Food processing and gluten digestibility: a peptidomic investigation of celiac peptide release

Abstract

This thesis assesses the effect of various food processing techniques on the digestion of gluten within bread. Celiac disease is a T-cell mediated autoimmune disorder precipitated by immunogenic gluten peptides that are resistant to gastrointestinal digestion. One-third of the population has the genetic potential to develop celiac disease, and why an individual loses tolerance to gluten is unknown. Notably, an increasing ‘gluten load’ may contribute. Within wheat dough, gluten proteins assemble into the gluten macropolymer (GMP)—a viscoelastic protein network that is structurally modified during food processing. A protein’s structure can influence its digestibility; this relationship is protein-specific and poorly understood. This thesis used mass spectrometry (MS) to determine if the GMP’s structure can influence protein digestibility and the release of immunogenic gluten peptides. A label-free targeted MS method was developed to quantify six marker immunogenic peptides within a model food matrix. Bread was digested using the INFOGEST in vitro digestion assay, then targeted and discovery MS were used to identify 82 immunogenic gluten peptides and quantify the marker peptide release profiles. Within wheat bread, gluten’s structure and digestibility were investigated in response to five food processing techniques; specifically, mixing, baking, sourdough fermentation, protein glutaminase and microbial transglutaminase. Structural changes to the GMP were detected by confocal laser scanning microscopy, protein network analysis, extractability and free sulfhydryl assays. Each processing condition altered different aspects of the GMP’s structure. Targeted MS showed that baking and sourdough fermentation altered the in vitro peptide release profile. MS revealed neither protein glutaminase nor microbial transglutaminase (0-2000 U kg-1) deamidated immunogenic gluten within a dough system. The in vivo implications of these findings are unclear and should be further investigated. MS proved a powerful tool to study the digestion of gluten, revealing complex and previously unknown in vitro digestion profiles and trends. The in vitro digestion trends and peptide concentrations calculated during this research can be applied to other experimental systems to improve their design. Overall, mixing, microbial transglutaminase, baking temperature and time did not alter the immunogenic peptide release profile, and thus, are unlikely to influence the gluten load of bread.