September 2016

The Government Chemist programme: real-time DNA detection in spices

Food allergies represent a clear threat to the general health and wellbeing of those affected which places increasing pressure on food producers and regulatory authorities.

In 2015, a number of spice products were subject to a costly recall from the international market because of the suspected unlabelled presence of almond, a known allergen from the Prunus genus and an EU listed allergenic species. The Prunus genus contains other ‘stone fruits’ such as apricot, cherry and peach.

These spice samples – cumin and paprika – suspected to be adulterated with almond were referred to the UK Government Chemist in 2015 in its advisory capacity to determine the contaminant. Current techniques, such as immunoassays, typically have difficulties distinguishing between closely related Prunus species as they suffer from cross-reactivity. Using novel DNA-based techniques, scientists from the Government Chemist programme were able to conclusively identify the adulterant species in these samples.

In the case of the cumin, although almond (a known allergen that requires labelling according to the relevant EU Regulation) was initially thought to be the adulterant, later mahaleb, a Mediterranean Prunus species unfamiliar within the UK whose seeds are ground to produce a sweet spice, was suspected. A novel real-time PCR method was developed to definitively determine which species of Prunus was present. The assay was developed based on available DNA sequence information from the Internal Transcribed Spacer (ITS) region, and tested against a variety of species within the Prunus genus to ensure no cross-reactivity. Results confirmed unequivocally that mahaleb DNA was detected in the cumin sample.

In the second study, a commercial paprika sample suspected of having been adulterated with almond was analysed using a novel real-time PCR approach utilising DNA melt analyses. This approach targets the internal transcribed spacer (ITS) sequence to differentiate between a panel of Prunus test species and is capable of discrimination based on the resultant melt profiles. The developed method provides analysts with a simple and broad molecular tool to supplement non-specific ELISA Prunus-positive findings to identify common Prunusspecies for food authenticity and allergen testing purposes.

Malcolm Burns, Principal Scientist for Food Analysis, stated that “These two studies provide demonstrable evidence for the significant role the Government Chemist programme plays in protecting the food chain on behalf of consumers.”

The results of these studies, in which the assays were developed and tested by Gavin Nixon, Senior Researcher, DNA Foods Analysis, under the guidance of Malcom Burns and Michael Walker, have recently been published in two peer-reviewed open access papers.

These papers will be of interest to analytical laboratories involved in trace detection of ingredients in support of relevant food labelling legislation:

Burns M et al, Development of a Real-Time PCR Approach for the Specific Detection of Prunus mahaleb, Food and Nutrition Sciences (2016) 7:703-710, doi: 10.4236/fns.2016.78071

Nixon G et al, Novel Approach to the Rapid Differentiation of Common Prunus Allergen Species by PCR Product Melt Analysis, Food and Nutrition Sciences (2016) 7:920-926, doi: 10.4236/fns.2016.710091