Gov Chemist: Sulphite determination was most challenging investigation

By Joseph James Whitworth

- Last updated on GMT

Picture: iStock/fotohunter
Picture: iStock/fotohunter

Related tags Government chemist

Determining low concentration levels of sulphites in foods such as garlic was the most challenging investigation last year due to interferences, according to the Government Chemist Annual Review.

The agency was asked to look into possible undisclosed addition of sulphites close to the cut-off concentration of 10 mg kg-1 in a niche product containing several known interfering foods.

Sulphites describes a range of permitted food additives that consist of or generate sulphur dioxide, SO2​, the active compound, in food.

It is the only non-protein allergen group and disclosure is required if present in food to protect consumers.

Undisclosed addition of sulphites  

Reference methods are variations of the Monier-Williams procedure which is interfered with positively by dried garlic and soya proteins and to a lesser extent by onions and cabbage.

They found that only LC-MS/MS methods, owing to chromatographic separation and mass spectrometric identification, gave sufficient confidence to results.

However, investigations continue to develop a method to achieve the rigour desired in a referee analysis.

During 2016, eight cases were referred to the Government Chemist – seven in connection with food and one with animal feed. This is down from 14 cases in its referee function in 2015 and 16 the year before.

LGC hosts the role of Government Chemist, providing expert opinion, based on independent measurement, to help avoid or resolve disputes around food and agriculture.

Last year, the Government Chemist team participated in a ring trial using Next Generation Sequencing (NGS) technology for authenticity testing as part of the DECATHLON project.

It also has an ongoing collaboration with Manchester University in allergen research.

Mycotoxins, authenticity and protein allergens

Referee analysis work during 2016 also included measurement disputes relating to mycotoxins, authenticity and protein allergens.

Derek Craston, of the Government Chemist, said it is important to prepare and predict future issues and be timely in reporting work.

“The resolution of most of these disputes drew on knowledge that was developed as part of previous capability building activities, and on our detailed approach to the associated measurement

which involves multiple repeats and often more than one method of analysis.”

The Government Chemist looked at aflatoxins in melon seeds7 and in peanuts sold as wild bird feed and ochratoxin A in ground black pepper.

For the aflatoxin cases Public Analysts’ findings were upheld and consignments were prevented from entering the food chain.

For the ochratoxin A case, results supported the trader’s laboratory. The scatter between

labs and discussion with the Public Analyst revealed the sample had been difficult to homogenise before division into three - a more likely reason for the divergent results than lab error.

In one honey case, the Trading Standards officer was ultimately satisfied as to the traceability of the product in question and it was withdrawn.

A second honey enquiry was paused pending work by the Joint Research Centre (JRC) and New Zealand authorities.

Future work programme

The Government Chemist will be investing more in developing capabilities in genetic, protein and rapid testing methods for food and agricultural products as part of its programme of work for the period 2017-2020.

“The outputs of this work will not only enable us to respond faster and more flexibly when measurement disputes emerge but will also be disseminated widely with a view to broader adoption by government, and commercial and industrial laboratories​,” added Craston.

Novel molecular methods including Next Generation Sequencing (NGS) will be evaluated and high accuracy digital PCR will be further developed and applied.

Future work will evaluate the accuracy and application of ‘point of use’ technologies to address the emerging concept of ‘the consumer as analyst’ and the use of rapid measurements generated outside a controlled laboratory environment.

Related topics Food safety & quality

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