After a long wait, there’s no longer a weight
A test kit manufacturers perspective
Background: All good things are worth the wait and the weight we lose is strictly speaking a mass … On the 16th November 2018, the world’s increasing demands on measurement, lead to the redefinition of the kilogram (BIPM, 2018). As one of the seven SI base units of quantities (which are used for defining 22 derived units in this internationally agreed system organised by BIPM), the kilogram for mass is now defined in terms of an electric current rather than a physical object – the platinum-iridium ingot held in Paris called “Le Grand K”. After almost 130 years, Le Grand K, as well as six copies held around the world, have been deteriorating with discrepancies between them. The new definition is based on a constant of nature, Planck’s constant, which is more robust and will lead to more precise measurements (Horizon, 2014).
What does it mean for allergen analyses?: For all types of measurements this is an important moment, including for the measurement of the allergen content in foods. A key challenge for robust allergen analysis is the ability to relate results back to a reference. For there to be this essential metrological traceability there needs to be a documented unbroken chain of calibrations, each contributing to the measurement of uncertainty (VIM, 2012), linking back to the reference – in this case, the kilogram, the SI unit of mass.
The benefit of metrological traceability is confidence in the measurement result. This in turn leads to confidence in the implications of the measurement, which for allergen analyses includes: the effectiveness of allergen controls, the levels of cross-contact, the allergen content of a finished product, compliance with a regulatory threshold for gluten. Consequently, this could lead to improvements, for example, in: mandatory & precautionary allergen labelling, allergen information in food service operations, best practice and better protection for the allergic consumer.
The way forward: Currently, when accredited laboratories (ISO17025) perform analyses of a homogenous sample in a proficiency testing round and use different ELISA test kits, submitted results differ. The lack of metrological traceability inherent in the analyses leads to reduced confidence in the accuracy of the results and predictions made from them. The work necessary to address these urgent analytical needs has already been critically reviewed (Walker et al., 2015). The review identified three gaps (production of reference materials, a bioinformatics gap analysis and the development of reference methods) which need to be addressed by the co-ordinated efforts of the allergen analytical community – in particular, through the National Measurement Institutes (e.g. Joint Research Centre of the European Commission) and international collaborations (e.g. MoniQA). These gaps also impact the current work of those involved in standardisation, especially now that there are partnership agreements in place between AOAC/ISO and ISO/CEN. For example, CEN/TC 275/WG12 on Food Allergens is revising technical standards that will provide general considerations and minimum performance criteria for different types of allergen and gluten methods. All these efforts will help to ensure that different methods produce reliable, repeatable and comparable measurement results. Yet to compare results, the units of measurement need to be reported in the same way, preferably expressing the allergenic ingredient protein content and/or by providing a conversion factor. As we start 2019, there needs to be a greater move to adopt SI units which should mean avoiding the use of ‘parts per million’; instead expressing results for example as ‘mg gluten / kg of food’ or a ‘gluten content of 20 mg/kg food’.
Useful source: www.bipm.org