Extensional flow, viscoelasticity and baking performance of gluten-free zein-starch doughs supplemented with hydrocolloids

Viscoelastic doughs of zein and starch were prepared at 40 degrees C, above the glass transition temperature of zein. The effects of hydrocolloid supplementation with hydroxypropyl methylcellulose (HPMC) or oat bran with a high content of beta-glucan (28%) were investigated by dynamic measurements in shear, confocal laser scanning microscopy (CLSM) and Hyperbolic Contraction Flow. Zein-starch dough without hydrocolloids exhibited rapid age-related stiffening, believed to be caused by cross-links between peptide chains. A prolonged softness was attributed to doughs containing hydrocolloids, with the oat bran exhibiting the most pronounced reduction in age-related stiffening. Moreover, CLSM-images of dough microstructure revealed that a finer fibre network may be formed by increased shearing through an addition of viscosity-increasing hydrocolloids, a reduction in water content in the dough or the use of appropriate mixing equipment. The Hyperbolic Contraction Flow measurements showed that doughs containing hydrocolloids had high extensional viscosities and strain hardening, suggesting appropriate rheological properties for bread making. Zein-starch dough without hydrocolloids showed poor bread making performance while hydrocolloid additions significantly improved bread volume and height. Although the hydrocolloid supplemented doughs had similar extensional rheological properties and microstructures, a fine crumb structure was attributed only to bread containing HPMC, marking the importance of surface active components in the liquid-gas interface of dough bubble walls. Zein could not mimic the properties of gluten on its own, but hydrocolloids did positively affect the structural and rheological properties of zein, which yielded dough similar to wheat dough and bread with increased volume