Food Fighters – measurement to combat food adulteration
17 Apr 2012 by Evoluted New Media
How science is facing up to food fraud
Picture the early 1800’s where the deliberate adulteration of food was common practice. Spent tea leaves were made to look like the genuine article by boiling them with ferrous sulphate and sheep’s dung. Poisonous compounds containing lead, copper or mercury were added to sweets to enhance their colour. Bitter tasting substances, many containing poisons such as strychnine, were added to beer to enhance its flavour and to save on the cost of hops, while bakers often added alum, chalk or powdered bones to give the bread a white appearance.
Thankfully times have changed, but food fraud still exists today. However, the majority of cases are driven by economic motives such as the deliberate mis-categorisation of food, for example substituting a key ingredient with a cheaper option or selling farmed salmon as wild salmon. Whilst this is not necessarily unsafe to us as the consumer, it does deceive us to the nature of the product we are purchasing.
The role of the Government Chemist in the UK provides an independent voice and expert opinion based on sound analytical measurement science to help avoid or resolve disputes pertaining to food and agriculture in order to protect the public. The Government Chemist function has been in place since 1842 when the first Government Chemist, George Phillips was appointed. Since the early 19th Century, the nature of food adulteration has changed. However best practical methods of measurement and sound analysis are still relied upon today to solve complex food cases.
During 1900, in Salford, Manchester, the scandal of the ‘poisoned pint’ erupted. People started complaining of weakness and pain in the limbs, general numbness and rheumatism, and even paralysis. It was reported that 41 people died due to peripheral neuritis, multiple neuritis or alcoholic neuritis. The symptoms pointed to arsenic poisoning. The Government Chemist traced the outbreak to beer and then back to the glucose used in its manufacture. This glucose was found to have been supplied by a Liverpool firm of brewing sugar manufacturers and beer made from the product containing arsenic was eventually found over much of northern and midland counties. The arsenic was traced to the sulphuric acid used in the preparation of the glucose from cane sugar1.
Interestingly, around the same time, the Government Chemist – following a personal request from Captain Scott – undertook research which exposed a nutritional deficit in the food supplies planned for use in Scott’s 1901 scientific and geographical expedition to the Antarctic. Pemmican, a primary food source rich in energy, was supposed to contain 60% ox fat with virtually no moisture for prolonged storage. On examination by the Government Chemist, the Pemmican samples were found to contain only 19.6% ox fat. It has also been reported that the samples analysed contained pieces of broken metal. On results of the Government Chemists’ analysis, Scott chose an alternate supplier of Pemmican. Analysis of samples from these new suppliers showed nutritional content to be “rather more satisfactory”2.
Whilst arsenic poisoning is an extreme case, the Government Chemist routinely analysed beer for dilution or adulteration and tobacco, milk and bread for quality. Butter adulteration appeared to be a consistent problem with the presence of boric acid being regularly identified. In order to obtain information on the composition of butter with a view to fixing standards for minimal limits of quality, the Government Chemist, in collaboration with the Board of Agriculture, drew up a scheme for the collection of genuine butter samples from different districts, during various seasons of the year2.
Adulteration cases such as these are very rare in today’s highly regulated global food industry, yet 96 people were recently detained in southern China when boric acid was found in tofu. It is estimated the economic adulteration and counterfeiting of the global food source is expected to cost the industry $10 to $15 billion per year3.
Today the duties of the Government Chemist focus on public protection, safety, health, value for money, and consumer choice. Much of the work relates to scientific dispute resolution – ‘referee analysis’ – to resolve a dispute over tests carried out on behalf of an enforcement authority and a trader during a formal investigation. Test samples are divided into three parts by an authorised officer. Both parties have the opportunity to perform independent analysis, while the third part of the sample is retained in case the referee is called upon to act. A Government Chemist referee analysis and opinion can be obtained without recourse to the law courts or, if a judge orders the referral, can be adduced to minimise the trial costs.
After an anonymous tip off, a UK Local Authority found that raspberry sauce had been substituted by strawberry sauce in an ice cream product. The food business disputed the official findings and the Government Chemist was called in to resolve the issue. Complicated by the complex ice cream matrix, this offered an analytical challenge that required three analytical approaches (microscopy, DNA and LC-UV of anthocyanins) in order to solve it. Bright field high power microscopy was used to identify the characteristic trichomes (plant hairs) that differ in morphology and abundance in the raspberries and strawberries (Figure 1).
