Interactions between wheat starch, hydroxypropyl methyl-cellulose (HPMC) and psyllium seed husk in gluten-free breadmaking

Hydroxypropyl methylcellulose (HPMC) and psyllium seed husk (PSH) have been described as possible network forming components in gluten-free bread. However, there is still a lack of knowledge about their functionality in gluten-free breadmaking. In this study, the interactions between HPMC and PSH in a gluten-free model system with wheat starch were studied. Their functionality was investigated through rheology, cryo-scanning electron microscopy (cryo-SEM) and baking trials. First, the rheological properties and microstructure of the individual hydrocolloid solutions were investigated. Next, their interactions with starch were studied by pasting experiments at different incorporation levels (2.5-5-7.5-10 %) and different HPMC/PSH ratios (0:100, 25:75, 50:50, 75:25, 100:0). Cryo-SEM images of the paste were also obtained at different stages during the pasting experiment. Lastly, baking trials were performed at two levels of dough consistency and the effect of HPMC and PSH on bread quality was assessed. Solutions of HPMC as well as of PSH showed Newtonian or shear-thinning behaviour, depending on their concentration, whereas hysteresis was only observed for PSH. Oscillatory shear experiments showed that thermal gelation of HPMC and melting of the weak PSH gel occurred around the same temperature. The pasting experiments indicated that HPMC especially impacted the start of gelatinisation and retrogradation whereas PSH contributed more to the overall viscosity of the paste especially at high concentration. HPMC largely contributed to air retention during fermentation and baking. A higher amount of psyllium in the dough formulation exhibited a negative effect on bread quality parameters. The optimal combination of HPMC and PSH depended on the dough consistency