Low Gluten Beers Contain Variable Gluten and Immunogenic Epitope Content

Figures

• 

  Figure 1. The number of proteins detected in each LG beer with DQ core and/or R5 epitopes mapping to them. This reveals the small degree of overlap between R5 and DQ epitopes on the proteins detected in LG beers. All LG beers had between 6 and 9 proteins that contain R5 epitopes, except for LG9.

• 

  Figure 2. The number of distinct peptides detected in chymotryptic samples that contain intact DQ core immunogenic epitopes [48], and additional matches to linear epitopes with confirmed, positive assays filtered for the HLA-DQ alleles characteristic of CD [51] that are nine amino acids or longer. The immunogenic peptides occur on multiple proteins but counted once. Tryptic samples had zero matches to Poaceae antigens. These peptides contain immunogenic epitopes that are not cleaved by trypsin or chymotrypsin, which are incorporated into sample preparation and are also natural intestinal proteases.

• 

  Figure 3. Relative abundance of targeted peptides in control (C) and low gluten (LG) beers, annotated with peptide sequence, gluten protein type, the dataset in which it was measured (trypsin or chymotrypsin), R5 epitope status, and immunogenic epitope status. Intact R5 epitopes are written in bold text. Immunogenic epitopes are underlined, and match epitopes B02, B12, and R15 from Tye-Din et al. (2010) [49], three listed in Sollid et al. (2012) [47], and PQQPFPQPQQPFP, which matched IEDB epitope ID 226653. Cell colors where the peptide was not detected are colored in grey, and others are colored using a white-to-red scale. G-hordeins refer to γ-hordeins.

• 

  Figure 4. Net peak area of monitored hordein and ALP peptides from the (A) tryptic and (B) chymotryptic digested samples across control beers (C1–C4) and low gluten (LG) beers tested. The peak area is an indication of abundance but is not a direct measure of gluten content.

• 

  Figure 5. Tryptic wheat-specific peptides detected in control (C) and LG beers. C2 had an order of magnitude higher wheat content and is shown on a split axis. A single peptide, DVSPGCRPITVSPGTR, was seen in C4, LG3, and LG4 and none were detected in LG9. Multiple peptides were seen at low levels in all other beers.