Because of coeliac disease, some individuals cannot tolerate the protein gliadin present in the gluten fraction of wheat flour. From a commercial perspective, there is a need for the development of gluten-free bread with texture and flavour properties similar to the conventional wheat flour loaf. In the context of bread, the gluten component of wheat has a crucial role in stabilising the gas-cell structure and maintaining the rheological properties of the bread. The absence of gluten results in liquid batter rather than pre-baking dough, yielding baked bread with a crumbling texture, poor colour and other post-baking quality defects. The liquid batter cannot be processed on the existing production line of baking industry. The aim is to develop a gluten-free white loaf with similar quality characteristics to that of standard white bread on the existing processing lines at Quality Bakers New Zealand. Within this constraint, dough has to be produced with handling and moulding properties similar to those of conventional wheat flour loaves. This research focused on finding and implementing the gluten substitutes for the development of gluten-free high quality commercial bread. In this research, the independent variables were conventional wheat flour (the most basic control), other gluten-free flours from a variety of sources, starches, supplementary proteins, hydrocolloids such as hydroxypropylmethylcellulose (HPMC), hydrophilic psyllium husk, and enzymes such as microbial transglutaminase, glucose oxidase, lipase and fungal α-amylase. These ingredients were trialled in different combination and composition to produce a dough having ability to trap the carbon dioxide gas during proofing and baking to get high specific volume bread suitable for the Quality Bakers’ product range. After an essentially ‘shotgun’ approach to formulations, the research narrowed to a systematic and progressive variation of ingredients and their composition to develop workable commercial models. Ingredients and their compositions were manipulated according to the outcomes of the trials and their contribution in the formulations. The dependent variables included standard bakery rheological properties based on dough stickiness, dough extensibility, oven spring, bread specific volume, bread slice ability, and bread staling. A gelation system of the lower-temperature-stable hydrocolloid psyllium husk, the heat-stable hydrocolloid hydroxypropylmethylcellulose, maize starch, and potato starch was created to form industrial process able dough having ability to entrap carbon dioxide gas produced during proofing and initial phase of baking. Microbial transglutaminase was used to increase the cross linking of protein present in flours and supplemented for enhancing the dough-like structure and its gas entrapping abilities. A formulation has been discovered by this research for the development of high quality gluten-free commercial bread. The formulated bread has similar quality characteristics to that of standard white bread and can be produced on existing processing lines at Quality Bakers. Industrial process able gluten-free bread with similar quality characteristics to that of standard white bread can be formulated by using a specific combination of soy flour, maize starch, potato starch, yoghurt powder, milk protein, HPMC (K4M), psyllium husk, microbial transglutaminase, lipase, and fungal α-amylase. The significance of this research is mainly commercial and the insights gained may extend to other bakery items that could be used by coeliacs.

Because of coeliac disease, some individuals cannot tolerate the protein gliadin present in the gluten fraction of wheat flour. From a commercial perspective, there is a need for the development of gluten-free bread with texture and flavour properties similar to the conventional wheat flour loaf. In the context of bread, the gluten component of wheat has a crucial role in stabilising the gas-cell structure and maintaining the rheological properties of the bread. The absence of gluten results in liquid batter rather than pre-baking dough, yielding baked bread with a crumbling texture, poor colour and other post-baking quality defects. The liquid batter cannot be processed on the existing production line of baking industry. The aim is to develop a gluten-free white loaf with similar quality characteristics to that of standard white bread on the existing processing lines at Quality Bakers New Zealand. Within this constraint, dough has to be produced with handling and moulding properties similar to those of conventional wheat flour loaves. This research focused on finding and implementing the gluten substitutes for the development of gluten-free high quality commercial bread. In this research, the independent variables were conventional wheat flour (the most basic control), other gluten-free flours from a variety of sources, starches, supplementary proteins, hydrocolloids such as hydroxypropylmethylcellulose (HPMC), hydrophilic psyllium husk, and enzymes such as microbial transglutaminase, glucose oxidase, lipase and fungal α-amylase. These ingredients were trialled in different combination and composition