Chapter 1: Introduction Free

During the eighteenth and nineteenth centuries, food became an important target for scientific investigators, particularly chemists. Alongside the medical profession, 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 organic, as opposed to mineral, nutrients to be described in chemical terms. However, it was also widely recognised that much of the food, and drink, available to the general public was likely to have been either contaminated accidentally or deliberately adulterated, often with the objective of enhanced profits for merchants and shop-keepers. Some of the chemists of the day took the blame for this:

The Tatler (1710)

Fortunately, by the beginning of the nineteenth century, chemists had begun to expose some of the malpractices of food suppliers. For example, in 1824, a local newspaper in the north of England reported on the chemical analysis of some confectionery sold to local children:

A quarter of a century later, a famous survey was published^iv that revealed the extent to which the confectioners routinely borrowed colourings from the palettes of 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 (scarlet) were all in common use as food colours. Unfortunately, the major incentive for the development of the chemical analysis of food and drink was actually financial rather public health. The UK 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.

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 isolation and 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 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 generations of food chemists that some of the methods of proximate analysis^v that they struggled with in the 1960s are still in use today, albeit in automated apparatus rather than using extravagant examples of the laboratory 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 the general public had been answered. This was certainly true as far as questions of the “What is this substance and how much is there in …?” variety were concerned. Such questions not only concerned the obviously desirable nutrients, but also the substances that give our foods their characteristic – and desirable – flavours, colours and textures. At the same time, chemists were called upon to address the growing lists of undesirable substances, either naturally occurring or the products of chemical synthesis, that find their way into our food.

Throughout the second half of the twentieth century, biochemistry moved on from the two-dimensional structural formulae that abound in textbooks (such as this one) to the three-dimensional views that describe the shapes of molecules, even of the very largest proteins and polysaccharides. This has allowed us much deeper insights into the interactions between molecules – not only in living tissues, but also in the once-living tissues that constitute our food after we have harvested, preserved, processed and cooked it. We now recognise that these interactions between individual food components may reduce, or enhance, their nutritional value as well making them more or less appealing or digestible. 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 (possibly more than we actually require) 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. Furthermore, that dessert product must have a long shelf life, look as attractive and taste (nearly) as good as the version served in an expensive restaurant or its home-made equivalent.

Many of the changes in that take place in food materials during processing, storage etc. are definitely chemical in nature, such as the irreversible reactions involved in caramelisation or rancidity. Other changes may involve less permanent types of chemical interaction, such as when hydrogen bonds are involved in the formation of polysaccharide or protein gels. Some of the changes that occur in food materials, during storage or processing, are more biological in character, involving reactions catalysed by enzymes. Many of these reactions depend on the enzymes naturally present in food raw materials and have been unwittingly exploited for centuries, but only understood in recent years. However, in recent decades food processing operations that depend the use of enzymes from other sources, particularly microorganisms, have become increasingly significant. It is therefore important that this book includes a chapter devoted to the mechanics, and applications, of enzyme-catalysed reactions in the context of food product manufacture.

In recent years, we have had to come to terms with much wider aspects of food production and supply. Ordinary consumers may aspire to the gourmet dishes that popular media tell us are the normal diet of the rich and famous. However, the populations of less affluent nations similarly, and rightly, aspire to the varied, and often meat-containing, diets enjoyed elsewhere. We can no longer ignore the environmental and economic implications of these pressures – for example, the supply of soya protein for feeding cattle or the clearance of natural forests for oil palms. Of course, food chemistry alone cannot answer these questions, but as readers of this book will discover, it can make valuable contributions to the considerations of these issues.

Issues of flavour and texture may seem superficial, even cosmetic, compared with the dual roles of food as a supplier of essential nutrients and as a vehicle for natural and synthetic toxins. However, these apparently superficial aspects of food are actually of great importance. Nutritionists, physiologists and other scientists now recognise what consumers have always known – there is much more to the business of feeding people than assembling a list of nutrients in the correct proportions. This might be obvious in the supply of food in relatively affluent communities, but it is just as true if one is engaged in famine relief. To satisfy a nutritional need, a foodstuff must be acceptable and recognised for what it is, and that means looking and tasting “right”. We are now much more aware of two other aspects of our food. First, 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 over-nutrition. Food scientists are now called upon to devise butter substitutes with minimal fat content, low-sugar, but tasty, breakfast cereals and low-salt/low-fat snack foods.

