The global food system in the 21st century faces considerable challenges:
“The needs of a growing world population will need to be satisfied as critical resources such as water, energy and land become increasingly scarce. The food system must become sustainable, whilst adapting to climate change and substantially contributing to climate change mitigation. There is also a need to redouble efforts to address hunger, which continues to affect so many.”
Professor Sir John Beddington, former Government Chief Scientist, 2011, Foresight: Future of Food and Farming1
We face unprecedented change in the way we need to grow, produce and manufacture food to ensure we have a sustainable, resilient and secure supply for future generations. Our supply chain must also sustain consumer confidence if we are to grow and maintain a competitive and thriving food industry. Knowing the ingredients of a particular food, how it was produced, where it comes from and that it is correctly labelled, are a key part of assuring the integrity of the food system. These are the central elements of food authenticity. It is also essential that we have test methods to assess the authenticity of foods – the expertise of the contributors to this book has led to the development of many such methods in use today.
Why is DNA of such importance as a marker of food authenticity? Because food authenticity often turns on the question of what a food is – its nature or substance1 and how it is described. DNA (Box 1.1) provides an unequivocal answer to these questions. DNA-based methods to determine the authenticity of food were developed over 20 years ago but it was the horse meat incident in 2013 2 that provided the impetus for a major change in the way in which we conduct DNA analysis.
(Molecular biologists may skip this…)
Nucleic acids were first isolated from cell nuclei over 100 years ago. DNA, deoxyribonucleic acid, is found in virtually every plant, micro-organism and animal cell, with the exception of mature human red blood cells, which lose their nuclei as they grow. Chromosomes, in the nucleus of each cell and only visible (microscopically) when the cell is dividing, are thread-like structures of DNA tightly coiled many times around supporting proteins (e.g. histones).8 Genetic information in segments of the chromosomes called ‘genes’ carry instructions from one generation to the next for the growth, development and functioning of the living organism. Genes control cell growth and division and code for the biosynthesis of enzymes and other proteins required for cellular function. The information encoded in DNA is translated into protein via ribonucleic acid (RNA). The now famous double helix structure of DNA was elucidated in 1953 by Francis Crick and James Watson based on previous studies and X-ray diffraction data from Maurice Wilkins and Rosalind Franklin.9
If the helical structure of DNA is regarded simplistically as a ladder (Figure 1.1) the ‘uprights’ are polymeric chains of phosphoric acid esterified with a pentose sugar, deoxyribose2, and the ‘rungs’ are heterocyclic amine bases3. Two of the bases are substituted purines: adenine (A) and guanine (G) and two are substituted pyrimidines: cytosine (C) and thymine (T)4. The bases are bonded to the deoxyribose sugar by an N-glycosidic link hence they are termed nucleosides. The atomic numbering system in the sugar moiety is 1′ to 5′ (1 prime to 5 prime) thus distinguishing these from the atoms in the heterocyclic amine bases. The 5′-OH group of the sugar portion of the nucleoside esterified with phosphoric acid forms the nucleoside-5′-phosphate or nucleotide. In summary, nucleic acids, such as DNA5 are polymers of nucleotides and DNA has a direction – one end of the nucleic acid polymer has a free hydroxyl at C3′ (called the 3′ end) and the other end has a phosphate residue at C5′ (the 5′ end) (Figure 1.2).
Simplified diagram of DNA double helix. Reproduced from ref. 21 with permission from the Royal Society of Chemistry.
Simplified diagram of DNA double helix. Reproduced from ref. 21 with permission from the Royal Society of Chemistry.
Showing a labelled section of the DNA molecule. Reproduced from ref. 22 with permission from the Royal Society of Chemistry.
Showing a labelled section of the DNA molecule. Reproduced from ref. 22 with permission from the Royal Society of Chemistry.
While the nucleotides themselves are covalently bonded, Crick and Watson proposed, and it is now well known, that hydrogen bonding between the heterocyclic amine bases plays a large part in the formation and stability of the double helix structure of DNA. Strong attraction is generated between two (A and T6) or three (C and G7) pairs of atoms (Figure 1.3). Thus two complementary single strands of DNA form the double stranded molecule on which genetic information is inherent. Conventionally, the symbolic shorthand notation reflects this, for example a base pair sequence might be written as:
Hydrogen bonding in the DNA double helix. Reproduced from ref. 22 with permission from the Royal Society of Chemistry.
Hydrogen bonding in the DNA double helix. Reproduced from ref. 22 with permission from the Royal Society of Chemistry.
These molecular geometries and hydrogen bonding energy profiles result in the self-assembly, replication and amplification properties of DNA.
Further Reading
H. Beyer and W. Walker, Organic Chemistry, A Comprehensive Degree Text and Source Book, ed. and Trans., Douglas Lloyd, Albion Publishing, Chichester, 1997, pp. 849–859.
P. Madesis, I. Ganopoulos, I. Sakaridis, A. Argiriou and A. Tsaftaris, Advances of DNA-based methods for tracing the botanical origin of food products, Food Res. Int., 2014, 60, 163–172.