to produce a dough having ability to trap the carbon dioxide gas during proofing and baking to get high specific volume bread suitable for the Quality Bakers’ product range. After an essentially ‘shotgun’ approach to formulations, the research narrowed to a systematic and progressive variation of ingredients and their composition to develop workable commercial models. Ingredients and their compositions were manipulated according to the outcomes of the trials and their contribution in the formulations. The dependent variables included standard bakery rheological properties based on dough stickiness, dough extensibility, oven spring, bread specific volume, bread slice ability, and bread staling. A gelation system of the lower-temperature-stable hydrocolloid psyllium husk, the heat-stable hydrocolloid hydroxypropylmethylcellulose, maize starch, and potato starch was created to form industrial process able dough having ability to entrap carbon dioxide gas produced during proofing and initial phase of baking. Microbial transglutaminase was used to increase the cross linking of protein present in flours and supplemented for enhancing the dough-like structure and its gas entrapping abilities. A formulation has been discovered by this research for the development of high quality gluten-free commercial bread. The formulated bread has similar quality characteristics to that of standard white bread and can be produced on existing processing lines at Quality Bakers. Industrial process able gluten-free bread with similar quality characteristics to that of standard white bread can be formulated by using a specific combination of soy flour, maize starch, potato starch, yoghurt powder, milk protein, HPMC (K4M), psyllium husk, microbial transglutaminase, lipase, and fungal α-amylase. The significance of this research is mainly commercial and the insights gained may extend to other bakery items that could be used by coeliacs.

The gluten-free diet is the only treatment available for gluten-related disorders, such as celiac disease, an autoimmune reaction to gluten, or non-celiac gluten or wheat sensitivity, a symptomatic reaction to wheat or gluten. However, gluten may not be the only culprit, and patients on a gluten-free diet have been suggested to symptomatically improve through the placebo effect, alterations in immune activity, and alterations in gut microbiota composition. It is unclear which of these mechanisms underlie symptoms in gluten-related disorders and well-designed clinical studies are needed to better understand them. This thesis aims to understand the mechanisms and symptomatic responses by which wheat and gluten affect individuals with gluten-related disorders. I hypothesize that patients with gluten-related disorders have increased psychological symptoms and immune reactivity which may be modulated by the gut microbiota. To test this, I conducted a clinical crossover trial to investigate whether whole wheat or gluten triggered symptoms versus gluten-free control, or nocebo, in irritable bowel syndrome patients adopting a gluten-free diet. Participants reacted similarly to each intervention, suggesting a strong 'nocebo effect' to be the main trigger of their symptoms. However, several participants did not comply to the protocol, muddying the results. Subsequent follow-up visits after disclosing personalized study results found no changes in participant beliefs, behaviours, and symptoms, and most remained on a gluten-free diet. Next, a systematic review of 65 observational studies found an elevated risk of IBD in celiac disease and vice versa. Finally, a systematic review of 6 RCTs found limited evidence that probiotics are safe and possibly therapeutic for ameliorating symptoms in celiac disease. Overall, the work presented in this thesis critically assesses the mechanisms by which gluten and wheat trigger symptoms in gluten-related disorders and highlights the importance of rigorous clinical trial design to control for psychological factors and patient compliance. / Thesis / Doctor of Philosophy (PhD) / Gluten, a wheat protein, is commonly associated with the autoimmune condition celiac disease, symptomatic worsening from gluten or wheat in non-celiac gluten/wheat sensitivity, and irritable bowel syndrome. This thesis strove to understand how gluten and other wheat proteins impact symptoms via psychological, immune, and/or bacteria-mediated pathways in gluten-related disorders. A clinical trial tested the effects of whole wheat, gluten, and gluten-free control on symptoms in irritable bowel syndrome patients on a gluten-free diet. We found no differences between interventions but discovered widespread diet non-compliance and that patient fears triggered symptoms. Informing patients of whether wheat, gluten, or gluten-free control triggered their symptoms did not change their dietary beliefs or behaviours. Additionally, two systematic reviews found a relationship between celiac disease and inflammatory bowel disease, and a possible therapeutic effect of probiotics in celiac patients. Our findings provided insights into the content and quality of the clinical evidence for gluten-related disorders.