New analytical method for testing gluten-free beer assessed

A study examining gluten-free testing methods in Germany found that some barley beers labelled as ‘gluten-free’ contained small amounts of gluten residues which standard antibody-based tests didn’t detect. The researchers at Leibniz Institute for Food Systems Biology at the Technical University of Munich compared two antibody-based testing methods with a mass spectrometric detection method that they have developed.

According to the international guidelines of the Codex Alimentarius, a food in the EU is officially considered ‘gluten-free’ if its gluten concentration is no more than 20 mg/kg. However, there are stricter rules in Australia and New Zealand. Under Standard 1.2.7 of the Australia New Zealand Food Standards Code (the Code) foods labelled ‘gluten-free’ must have no detectable gluten (generally <3 to <5 parts per million), while ‘low-gluten’ foods must stay below 20 ppm.

The research team in Germany, with principal investigator Katharina Scherf and first author Eleonora Tissen, examined four beers containing gluten and 21 gluten-free barley beers. In addition to two established ELISA methods, the researchers used a newly developed method of nano-liquid chromatography-tandem mass spectrometry (nanoLC-MS/MS), which is designed to specifically identify coeliac disease-active peptides.

The study results showed differences between the three different detection methods: for example, the G12-ELISA confirmed gluten concentrations below 20 milligrams per kilogram in all beers labelled as gluten-free. The R5-ELISA, on the other hand, detected concentrations in four of these beers that slightly exceeded the EU limit. Using the mass spectrometry method, the team also identified a total of 44 peptides that, according to the literature, can trigger coeliac disease due to their molecular structure, 29 of which were found in gluten-free labelled beers. Seventeen of the 44 coeliac-active peptides had a structure that the ELISA antibodies currently in use cannot detect, according to the researchers.

“Our results mean that gluten-free barley beers are generally safe. However, they also show that there can be discrepancies between antibody tests and that they do not detect all coeliac-active peptides known from the literature,” said Tissen, who completed her doctoral studies in Scherf’s research group. Scherf added: “Whether the peptides we additionally identified actually trigger health-relevant reactions cannot yet be conclusively assessed. The good news is that their concentrations were very low and below the EU limit.”

According to the researchers, further investigations are needed. “In the long term, the combination of established rapid tests and modern mass spectrometry methods could make gluten-free foods even safer. In any case, our study is already providing important impetus for the further development of analytical methods,” said Scherf, who heads the research group Food Biopolymer Chemistry at the Leibniz Institute.

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