Why is food authenticity important? We have an intimate relationship with food going far beyond its nutritive value into cultural and interpersonal meaning. The authenticity of the food we buy and eat is of visceral significance. Given the time, opportunity and experience we can appraise food visually, and by smell and taste. But we must often take authenticity on trust – when the food's description becomes the key. If that trust is betrayed by misdescription on a personal level we feel cheated. Economically there is loss of ‘value for money’, which many can increasingly ill afford.3,4 Loss of trust at a societal level causes reputational damage to individual companies and difficult trading conditions for whole sectors.5 In some situations individual consumers may come to actual harm, as shown by food allergen fatalities caused by, at times fraudulent, substitution.6 Misleading a purchaser about food authenticity is illegal, potentially harmful, penalises the honest trader, and undermines consumer choice and value for money. In general, when driven by financial gain it is food fraud and when particularly serious, and involves intentional dishonesty detrimentally affecting the safety or authenticity of food, it is food crime7 (Box 1.2).
Concerns that food should be true to its description are not new – food has probably been adulterated since trade commenced.10 ‘Adulteration’ has been the traditional concept to describe food that is unsafe or misdescribed. Scientific appraisal of food began in earnest in the latter half of the 19th century11 when major advances were made in food science, often by researchers charged with upholding newly introduced food law, in the UK the Public Analysts.12–16
False claims about any of the properties of marketed food have been regarded as fraud at least since the 19th century17 and food fraud is now understood to involve any dishonest act or omission relating to the sale or preparation of food intended for personal gain or to cause loss to another party. Economically motivated adulteration is another frequent phrase applied. However, the concept of ‘food crime’ was largely introduced by Professor Chris Elliott during his review18 into the integrity and assurance of food supply networks in the aftermath of the horse meat scandal. Although anything other than authentic food is illegal there is a gradation of seriousness (Figure 1.4) and the National Food Crime Unit (NFCU) of the Food Standards Agency (FSA) and the Scottish Food Crime and Incidents Unit, (SFCIU), define food crime as “… dishonesty in food production or supply, which is either complex or results in serious harm to consumers, businesses or the public interest”.19
Gradation of seriousness of food illegality.
The NFCU further identify20 seven techniques as the main methods through which food crime can be committed:
theft – dishonestly appropriating food, drink or feed products in order to profit from their use or sale
unlawful processing – slaughtering or preparing meat and related products in unapproved premises or using unauthorised techniques
waste diversion – unlawfully diverting food, drink or feed meant for disposal, back into the supply chain
adulteration – reducing the quality of food by including a foreign substance, in order to lower costs or fake a higher quality
substitution – replacing a food or ingredient with another substance that is similar but inferior
misrepresentation – marketing or labelling a product to wrongly portray its quality, safety, origin or freshness
document fraud – includes the making, use and possession of false documents with the intent to sell, market or otherwise vouch for a fraudulent or substandard product.
Thus, this book takes the analyst on a ‘food forensics’ journey, setting out how DNA technology, originating in criminology, has paved the way for the successful application of the sophisticated analytical tools we have today to verify food authenticity. It describes the range of tools available, how they have evolved, and how analytical confidence in these methods has been developed. It also describes the practical challenges associated with the application of DNA tools for ‘fit for purpose’ analysis for industry and enforcers alike. Some of these challenges, and the step changes in science development to tackle them, are brought to life through a series of case studies.
More broadly, this book provides a European Union (EU) perspective on how authenticity methods and approaches are being harmonised and standardised, drawing heavily on the ‘Genetically Modified Organisms (GMO) story’; and charts EU cooperation on food integrity research over the past 20 years. It also provides an international insight on issues such as food fraud and verifying authenticity of traditional medicines. Finally, looking forward, some of the exciting new developments in DNA analysis and how these are paving the way for future ways to tackle food fraud are explored.
We trust you will enjoy reading the book, perhaps learn from it, and if you spot any (inevitable) errors please let us know. Please also note that any views expressed are those of the editors or chapter authors personally and not those of the Royal Society of Chemistry, Government Chemist, the Department for Environment, Food and Rural Affairs, the Department for Business, Energy and Industrial Strategy or chapter authors' institutions.
The terms ‘nature’, ‘substance’ (and ‘quality’) applied to food have a special significance in food law, see Chapter 10.
‘Deoxy’ signifying that one of the sugar hydroxyl groups has been replaces by hydrogen.
For example the lone pair of electrons on the –NH of adenine and guanidine feed into the heterocyclic ring to increase electron density and hence basicity on the other nitrogens.
The symbols A, G, C and T may refer to nucleosides, deoxynucleosides, or nucleotides when specifying base-pairing or nucleotide sequences.
And RNA, where thymine is replaced by the pyrimidine uracil.
=N–H…O= and ≡N…H – N=[… Indicates hydrogen bonding].
=O…H–N=, =N–H…N≡ and =N–H…O=.
