Introduction

For the chemists of the 18th and 19th centuries an understanding of the chemical nature of our food was a major objective. They realised that this knowledge was essential if dietary standards, and with them health and prosperity, were to improve. Inevitably it was the food components present in large amounts, the carbohydrates, fats, and proteins, that were first nutrients to be described in chemical terms. However, it was also widely recognised that much of the food, and drink, on sale to the general public was very likely to have been adulterated. The chemists of the day took the blame for some of this:

There is in this city [London] a certain fraternity of chemical operators who work underground in holes, caverns and dark retirements ... They can squeeze Bordeaux from the sloe and draw champagne from an apple.

The Tattler, 1710

but by the middle of the 19th century the chemists were deeply involved in exposing the malpractices of food suppliers. Chemistry was brought to bear on the detection of dangerous colourings in confectionery, additional water in milk, beer, wines and spirits, and other many other unexpected food ingredients. A major incentive for the development of chemical analysis was financial. The British government's activities were largely funded by excise duties on alcohol and tea and large numbers of chemists were employed to protect this revenue.

As physiologists and physicians began to relate their findings to the chemical knowledge of foodstuffs the need for reliable analytical techniques increased. 20th century laboratory techniques were essential for the study of vitamins and the other components that occur in similarly small amounts, the natural, and artificial colour and flavour compounds.

Until the use of gas chromatography (GC) became widespread in the 1960s the classical techniques of 'wet chemistry' were the rule but since that time increasingly sophisticated instrumental techniques have taken over. The latest methods are often now so sensitive that many food components can now detected and quantified at such low levels (parts per billion, 1 microgram per kilogram, are commonplace) that one can have serious doubts over whether the presence of a particular pesticide residue, environmental toxin or the like at the detection limits of the analysis really has any biological or health significance. It is perhaps some consolation for the older generation of food chemists that some of the methods of proximate analysis* that they, like the author, struggled with in the 1960s, are still in use today, albeit in automated apparatus rather than using extravagant examples of the glassblower's art.

By the time of World War II it appeared that most of the questions being asked of food chemists by nutritionists, agriculturalists, and others had been answered. This was certainly true as far as questions of the 'what is this substance and how much is there?' variety were concerned. However, as reflected in this book, over the past few decades new questions have been asked and many answers are still awaited. Apart from the question of undesirable components, both natural and man-made food chemists nowadays are required to explain the behaviour of food components. What happens when food is processed, stored, cooked, chewed, digested and absorbed? Much of the stimulus to this type of enquiry has come from the food-manufacturing industry. For example, the observation that the starch in a dessert product provides a certain amount of energy has been overtaken in importance by the need to know which type of starch will give just the right degree of thickening and what is the molecular basis for the differences between one starch and another. Furthermore that dessert product must have a long shelf-life and look as pretty as the one served in the expensive restaurant.

In recent years these apparently rather superficial aspects of food supply have begun to take on a wider significance. The nutritionists, physiologists and other scientists now recognise what consumers have always known – there is more to the business of feeding people than compiling a list of nutrients in the correct proportions. This is as true if one is engaged in famine relief as it is in a five-star restaurant. To satisfy a nutritional need a foodstuff must be acceptable, and to be acceptable it must first look and then taste 'right'.

In recent years we have become increasingly conscious of two other aspects of our food. As some of us have become more affluent, our food intake is no longer limited by our income and we have begun to suffer from the Western 'disease' of overnutrition. Our parents are appalled when our children follow sound dietetic advice and discard the calorie-laden fat from around their sliced ham and food scientists are called upon to devise butter substitutes with minimal fat content. Closely associated with this issue is the intense public interest in the 'chemicals' in our food. Sadly, the general public's appreciation of the terminology of chemistry leaves much to be desired. It is unlikely that many people would buy coleslaw from the delicatessen if the label actually listed the 'active ingredients':

ethanoic acid,

α-D-glucopyranosyl-(1,2)-β-D-fructofuranose,

p-hydroxybenzyl and indoylmethyl glucosinolates,

S-propenyl and other S-alkyl cysteine sulfoxides,

β-carotene (and other carotenoids),

phosphatidylcholine.

(The relationship of this list to the recipe for coleslaw will emerge later.)

The issue of 'chemicals' in food is closely linked to the pursuit of 'naturalness' as a guarantee of 'healthiness'. The enormous diversity of the diets consumed by Homo sapiens as a colonist of this planet makes it impossible to define the ideal diet. Diet related disease, including starvation, is a major cause of death but it appears that while choice of diet can certainly influence the manner of our passing diet has no influence on it's inevitability. As chemists work together with nutritionists, doctors, epidemiologists and other scientists to understand what it is we are eating and what it does to us we will come to understand the essential compromises the human diet entails. After all, our success on this planet is to some extent at least owed to an extraordinary ability to adapt our eating habits to what is available in the immediate environment. Whether that environment is an Arctic waste, a tropical rain forest, or a hamburger-infested inner city, humans actually cope rather well.

This book sets out to introduce the chemistry of our diet. The early chapters (2 to 5), covering food's 'macro-components' are more overtly chemical in character because these are the substances whose chemical properties exert the major influence on the obvious physical characteristics of foodstuffs....