Effect of screw speed, temperature and moisture on physicochemical properties of corn gluten meal extrudate.

BACKGROUND: Corn gluten meal (CGM) is the main by-product of corn starch with rich protein and dietary fiber. The extrusion of CGM with a twin-screw extruder aimed to expand the novel utilization of this plant-protein resource. The impacts of screw speed, extrusion temperature, and material moisture on physicochemical properties of the extrudates were assessed. RESULTS: The microstructure depicted a favorable fiber-like structure formed under screw speed 120-150 rpm, extrusion temperature 140-150 °C, and material moisture 40-45%. Expansion ratio, rehydration ratio, water solubility index, hardness, and chewiness increased until screw speed reached 120 rpm. With accelerating extrusion temperature, these indicators showed an overall increasing trend. As for material moisture, expansion ratio, hardness, and chewiness showed a decreasing trend. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that disulfide bonds were necessary for protein crosslinking during extrusion. CONCLUSION: It can be concluded that CGM is extrudable, whose textural and physicochemical properties vary as functions of the extruding parameters, providing diversity for its potential applications. © 2023 Society of Chemical Industry.

Physicochemical properties and protein structure of extruded corn gluten meal: Implication of temperature.

Corn gluten meal is a by-product of corn starch production. To extend its application in the food industry, the extrusion of corn gluten meal was conducted, and the effects of temperature (80, 100, 120, and 140 °C) on physicochemical properties and protein structure of the extrudates were investigated. Corn gluten meal was texturized when the extrusion temperature reached 120 °C, and puffed when it reached 140 °C. With an increment of temperature from 120 to 140 °C, the bulk density, particle size, and zeta-potential of extrudates decreased (from 662.0 to 642.5 mg/cm3, 301.0 to 191.3 nm, and 4.82 to 1.52 mV). SDS-PAGE showed that disulfide bonds and other covalent bonds participated in protein cross-linking during extrusion. Thus, a model of temperature factor on protein reaction for texturization was proposed: With increase of extrusion temperature, the protein peptides got more unfolding; more covalent reactions occurred under higher temperature, which could be important for texturization.

Impacts of extrusion temperature and α-subunit content on structure of zein extrudate and viscoelasticity of the plasticized network.

To elucidate the effects of temperature and α-subunit content on the physicochemical characteristics and structure of zein, three zeins (commercial zein, α-subunit-rich zein, and total zein) with high to low α-subunit content were extruded at 80, 100, 120, and 140 °C, respectively. The mechanical properties, peptide distribution, particular size, morphological changes in self-assembly, and intermolecular forces of the extrudates were determined; the extrudates were plasticized by acetic acid, and the rheological properties of the resulted viscoelastic network were measured. With the temperature increase, the solubility of zein extrudates decreased, and the peptide weight of α-subunit-rich zein and total zein increased. Excessive extrusion temperature negatively affected zein's ability to form viscoelastic plasticized networks. Zein with high purity of α-subunit tended to form a fibrous structure. In contrast, the existence of more non-α-subunits (ß-, γ-, and δ-zein) formed a compact one and strengthened the plasticized zein network. Therefore, α-subunit content and extrusion temperature could regulate the structures of zein extrudate or the viscoelasticity of plasticized networks to expand flexible utilization of zein in the food industry.

Application of zein in gluten-free foods: A comprehensive review.

The gluten-free food market is growing worldwide. Zein is a promising gluten substitute in the gluten-free system due to its similar viscoelastic properties to gluten. However, a few existing reviews are limited to the zein characteristics and the application of zein in gluten-free bread and noodles while lacking a comparison of basis information between zein and gluten and the application in other foods, like meat analogue. We compared the structure of zein and gluten at the molecular level to employ zein better in gluten-free food production. The application status of zein in gluten-free systems, the influencing factors of zein functionality, and the potential of zein in meat analogues were summarized comprehensively. The weak elasticity and insufficient gas retention ability are significant challenges for zein dough to produce desired bread. Additives and modifications, such as organic acids and thermal treatment, improve zein functionality by increasing the molecular flexibility or elasticity of the zein network. Future research still needs to focus on increasing zein-starch dough's elasticity and gas retention ability and decreasing zein's high glass transition temperature. Applying zein in meat analogues also requires more attention due to its ability to form fibrous texture.