Public confidence in food chain is under the spotlight

By Joseph James Whitworth

- Last updated on GMT

Related tags Government chemist Molecular biology Polymerase chain reaction

Picture: LGC. Horse meat being prepared for testing and for standard reference material production
Picture: LGC. Horse meat being prepared for testing and for standard reference material production
Public confidence in the UK food chain has come under particular spotlight after recent incidents, according to the UK Government Chemist’s annual review.

Supply chain complexity and products and manufacturing practices provide increasing challenges for the measurement community in building confidence in the marketplace, said the annual review.

Scientific advice and rigour around the testing regimes used to identify and semi-quantify adulteration levels of meat products during the horse meat scandal was one of the issues faced.

The Government Chemist resolve disputes between regulators and businesses as part of its statutory function, advises government on analytical science matters but also has commercial food analysis activities.

Issues being watched

Michael Walker, consultant referee analyst for the Lab of the Government Chemist (LGC), said food security and fraud will continue as an issue and tension will remain between lower limits of detection and speed.

“We are focussed around analytical techniques to beat cheats and we will continue to be demand led, not knowing what is coming to our doorstep.

“Aflatoxin cases will continue, maybe at the country of export it is fine and then when it lands at a port the aflatoxin is higher than the limits, because the type of sampling is not the same or for another reason.

“I hope we don’t see speciation issues as everyone should be on their guard and have well-controlled supply chains after horse meat.

“With allergies, the tracking of the supply chain is essential and not just one up and one down, you must have a relationship so you know what is coming and where from. Also cleaning is essential to prevent cross contamination and it needs to be validated.”

Walker said analytical chemistry and molecular biology were key tools in the process of technical standards and application validations.

“They are the only way to uncover these things as you can’t tell by looking at the product. Quality control and reference materials are needed as labs should know the context,” ​he said.

“Having a number is all very well but knowing the potential problems in analysis and issues in calculation to get the result and how to interpret that result is what is needed.” 

The Government Chemist was asked to investigate seven formal samples for which traders had lodged objections against the Public Analysts’ findings around the horse meat scandal.

In 6 out of 7 cases (86%) it confirmed the various Public Analysts’ findings, using polymerase chain reaction (PCR) DNA and enzyme linked immunosorbent assay (ELISA) methods.

Quantifying difficulties

There are difficulties in quantifying, by ELISA and DNA approaches, any one meat species in admixture with other species and ingredients, said LGC in its review​.

“It cannot be assumed that the amount of DNA present is a true reflection of the amount of meat present because the DNA may have been degraded during processing which may also, along with other ingredients affect the amount of DNA that can be extracted,” ​it said.

“In real-time PCR, the copy number of the marker gene (for the adulterant) is measured and compared to the copy number of a ‘normalising’ gene. This ratio can then be compared, with caution, to results from standard mixtures to infer the amount (e.g. percentage) of the adulterant.

“PCR suffers from inhibition and amplification efficiency issues due to matrix effects which can influence these calculations and although the variation is less problematic for foods with a limited number of ingredients, the results for composite ingredient foods have been found to be very variable.”

A fishy example

Walker gave an example of carbon monoxide (CO) in yellowfish tuna fish.

He said three consignments were referred to the Government Chemist by a trader who disputed the Public Analyst’s findings of CO in the fish.

“Carbon Monoxide is not a permitted additive, the fish can retain its pinky colour but it doesn’t stop it going off so the consumer is misled into thinking it is fresh.

“In this case the Public Analyst found CO, we found CO but it can be produced naturally in the metabolism of the fish at natural occurring levels.

“It was more likely natural rather than being added so we supported the trader as they didn’t do anything wrong. The appeal function can support an honest and responsible trader, in most cases we confirm the Public Analyst findings and reinforce the vigour and confidence in the system to protect consumer trust.”

The investigation was done by gas chromatography mass spectrometry (GC-MS).

In each case the lab confirmed the Public Analyst’s findings that the fish contained CO. However, between literature reviews, speaking with the FSA and European Commission, confirmed that CO treated products have consistently shown a content above 0.2 mg kg.

DNA method problems

The main problem for DNA methods lies in tension between detection and quantification, said LGC.

Mitochondrial detection is much more sensitive compared to nuclear genomic DNA, but it makes exact quantification almost impossible because of influencing factors.

“There is currently no officially recognised, standardised or approved approach for quantifying the levels of meat species adulteration…opinion is also divided between expressing results in terms of w/w tissue measurements or DNA/DNA copy numbers.

“…there is no direct conversion between DNA/DNA and w/w tissue measurements, and such a

comparison is affected by species, genome size, tissue type, matrix background, other ingredients, processing, level of degradation, and PCR efficiency.

“Despite the limitations, DNA approaches for meat speciation appear to be preferred because of potential advantages over protein detection methods, including specificity, sensitivity, the presence of DNA in virtually all tissue types, choice of targets and potential for development of a quantitative estimate without the risk of saturation (of antibody).”

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