Gluten replacement and starch reduction in producing gluten free bread

The main target of the project is to investigate gluten replacement and starch replacement in gluten free products for the purpose of dealing with gluten intolerance, obesity, diabetes, and meeting the public requirement of healthy diets. The focus of the first part is on psyllium seed husk powder (PSY), whose main compound is heteroxylan. Both whole PSY and fractions (by temperature) were investigated. Fractions show distinct rheological properties, arabinose/xylose ratios and sidechain substitutions. Two hypotheses were proposed focusing on either chemical and molecular structural properties or hierarchical molecular conformations. Cellulose, fibrillated cellulose (FC) and mixtures with PSY were then investigated. FC suspensions appear as flocculates which can be promoted by either high temperature or distance reduction between fibres. Unheated PSY-FC appears to be binary phase mixture and the rheological property is enhanced with the increase of fibrillation time. The heated mixtures form interpenetrating composites and the treatment on the cellulose surface by fibrillation does not alter the rheological property. However, further fibrillation, which causes significant loss of integrity of the cellulose fibres, enhances the rheological properties and a denser and clumped structure was observed. PSY interacts with cellulose and FC via, possibly, arabinan sidechains, molecular compatibility, or trapping by FC fibres. PSY and methylcellulose (MC) were then applied in the production of gluten free bread based on rice flour. A comprehensive study of the influences of the addition levels of MC, PSY and water on dough rheological properties, proving behaviours, and bread qualities were performed and principal component analysis was applied to understand the correlations between different responses and to reduce the number of data dimensions. Additions of MC and PSY strengthen gluten free doughs but water dilutes the systems and softens the doughs. Dough extensibility is closely correlated with specific volume and can be a good predictor of bread quality. Extensibility can be increased by a coincident increase of hydrocolloid addition, especially MC, and water addition. Appropriate extensibility allows doughs to flow which facilities expansion during proving and generates larger loaves with a less dense crumb and softer texture. Other rheological responses are less significantly correlated to specific volume but sensitive to formulation variations and reflect dough structures and stability. The starch replacement of gluten free bread by cellulose (FC0) and fibrillated cellulose (FC60) was then investigated. Similar to the effects previously reported for hydrocolloids, both FC0 and FC60 decrease pasting temperature due to water and volume competition with starch. Comparing the replacement by either FC0 and FC60, fibrillation increases the functionality of cellulose and enhances the composite structure. They significantly strengthen the doughs due to their high water binding ability and fibrous structure but reduce extensibility. They restrain the volume increase during proving and lead to lower specific volume of loaves with denser and harder crumb. However, the crumb structure is finer. Additionally, the generalised Maxwell model was applied to study the dough rheology. The relaxation frequencies were estimated which are higher than the deformation rate iii during proving. It suggests that gluten free doughs behave like viscoelastic fluid during proving. In summary, gluten free bread with partial replacement of flour can be produced by incorporation of MC, PSY, cellulose and fibrillated cellulose. Deliberate consideration of the addition levels of MC and water would be required to improve bread quality while addition of PSY and flour replacements by cellulose and fibrillated cellulose are detrimental to loaf volume and, therefore, lead to denser and harder crumb. Water addition level needs to be adjusted in further work to improve the bread quality