Film-forming properties and mechanisms of soy protein: Insights from ß-conglycinin and glycinin.

Extensive research has been conducted on soy protein films; however, limited information is available regarding the influence of the major components, ß-conglycinin (7S) and glycinin (11S), on the film-forming properties of soy protein. This study aimed to isolate the 7S and 11S fractions in order to prepare films and investigate the impact of varying 7S/11S ratios on the film-forming solutions (FFS) and film properties. The findings revealed that higher 11S ratios led to increased protein aggregation, consequently elevating the storage modulus (G') of the FFS. Notably, an optimal 7S/11S ratio of 7S1:11S2 (CF3) significantly enhanced the film's water resistance. Specifically, it enhanced the water contact angle by an impressive 17.44 % and reduced the water vapor transmission rate by 27.56 %. These improvements were attributed to intermolecular interactions, involving hydrogen bonds and salt bridges, between the amino acid residues of 7S and 11S. As a result, a more uniform and dense microstructure was achieved. Interestingly, the mechanical and optical properties of the film were maintained by the different protein fractions examined. In summary, this study contributes to the understanding of the film-forming properties of soy protein, particularly the role of 7S and 11S.

Breaking the temperature limitation of zein-rice starch dough by microwave pre-gelatinization: Morphological, structural and rheological properties of the dough.

Zein has gluten-like viscoelasticity, but its use is limited due to high glass transition temperature (Tg). 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 Tg, which provided a safe and effective way to break the temperature limitation of zein as a structural protein used in foods.

Influence of pH and ionic strength on the physicochemical and structural properties of soybean ß-conglycinin subunits in aqueous dispersions.

Understanding the impact of pH and ionic strength on the physicochemical and structural properties of soy proteins at subunit level is essential for design and fabrication of many plant-based foods. In this study, soybean ß-conglycinin and its subunit fractions αα' and ß were dispersed in solutions with different pH values (3.7, 7.6, and 9.0) at low (5 mM NaCl) and high (400 mM NaCl) ionic strengths, respectively. The solubility, rheology, particle size, zeta potential, microstructure, secondary structure, and tertiary structure of the different dispersions were analyzed using a range of analytical methods. The ß-conglycinin, αα'- and ß-subunits aggregated near the isoelectric point (pH 3.7). Increasing the ionic strength led to the assembly of more homogeneous units. An increase in ionic strength at pH 7.6 and pH 9.0 led to electrostatic screening, which promoted dissociation of the aggregates. The ß-subunit showed a greater sensitivity to pH and ionic strength than the αα'-subunits. Based on the evidence from a range of analytical methods, the highly hydrophilic extension region of the αα'-subunits played an important role in determining the stability of the ß-conglycinin dispersions under different environmental conditions. Moreover, the N-linked glycans appeared to impact the conformation and aggregation state of the ß-conglycinin.

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.

Heat-induced aggregation of subunits/polypeptides of soybean protein: Structural and physicochemical properties.

To reveal the nature of thermal aggregation of soybean protein at subunit level, structure and physicochemical properties of αα'- and ß-subunits isolated from ß-conglycinin, acidic polypeptide, and basic polypeptide from glycinin, as well as ß-conglycinin and glycinin, were characterized before and after heat treatment. The transmission electron microscopy (TEM) images showed that ß-conglycinin, αα'-subunits and acidic polypeptide formed regular thermal aggregates, which exhibited high solubility, high ζ-potential value, and small particle size. While glycinin, ß-subunit, and basic polypeptide aggregated to insoluble clusters with large particle size distribution. The results of size exclusion chromatography and non-reducing electrophoresis showed that the disulfide bond was the important force in stabilizing the protein conformation of thermal aggregates in ß-conglycinin, glycinin, and their isolated subunits/polypeptides but ß-subunit. The results of surface hydrophobicity and intrinsic fluorescence spectra showed that the thermal aggregations of ß-subunit and basic polypeptide were mainly driven by hydrophobic interactions.

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.

The role of the extension region on the structural and physicochemical characteristics of the α-subunit of ß-conglycinin: implications of pH value and ionic strength.

BACKGROUND: To clarify the role of the extension region on the structure-functional relationship of the α-subunit of ß-conglycinin, α-subunit and its segment of the core region (αc-subunit) were expressed via an Escherichia coli system. Their physicochemical properties were compared under acid, neutral or alkaline conditions (pH 4.0, 7.0, and 8.0) and high or low ionic strength (µ = 0.05 and 0.5), respectively. RESULTS: The results showed that the extension region contributed to increasing thermal stability, especially at low ionic strength under acidic and neutral conditions. The extension region stabilized the α-subunit with high solubility, low turbidity, and small particle size under neutral and alkaline conditions, whereas these impacts were suppressed at a high ionic strength and acidic conditions. Surface hydrophobicity of the α-subunit decreased under acidic and alkaline conditions without being interfered with by ionic strength. CONCLUSION: It can be concluded that the extension region played different roles under different pH and ionic strength conditions. These factors should be specified carefully and speculated individually to explore the more detailed and profound nature of ß-conglycinin at the submolecular level. The results could benefit a better understanding of the relationship between domain structure and functions of soybean protein. © 2022 Society of Chemical Industry.

Effect of potato flour on quality and staling properties of wheat-potato flour bread.

To elucidate the impact of potato flour (PF) on quality changes and staling characteristics of the composite bread from wheat-potato flour (WPF), the physicochemical (specific volume, colority, sensory value, texture, and viscosity) properties, and staling (X-ray diffraction and water migration) properties of bread were investigated. The quality of composite bread was comparable to wheat bread when addition level of PF at 20%, but decreased when the addition level increased to 30% or more, and became unacceptable at 50%. A chewy mouthfeel and an elastic and none-crumbly texture were observed on composite bread, which had higher hardness than wheat bread, and could keep on both longer linear distance and higher linear force during compression test. It indicated that such new parameters other than hardness should be introduced to coordinate with the texture quality of composite bread. During storage, the higher addition level of PF significantly decreased crystallinity of composite bread and slowed water migration rate from the crumb to crust, suggesting that PF had antistaling effect on composite bread, which was further emphasized by the fact that the setback value of the WPF decreased with the increase of PF addition.

The effects of extruded corn flour on rheological properties of wheat-based composite dough and the bread quality.

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.