The haze-forming peptides and proteins present in beer mainly originate from the grains used. Such grains, typically barley and wheat, also incorporate gluten. Although partially hydrolyzed during brewing, gluten-containing protein material remains present in the final beers. Gluten-sensitive people might therefore not be able to consume beer without an adverse response. AN-PEP, the proline-specific peptidase in Brewers Clarex, is commercially applied to selectively degrade proline-rich, haze-forming peptides and proteins during beer fermentation. The unusually high percentage of proline in known celiac-related gluten epitopes suggests that they form ideal substrates for AN-PEP as well. We confirmed that in beers prepared with AN-PEP, gluten levels were well below 20 mg/kg based on the established competitive R5 ELISA method. We used a sensitive LC-MS/MS method developed in-house to identify the peptides. Only in beers brewed through a conventional process could we find epitope-containing peptides, even in beers that contained less than 20 mg/kg of gluten based on the ELISA. So even though the MS method is qualitative and not quantitative, it provided a more detailed view of the fate of gluten during brewing. Specifically, these data indicate that AN-PEP is able to degrade all known immunogenic gluten epitopes in beer. We conclude that apart from its current application as a beer stabilizer, AN-PEP has the additional benefit of exhaustive degradation of all potentially problematic gluten epitopes. Keywords: AN-PEP, Brewers Clarex, ELISA, Gluten, Mass spectrometry
Supplementary Table I is an Excel file containing a data set of roughly 31,000 peptide identifications.
Supplementary Table II is an Excel file containing an epitope list incorporating all currently known celiac disease relevant T-cell epitopes.
Supplementary Figure 1 illustrates a situation in which VFLQQQCSPVR was selected as the peptide for selected reaction monitoring quantification.
