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The effects of extruded corn flour (ECF) on the rheological properties of the wheat‐based composite dough and quality of the bread were investigated. The RVA results of the composite flour with ECF showed weak thermal viscosity and resistance to starch retrogradation. Mixolab tests revealed that the water absorption capacity increased with the increasing amount of ECF, while dough development time (DT) and dough stability (ST) showed a downward trend, and the composite dough became more resistant to retrogradation. The microstructure of the composite dough showed that the presence of both ECF and unextruded corn flour (UECF) resulted in a more broken gluten matrix. The breads made from the composite flour with ECF had significantly softer texture, lower hardening percentage with storage time, darker crust color, larger specific volume, and higher sensory scores than the UECF ones. It is concluded that the extrusion of corn flour is an effective way to improve the quality of the composite bread and retard staling during storage. [ABSTRACT FROM AUTHOR]

Summary: Addition of raw black rice flour leads to deficient processability on bread making quality. One of the effective methods to modify the functional properties of black rice flour (BRF) composite dough is to extrude black rice flour (EBRF) before incorporation. This study investigated and compared the effect of BRF and EBRF addition level of 10%–50% on the rheology, microstructure of dough and bread quality. The rheological properties of composite dough were recorded by Mixolab, stress relaxation and tensile test. The substitution of EBRF presented higher water absorption but lower development time, protein weakening, starch gelatinization, starch gel stability and starch retrogradation than wheat flour dough. Both the BRF and EBRF dough presented solid‐like behaviour, while the EBRF dough showed more viscous, higher resistance and extensibility than BRF dough. The dough microstructure of dough was observed by SEM, and a more compact structure of EBRF dough could be seen than BRF dough. The incorporation of EBRF in bread quality presented higher specific volume, lower bake loss and firmness than BRF bread. These findings indicated the potential utilisation value of extruded black rice flour in bread making. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ethanol-plasticization enhanced the hydrophobic interactions of zein. • Ethanol-plasticization promoted the formation of fibrous structure of zein-starch dough. • The dense structure of extruded zein prevented the permeation of ethanol. • The structural improvement on extruded zein-starch dough was limited. To improve the viscoelasticity of zein in gluten-free dough, ethanol-plasticization and extrusion modification were employed. The peak viscosity of UZS (unextruded zein-starch) flour and EZS (extruded zein-starch) flour with ethanol (10 %, v/v) increased from 1340.0 to 1996.5 mPa·s and 1336.3 to 2291.5 mPa·s, and the bound bromophenol blue increased from 7.1 μg to 10.6 μg and 5.3 μg to 5.9 μg, respectively. Ethanol-plasticization enhanced zein's hydrophobic interactions and promoted zein network development, thus improving dough compatibility. However, the dense structure of the extruded zein made ethanol inaccessible to the interior, and the structural improvement on extruded zein-starch dough was limited. A model was developed to explain the influences of extrusion and ethanol-plasticization on the behavior of zein in the dough. Extrusion reduces the fiber-forming ability of zein, while ethanol-plasticization facilitates extensive fibrous network formation. This study provides a sound basis for the development of zein in gluten-free foods. [ABSTRACT FROM AUTHOR]

[Display omitted] • Microwave pre-gelatinized zein-starch dough maintained viscoelasticity below zein's T g. • Zein improved starch dough with a smooth surface and compact structure. • Unextruded zein formed fine fiber and was uniformly distributed in the starch base. • Extruded zein tended to present as protein lumps in the starch base. Zein has gluten-like viscoelasticity, but its use is limited due to high glass transition temperature (T g). To break the temperature limitation of zein-starch dough, microwave heating was used to pre-gelatinize a partial of the starch with zein, and then the remaining was added and kneaded to form a dough. Pre-gelatinized doughs formed by rice starch (PRS), zein-starch (PUZS), and extruded zein-starch (PEZS) were included in this study. The thermal, morphological, rheological, and secondary structural properties of the dough were investigated. The results showed that zein and starch formed a composite gel network and firmly bound starch granules, which improved the dough properties with a smooth surface and compact internal structure, increased strain tolerance, and decreased stiffness. Unextruded zein was distributed uniformly and had strong interactions with the starch. Extruded zein tended to form large particles and had limited interaction with starch but improved dough extensibility. Microwave pre-gelatinization increased the stability of the secondary structure of zein and maintained the viscoelasticity of dough below zein's T g , which provided a safe and effective way to break the temperature limitation of zein as a structural protein used in foods. [ABSTRACT FROM AUTHOR]

Zein forms viscoelastic network with water to support the weak structure of gluten-free dough, but which requires temperature above 40 °C. A new method preparing zein network at room temperature using food-grade acetic acid was reported in our previous research. The current research explored the influence of zein network containing acetic acid on the rheology, texture, and tensile properties of rice gluten-free dough, as well as the interaction between zein network and rice flour. Results showed that zein network could act as a structural support material by binding rice flour particles to transmit its viscoelasticity and extensibility to rice dough, thus enhancing the ability of rice dough to resist external forces. The structural characteristics of zein-rice dough were both zein network-dependent and rice flour-dependent. α-Zein network could mix with rice flour particles more evenly than total-zein (T-zein, comprising α-, β- and γ-zein) network due to the thinner and denser fiber bundles, so the stretchability and thermal stability of α-zein-rice dough were greater than that of T-zein-rice dough, and the cooking loss of α-zein-rice noodle was less than that of T-zein-rice noodle. Compared with japonica rice dough and indica rice, waxy rice had less amylose, so the elasticity of zein-waxy dough was weaker than that of zein-japonica dough and zein-indica dough. And the gel network formed by amylose in rice during heating increased the elasticity of zein-rice dough. Additionally, the interaction between zein network and rice flour increased the ordered structure of starch in rice flour. [Display omitted] • Zein network increased the ordered structure of starch in rice flours. • Zein network could improve the structural defects of rice dough. • Zein network increased the viscosity and decreases the elasticity of rice dough. • Zein network could give the rice gluten-free dough with extensibility. [ABSTRACT FROM AUTHOR]