Introduction

The chemists of the eighteenth and nineteenth centuries concentrated their efforts on the detection of food adulteration, detecting harmful ingredients (notably colourings) and protecting government revenue from the effects of the dilution and adulteration of wines and spirits etc. Twentieth century developments in physiology medicine stimulated the development of analytical techniques for proteins, sugars, etc. and also the vitamins and trace elements important in tiny amounts. Nowadays chemists are required to measure pesticide residues etc. at the parts per billion level. Chemists also study the behaviour of food components, during processing and culinary operations and their contribution to flavour, texture appearance as well as nutritional value. This activity is partly driven by the public's desire for the elusive property of "naturalness" in diet and recognition of the interactions between nutrition and sensory appeal.

For the chemists of the eighteenth and nineteenth 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 the first nutrients to be described in chemical terms. However, it was also widely recognised that much of the food, and the 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 Tatler, 1710.

However, by the nineteenth century the chemists had begun to expose some of the malpractices of food suppliers. In 1824 a local newspaper in the north of England reported on the chemical analysis of some confectionery: "One pennyworth of red balls, called we believe, Nelson or Waterloo Balls, – there were no such fine names in our lick-finger days, – yielded on analysis 30 grains of an indissoluble matter resembling red-lead, which on being fused with the blow-pipe produced 24 grains of lead in a metallic state ... ... ..."

A quarter of a century later a famous survey was published that revealed the extent to which the confectioners routinely borrowed colourings from the palettes of the painters (of both pictures and houses). Lead chromate (yellow), lead oxide (red), Prussian Blue (a mixture nominally described as ferric ferrocyanide), copper oxychloride (green), copper arsenite (green) and mercuric sulfide, vermilion (scarlet), were all in common use as food colours.

Chemistry was being brought to bear not only on the detection of dangerous colourings in confectionery but also on unwelcome use of many other unexpected food ingredients. A major incentive for the development of chemical analysis of food and drink 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 from the effects of the dilution and adulteration of wines and spirits etc.

As physiologists and physicians began to relate their findings to the chemical knowledge of foodstuffs the need for reliable analytical techniques increased. Twentieth century laboratory techniques were essential for the study of vitamins and the other components that occur in similarly small amounts, including the natural and artificial colouring and flavouring 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 now so sensitive that many food components can be detected and quantified at such low levels (parts per billion, i.e. 1 microgram per kilogram, are commonplace) that one can have serious doubts as to whether the presence of a particular pesticide residue, or environmental toxin, at the detection limits of the analysis can really have 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 middle years of the twentieth century 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. Chemists are nowadays expected to identify and quantify all the innumerable undesirable substances, both natural and man-made, which are to be found in our food. However, as reflected in this book, over the past few decades new questions have been asked and many of the answers are still awaited. The greatest challenge food chemists now face is to explain the behaviour of food components. What happens when food is processed, stored, cooked, chewed, digested and absorbed? Much of the stimulus for this type of enquiry has come from the food manufacturing industry. For example, for many of us 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 in behaviour between one starch and another. And, furthermore, that dessert product must have a long shelf life, look as pretty and taste nearly as good as the version served in an expensive restaurant.

Many of the changes in food materials during food processing, storage etc. are definitely chemical in nature, such as the reactions involved in caramelisation or rancidity. Other changes may involve less permanent types of chemical interaction, such as hydrogen bond formation in gel formation or the detection of sweetness by the tongue. However, some of the changes in food molecules are more biological in character – when reactions depending on enzymic catalysis are involved. Many of these reactions have been recognised for a long time but other enzyme based processes are quite novel. It was therefore important that this book now includes a chapter devoted to the mechanics, and applications, of enzyme catalysed reactions.

Issues of flavour and texture may seem somewhat superficial, even cosmetic, compared with the role of food as a supplier of essential...