Closely associated with this issue is the intense public interest in the “chemicals” in our food. In the 1950s, the author’s first chemistry teacher, Mr Crosland, refused to allow the word “chemical” to be used as a noun. It is the author’s view a great pity that this attitude has never found wider acceptance. The general public’s limited appreciation of the language of chemistry continues to leave much to be desired – a situation the popular media and its self-appointed pundits never hesitate to exploit. One result is that it is unlikely that many people would readily buy coleslaw from the delicatessen if it carried a label like this.

All the substances in this list have the unifying characteristic that they are naturally occurring components of one or other of the raw materials that consumers would expect to find in coleslaw, whether or not it was a commercial product. Of course, many modern food products also contain ingredients that can be described as “additives”. According to the UK Food Standards Agency, additives are “Ingredients that are added to foods to carry out particular functions” without being nutrients in their own right. These functions are normally considered to include a food’s safety, freshness, taste, texture or appearance. The functions of particular types of food additives are dealt with in this book from a chemical point of view, but details of their regulation and legislation, which, of course, vary from country to country, are largely outside its scope and the expertise of its author.^vi

The issue of chemicals in food is also closely linked to the pursuit of “naturalness” as a supposed guarantee of “healthiness”. The enormous diversity of the foodstuffs consumed by Homo sapiens as a colonist of this planet makes it difficult to define the ideal diet. Diet-related disease, including starvation, is a major cause of death, but it appears that although our choice of diet can certainly influence the manner of our passing, diet has no influence on its 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 steadily increase our understanding of the essential compromises the human diet entails. After all, our success on this planet is to some extent at least owed to our 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. Chapters 2–5 and 13 cover food’s macro-components – the carbohydrates, lipids, proteins and water – and these chapters are more obviously chemical in character. These are the substances whose chemical properties exert the major influence on the obvious physical characteristics of foodstuffs. If we are to understand the properties of food gels, we are going to need a firm grasp of the chemical properties of polysaccharides. Similarly, we will not properly understand the unique properties that cocoa butter gives to chocolate without becoming involved in the crystallography of triglycerides.

Chapters 6–11 are devoted to substances drawn together by the nature of their contribution to food, positive or negative, rather than by their chemical classification. For example, on the one hand we have colours, vitamins, etc., and on the other mycotoxins, packaging residues, etc. Although this means that less attention can be devoted to the chemical behaviour of these substances individually, there is still much that the chemists can contribute to our understanding of flavour, appearance and nutritional value. Science is rarely as tidy as one might wish and it is inevitable that some food components have found their way into chapters where it might be thought they do not really belong. For example, some of the flavonoids mentioned in Chapter 6 make no contribution to the colour of food. However, in terms of chemical structure and behaviour, they are closely related to the flavonoid anthocyanin pigments and Chapter 6 may be regarded as a good a location for them as any.

Chapter 12 is devoted to enzymes. It is the reactions that enzymes catalyse that reveal their presence to us, rather than their chemical nature. All life depends on the activity of enzymes and every foodstuff, being biological in nature, comes to us in its raw state containing a multitude of different enzymes. Most we can ignore, some we need to inactivate to ensure the stability of nutrients, etc., but others we have learned to exploit in the production of many food products.

The final chapter, Chapter 13, is devoted to water. Apparently the simplest of all our food’s components, and certainly the most abundant, the actual complexities of water’s behaviour and interactions with other food components have, until recently, tended to be overlooked.

This book does not set out to be a textbook of nutrition; this is outside the field of the author’s expertise. Nevertheless, food chemists cannot ignore nutritional issues and wherever possible the links between the subtleties of the chemical nature of food components and nutritional and health issues have been pointed out. Similarly, students of nutrition should find a greater insight into the chemical background of their subject valuable. It is also to be hoped that people who campaign for the reduction or increase of this or that component of our diet to improve our health will gain a better appreciation of exactly what it is they are demanding, and its wider potential implications.

Food chemists should never overlook the fact that the object of their study is not just another, albeit fascinating, aspect of applied science. It is all about what we eat, not just to provide nutrients for the physical benefit of our bodies, but also to give pleasure and satisfaction to the senses. Not even the driest old scientist compliments the cook on the vitamin content of the food on his or her plate – it’s the flavours and the textures, and the company around the table, which win every time.

• H. McGee, On Food and Cooking, Unwin Hyman, London, 1984.

• J. Burnett, Plenty and Want: A Social History of Diet in England from 1815 to the Present Day, Routledge, London, 3rd edn, 1989.

• M. Toussaint-Samat, History of Food, Blackwell, Cambridge, MA, USA, 1992.