Microstructural characterisation and glycemic index evaluation of pita bread enriched with chia mucilage

Chia seeds can be considered a functional food due to its soluble fibre (mucilage) that could be used to reduce the glycemic index in bakery products. Hence, the aim of this work was to evaluate the effect of chia mucilage on the structure of a flat bread (crumb and crust) and its relation to in-vitro glycemic index. Bread structure was evaluated by scanning electron (SEM), and confocal laser scanning microscopies. X-ray diffraction analysis and differential scanning calorimetry were also carried out. Results showed that the addition of fibre promoted changes in the starch structure, the crumb of all samples presenting the smallest X-ray diffraction peaks, higher gelatinisation degrees (100%), and both, amylose-lipid and B-type structures. Regarding the crust, it presented an A-type diffraction pattern and the least gelatinisation degree (48.75%). With respect to the glycemic index (eGI), different values were obtained depending on the section of the sample. In the crust, control bread presented higher values (73.2 ± 1.7, 69.4 ± 1.2%) than mucilage added bread (69.5 ± 1.9, 66.3 ± 0.7), while in the crumb section and for the whole bread, the eGI was higher for breads added with fibre (71.8 ± 1.1%, 70.0 ± 2.0%, 73.1 ± 0.42%). Gelatinisation enthalpy values from DSC, and SEM and confocal micrographs reinforced the eGI results. From this study it can be concluded that the presence of fibre on flat bread affects the degree of gelatinisation and the eGI, with the crumb of the bread having larger values; while at the crust, a portion of starch granules remained in their native state.