Microsatellite markers (short tandem repeats) present in the DNA and specific to strawberry or which allow differentiation between strawberry and raspberry were amplified by PCR4. Finally, extracted anthocyanins analysed by LC-UV and by LC-MS/MS enabled discrimination between fruits. Based on the three analytical approaches, the Government Chemist confirmed that three of the six samples provided contained strawberry and three contained raspberry. The findings broadly confirmed those of the public analyst, that different tubs of ice cream contained different sauces – some strawberry and some raspberry. This can only have occurred because a container of strawberry sauce was erroneously fed into the production process at some point.
In addition to settling disputes, the Government Chemist helps avoid them. The UK code of practice for basmati rice requires at least 93% of the grains of rice in a sample to meet the label description. A formal sample described as basmati rice was tested by a Public Analyst and found not to comply. A separate sample was sent to an independent laboratory which reported borderline compliance. The Government Chemist advised on the case at several stages and proposed further sampling.
No further action was taken however, because it appeared that the manufacturer might reasonably plead due diligence, a defence recognised by section 21 of the Food Safety Act 1990, and other sectoral legislation. The Government Chemist is 
now developing guidance for rice sampling to ensure traceable, comparable sampling in future cases.
Fish fingers are normally made from "white fish". Originally the fish of choice was cod, but depleted stocks have led to the use of other fish. Many products are now labelled as containing "fish" or "white fish", which allows the manufacturers to use fish from a variety of sources. In order for consumers to make informed choices, food law requires pre-packaged food such as fish fingers to be labelled with a declaration of the amount of fish present.
In a recent case, a product was labelled with the declaration of "65% Minced White Fish". Analysis of a portion of the sample by the Public Analyst had shown that the amount of fish present was lower than the declared fish content. The Government Chemist was asked to carry out a definitive analysis of the fish content of the sample. Food law in the EU (Directive 2000/13/EC) requires a quantitative ingredient declaration (QUID) of the amount of fish for pre-packed products. The quantity should be calculated on the basis of fish expressed as a percentage of the total weight of all the ingoing ingredients (except for the weight of added water or volatile ingredients lost in processing). However, there is no direct method for the determination of the fish content of a product. In 1919 Stubbs and More, working in the Laboratory of the Government Chemist, developed a method for the determination of the meat content of a product that is widely accepted and based on the amount of nitrogen, compared to the mean nitrogen content of the species5. The nitrogen factor is the mean value for the percentage nitrogen content of species of fish used and varies naturally, even within the same species, due to factors such as different fishing grounds, size, sex or spawning cycles6. To avoid overestimating the fish content, nitrogen that does not originate from fish must be excluded from the calculation.
[caption id="attachment_27629" align="alignright" width="200" caption="Figure 1: Raspberry trichomes are short and very sinuous and up to 0.7mm in length (A), whilst strawberry trichomes are relatively straight, gradually tapering and often more than 1mm long (B)"]
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The fish finger sample was divided into two equal portions. The breadcrumbs and coating were removed from the flesh in one half of the sample, then the flesh was blended and analysed for proximates (i.e. moisture, nitrogen, fat and ash) using methods which were originally recommended by the Analytical Methods Committee and have been subsequently adopted as British Standards. With the other half of the sample, the entire product was blended and proximates determined. Treating the sample in this manner allowed corrections to be made for sources of non-fish nitrogen. The Trading Standards led the joint prosecution, resulting in the trader pleading guilty to two offences of falsely describing the fish content of fish fingers contrary to Section 15(1) (a) of the Food Safety Act 1990.
Referee analysis prompts tactical research on related sample types and development of measurement methods. Stakes are high, so the credibility of the referee rests on first-class science. LGC’s role as the UK’s designated National Measurement Institute (NMI) for chemical and bioanalytical measurement strategically underpins and adds value to the Government Chemist function, providing access to advanced measurement facilities and reducing investment costs.
Part of LGC’s NMI’s research using mass spectrometry has focused on the investigation of the feasibility of methods based on isotope ratio measurements to discriminate between geographical provenance, for example, origin of a food source or origin of counterfeit drug manufacture. Through natural processes, isotope ratios change from place to place on the globe. Research is underway across the UK to see where these effects can be used to pin-point geographical origin. Laboratories are differentiating beef origin across Britain and between Brazil and Britain. Similar studies have assisted forensic science, for example leading to geographical information on the ‘torso in the Thames’ – the case of a torso found in the River Thames, London on 21 September 2001 belonging to a young unidentified African boy. Post mortem on his bones, stomach contents and pollen in his lungs was used to determine his geographical origins and the length of time he had spent in the UK.
As a member of the Forensic Isotope Ratio Mass Spectrometry (FIRMS) Network, LGC has recently collaborated on the publication of a ‘Best Practice Guide’ for isotope ratio mass spectrometry7. A key activity for LGC as an NMI is the development of ‘Best Practice Guides’ and training resources to assist laboratories in making fit for purpose measurements.
