Detection of gluten in a pilot-scale barley-based beer produced with and without a prolyl endopeptidase enzyme

ABSTRACT

Immunochemical and mass spectrometric methods were used to examine the gluten composition of a gluten-reduced beer produced by brewing with barley malt in the presence of prolyl endopeptidase (PEP) and a final filtration treatment with diatomaceous earth and perlite. The competitive ELISA is generally considered appropriate for the analysis of hydrolysed gluten, but it is not considered a scientifically valid method for the quantification of gluten in fermented or hydrolysed foods due to the lack of an appropriate reference standard. As no single analytical method can capture the spectrum of gluten-derived products in beer, a comprehensive approach was employed to analyse the intact and hydrolysed fractions of gluten with complementary methods. The combination of PEP addition and diatomaceous earth/perlite filtration was more effective at reducing the concentration of detectable gluten than each of the treatments alone. However, gluten proteins and/or polypeptides were observed in filtered, PEP-treated beers using sandwich ELISA methods, western blot, and bottom-up mass spectrometry. In addition, mass spectrometry results showed that the number of hydrolysed gluten peptides was almost unaffected by the filtration process. Gluten peptides that contained potentially immunopathogenic sequences were identified in the filtered PEP-containing beers by MS. Variability in gluten composition was observed between three replicate pilot-scale productions, suggesting that the gluten profile in beer could differ from batch to batch. As there is uncertainty in the detection and quantification of gluten in hydrolysed and fermented foods, characterisation of hydrolysed gluten by complementary analytical methodologies is recommended.

Graphical Abstract

KEYWORDS:

• Hydrolysed gluten
• PEP
• filtration
• quantification
• mass spectrometry
• immunopathogenic sequence
• celiac disease
• hordein
• gluten-reduced; fermentation

Acknowledgments

Appreciation is expressed for the technical support provided by UW-Madison for their work in producing the pilot plant beer used in this study. The authors also acknowledge the assistance provided by Joe Casey (Craft Brewers Alliance) and Sylvie van Zandycke (Lallemand) for input in the conditions used in the brewing trials. The authors would also like to thank James Pettengill for writing custom Python scripts that were used to analyse the MS results. This project was supported by the U.S. Food and Drug Administration (FDA) and the Institute for Food Safety and Health (IFSH). This project was also supported in part by an appointment to the Research Participation Program at CFSAN administered by ORISE through an interagency agreement between the U.S. DOE and the U.S. FDA.

Disclosure Statement

No potential conflict of interest was reported by the authors.

Supplementary material

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