbon etc. When chemicals from living things were analysed, and it was a long time before this was achieved, they were found to be of bewildering complexity. Many chemists have devoted their life's work to understanding the structure of a single molecule of life, such as Dorothy Crowfoot Hodgkin, working on Vitamin B12, or Frederick Sanger on Insulin, so complicated are such structures.

Purity is not nature's strong point. Many of its apparently simple substances, such as milk for example, contains hundred of chemicals balanced in a very delicate physical condition. Milk itself is a very complex emulsion of highly dispersed, very tiny, fat particles suspended in a watery solution. Dissolved in the fatty phase are some vitamins, phospholipids, carotenoids and cholesterol; the watery (aqueous) phase contains proteins, mineral salts, milk sugar (lactose) and water-soluble vitamins.

The key to food chemistry is that scientists have discovered that out of the thousands of chemicals in living cells, some have very specific functions. Now, these active chemicals are often synthesized and used instead of or alongside natural components. Citric acid, for example, used to be extracted from lemons but is now usually made by microbiological fermentation. It is a very simple substance and is exactly the same whatever its source.

Vanilla used to be a rare, expensive and exotic flavour extracted from the vanilla orchid, found in South America. The flavour is due almost entirely to a single chemical, vanillin, which was synthesized as early as 1874. So successful was the introduction of synthetic vanilla that 'vanilla' is now a byword for the bland and ordinary instead of the exotic and rare. Sometimes, once the class of an active compound is recognised, similar but chemically distinct molecules are developed which fulfill the same function but which may have enhanced properties.

This principle, of the relation between natural products and chemical additives, holds across all categories of food additives. Particular chemical structures have particular properties, whether as anti-oxidizing agents, emulsifiers, or flavourings, and nature and chemist alike explore these properties in a variety of chemicals which have subtly different effects. The categories of additives are families of active ingredients in which a continuum is seen between the chemicals of natural origin and those of purely synthetic derivation.

Chemicals, in the context of living systems, are either bland or highly active. It is this we should be concerned with in assessing additives. Many natural chemicals, such as the active principle of chili peppers, capsaicin, or the sulphur compounds that give onions their pungency, are highly active (active of course doesn't necessarily mean dangerous: onions are highly beneficial). Many additives, however are bland: they are intended to fine-tune the properties of food, and the tolerance of food systems to extremes is low. Such chemical additives as sodium carboxymethylcellulose are very similar to the chemicals living systems use and are equally bland. This is particularly the case with additives that mediate the physical properties of food such as the emulsifiers.