LGC is evaluating multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) as a tool for the direct measurement of sulphur stable isotope ratios in beers as a first step toward a general study of the natural isotope variability of sulphur in foods and beverages8.
The main problem affecting isotope ratio measurements by MC-ICP-MS is the existence of matrix effects on the mass bias correction factor. The transmission of the ions in the mass spectrometer will change slightly in the presence of high concentrations of the matrix, and this change will not be the same for different isotopes of the same element. Therefore, apparent changes in isotope ratios could be due to matrix effects and not to real changes in the sample. There are different alternatives to eliminate or correct for these matrix effects. The traditional solution is the separation of the element from the matrix and the use of a certified isotopic standard of the element for external mass bias correction. As an alternative, internal mass bias correction using another element close in mass can be applied.
Whilst this is not necessarily unsafe to us as the consumer, it does deceive us to the nature of the product we are purchasing.Previous research has suggested that for sulphur measurements, silicon internal standardisation can be used to correct for mass bias effects. Using 26 beer samples, the capabilities of silicon for the correction of mass bias related matrix effects for the determination of sulphur natural isotope variations by MC-ICP-MS have been demonstrated as a potential method. This opens the way for large studies on sulphur isotope variations in foods and beverages using this very simple sample preparation.
Genetically modified (GM) foods and other types of novel foods can only be marketed in the European Union (EU) if they have passed a rigorous safety assessment. EC regulation 1829/2003 specifies that food products which contain GM material must be clearly labelled. Currently, materials that are produced under an identity-preserved scheme must be labelled if the level from EU approved GM varieties exceed a 0.9% threshold for adventitious contamination. The threshold value refers to the proportion of GM food in any single ingredient of a foodstuff and is not in relation to the total mass of the entire food product. For this to be reliably upheld there is a need for international measurement traceability and comparability.
NMIs participate in and organise comparison studies to demonstrate measurement capabilities and benchmark against international peers. The CCQM (Consultative Committee for Amount of Substance) of the International Bureau of Weights and Measures (BIPM) coordinates these studies, the results of which are used to establish the equivalence of the measurements. This measurement equivalence is essential to underpin global trade, facilitate innovation and demonstrate regulatory compliance.
For GM foods, the quantification of the relative amount of DNA sequences is a complex analytical procedure. Real-time quantitative polymerase chain reaction (qPCR) is currently the most applied measurement method to identify and quantify DNA sequences. A recent CCQM study was performed to demonstrate the capability of the NMIs to determine the relative quantity of two specific genomic DNA fragments present in ground maize seed. Good agreement was observed between the results of 11 NMIs. Several different extraction methods were applied to extract the DNA from the maize, leading to similar final results suggesting that the DNA extracted was of similar quality and purity for amplification by PCR9.
These cases demonstrate how measurement research supports the food industry in producing food that is safe for consumers and protects consumers from food fraud. Through developing improved measurement capabilities the Government Chemist also helps prepare the UK to meet future demands in food safety.
References
1 Hammond PW and Egan H, Weighed in the balance, HMSO (1992)
2 Annual reports of the Principal Chemist, 1897-1911
3 Grocery Manufacturers Association (GMA) and A. T. Kearney Consumer product fraud: deterrence and detection, 2010
4 Burns M, Sanders R and Burrell A, Strawberry and Raspberry Fruit Differentiation Using the Agilent CE 2100 Bioanalyzer, Agilent website, 2009
5 Stubbs & More, The estimation of the approximate quantity of meat in sausages and meat pastes, Analyst, 44, 125-127, 1919
6 Colwell P, Ellison S, Walker M, et al., Nitrogen Factors for Atlantic Salmon, Salmo salar, farmed in Scotland and in Norway and for the derived ingredient, “Salmon Frame Mince”, in Fish Products, JAPA, 39, 44-78, 2011.
7 Carter J, Barwick V, Good Practice Guide for Isotope Ratio Mass Spectrometry, ISBN 978-0-948926-31-0, 2011
8 Ginger Marti´Nez-Sierra J, Santamaria-Fernandez R, Hearn R et al., Development of a Direct Procedure for the Measurement of Sulfur Isotope Variability in Beers by MC-ICP-MS, J. Agric. Food Chem., 58, 4043–4050, 2010.
9 Corbisier P, Vincent S, Schimmel H et al., CCQM-K86/P113.1: Relative quantification of genomic DNA fragments extracted from a biological tissue, Metrologia, 49, 08002, 2011.
The Author Louise Dean LGC, Science & Technology Division Louise is responsible for delivering the knowledge transfer projects under the UK National Measurement System's 'Chemical and Biological Metrology Programme', disseminating measurement research to industry and academia
