Food: The Chemistry of its Components
Preface to Sixth Edition
Published:09 Oct 2015
When the Royal Society of Chemistry first invited me to write this book in 1980 the proposed readership was clearly delineated, namely teachers of GCE Advanced Level Chemistry in school 6th forms. Apparently they were badly in need of background information to help them prepare their students for the new topic of Food Chemistry that had appeared on some of their syllabuses. By the time the first edition actually appeared (in 1984) the need for an up to date textbook of introductory food chemistry to support my own BSc Food Science students (at what was then the Polytechnic of the South Bank, London) was also becoming obvious. The favourable response to the first edition told me that for once two birds had been hit with one stone! As new editions have appeared over the years the original objective has, perhaps inevitably, suffered from what I believe is known in military circles as ‘mission creep’. This edition is more than double the size of the first, as interesting new topics have demanded attention and chapters devoted to water, minerals, undesirables and enzymes have been added.
My determination to ensure that the chemical formula is included for virtually every food substance mentioned in the text may make the contents look a little intimidating. However I have always tried to make the actual words as approachable as possible, lending themselves to being ‘read’, even ‘browsed’ as well as ‘looked up’. In spite of appearances readers with only modest recollections of school chemistry should find much that is within their grasp, especially in the later chapters.
As in previous editions a selection of texts for ‘Further Reading’ is appended to each chapter, wherever possible restricted to 21st century editions. Extensive references to research literature are not included but each chapter concludes with a selection of relatively recent review articles which will provide access to the original research. By the use of citation indexing (e.g. Google Scholar or the Science Citation Index) the same article may continue to provide an entry into the most recent literature for many years and certainly the lifetime of an edition of a textbook such as this.
The temptation to include addresses of relevant and authoritative websites has generally been resisted since, unlike the printed scientific literature, websites tend to be rather ephemeral and unlikely to remain available throughout the lifetime of a textbook. Undoubtedly the internet can provide a wealth of information but it must be used with very great caution. It has always been the case that one should not necessarily believe something just because it was printed in a book, but such cynicism is absolutely essential when looking at websites. One exception is legislative and other official information published by legislative authorities and other similar organisations. This material is frequently very difficult to obtain in print and appropriate websites are listed in Appendix II. All these sites were accessible in 2015. The appropriate authorities, such as in Britain the Food Standards Agency, must always be consulted when accurate details of the legal position regarding, for example, the use of a particular food additive, are called for.
A brief note on concentrations
The concentrations of chemical components are expressed in a number of different styles in this book, depending on the context and the concentrations concerned. Some readers may find the following helpful.
However they are expressed, concentrations always imply the amount contained, rather than added. Thus “5 g of X per 100 g of foodstuff” implies that 100 g of the foodstuff contains 95 g of substance(s) that are not X.
The abbreviation “p.p.m.” means “parts per million” i.e. grams per million grams, or more realistically milligrams per kilogram. One “p.p.b.”, or part per billion, corresponds to one microgram per kilogram.
Amounts contained in 100 g (or 100 cm3) are often referred to as simple percentages. Where necessary the terms “w/w”, “v/v” or “w/v” are added to indicate whether volumes or weights or both are involved. Thus “5% w/v” means that 100 cm3 of a liquid contains 5 g of a solid, either dissolved or in suspension. Although the millilitre (ml), cubic centimetre (cc) and litre (l) are no longer officially regarded as SI units they are widely used, by both the scientific community and the general public. Although the replacement for the ml, ‘the centimetre cubed’ (“cm3”) is widely recognised there is little sign that the cubic decimetre, or “dm3” has taken over from the litre, except in school and college teaching laboratories that must always be seen to ‘toe the party line’. As might be expected different abbreviations for the litre are in use on the different sides of the Atlantic, in the USA “L” is preferred, in Europe (and in this book) “l”.
- Very often a strictly mathematical style is adopted, with “per” expressed as the power of minus one. Since mathematically:5 mg kg−1 becomes a convenient way of writing 5 micrograms per kilogram. This brief but mathematically rigorous style comes into its own when the rates of intake of substances such as toxins have to be related to the size of the animal consuming them, as in “5 milligrams per day per kilogram body weight”, which abbreviates to:x−1=1/x5 mg day−1 kg−1 body weight
The term “body weight” may be abbreviated to “bw” or in some contexts omitted altogether. A concentration, say 10 mg per cubic centimetre, cm3, would be written: 10 mg cm−3.