Formation of a viscoelastic dough from isolated total zein (α-, β- and γ-zein) using a glacial acetic acid treatment

A sustainable zein-based adhesive for various substrates with improved adhesion and stability

Biomass-based adhesives are gaining attention as environmentally friendly alternatives to toxic petroleum-based adhesives. However, biomass-based adhesives exhibit poor adhesive properties and are highly susceptible to failure in humid environments. In this study, a zein-based adhesive with high adhesive strength and good water resistance was prepared by optimizing the solvent composition and adding tannic acid. Adding 10 wt% acetic acid to an aqueous ethanol solvent increased the shear strength by 45.4 % to 3.09 MPa. Moreover, the addition of 6 wt% tannic acid improved the shear strength of the zein-based adhesive in humid environments from 0.63 to 1.58 MPa. The tannic acid-reinforced zein-based adhesive exhibited good adhesive strength in both humid and dry environments, which was maintained for 30 days on glass, and could be applied to a wide range of substrates. Moreover, the adhesive showed an antioxidant activity >94 %, excellent thermal stability, biocompatibility, and antibacterial effect. Therefore, this adhesive has great application prospects in medical, packaging, and other fields.

Advances in Extraction, Structure, and Physiochemical Properties of Sorghum Kafirin for Biomaterial Applications: A Review

Kafirin is an endosperm-specific hydrophobic protein found in sorghum grain and the waste by-product from sorghum biorefineries known as sorghum dried distillers' grain with solubles (DDGS). Because of kafirin's poor nutritional profile (negative nitrogen balance, slow digestibility, and lack of some essential amino acids), its direct human use as a food is restricted. Nevertheless, increased focus on biofuel production from sorghum grain has triggered a new wave of research to use sorghum DDGS kafirin as a food-grade protein for biomaterials with diverse applications. These applications result from kafirin's unique chemical nature: high hydrophobicity, evaporation-induced self-assembling capacity, elongated conformation, water insolubility, and low digestibility. Aqueous alcohol mixtures have been widely used for the extraction of kafirin. The composition, structure, extraction methodologies, and physiochemical properties of kafirin, emphasising its biomaterial functionality, are discussed in detail in this review. The literature survey reveals an in-depth understanding of extraction methodologies and their impact on structure functionality, which could assist in formulating materials of kafirin at a commercial scale. Ongoing research continues to explore the potential of kafirin and optimise its utilisation as a functional biomaterial, highlighting its valuable structural and physicochemical properties. Further studies should focus on covering gaps in the research as some of the current structural understanding comes from data on zein protein from maize.

Structure characteristics and physicochemical property of starch, dietary fiber, protein in purple corn flour modified by low temperature impact mill

The structural changes of macromolecules (starch, dietary fiber and protein) in purple corn flour (PCF) modified by a low temperature impact mill (LTIM) at different air classifier speed (ACS) were investigated. LTIM changed the multi-scale structure of starch, which was characterized by increased starch damage, stronger destruction of relative crystallinity (from 37.85 % to 15.53 %) and short-range ordered structure (R_1047/1022, from 1.21 to 0.73) with the increased ACS. The structure of dietary fiber was also destroyed on multi-level, including decreased particle size, destructive morphology, and slightly changed crystalline structure. Additionally, LTIM showed high damage on the senior structure (surface hydrophobicity, disulfide bond, secondary structure) of protein. Due to the structure changes modified by LTIM, starch, dietary fiber and protein played different role on hydration property of PCF. Starch had positive effect, while dietary fiber and protein had negative effect. Our experimental results may provide valuable information for further analysis of other quality changes (oil holding capacity, cation exchange capacity, ability to produce high-quality dough or end-out products, etc.) of purple corn flour after LTIM treatment.

Modification of zein dough functionality using kafirin as a coprotein

Kafirin, sorghum prolamin, was investigated as a coprotein for zein as visco-elastic masses and in starch-based model doughs. Regular kafirin and kafirins from waxy and high protein digestibility (HD) sorghum crosses were studied. HPLC revealed that waxy-HD kafirin was of smaller molecular size and low in β-kafirin. It also had greater surface hydrophobicity. Kafirin addition to zein increased visco-elastic mass elasticity up to ≈50% stress-recovery, similar to wheat gluten. Waxy-HD kafirin gave the highest elasticity, possibly due to its hydrophobicity. Kafirin inclusion at 2:8 parts zein increased the tensile strength of model doughs. Maximum strength was, however, only 60% that of gluten-based dough. Kafirin from regular sorghum gave the highest strength, possibly because of greater disulphide-bonded polymerisation. Confocal laser scanning microscopy showed that zein-kafirin copolymers formed fairly linear fibrils in stretched doughs, indicating excellent compatibility between the proteins. Future research should establish how kafirin-zein copolymer performs in non-wheat flour products.

Vibrational and fluorescence spectroscopy to study gluten and zein interactions in complex dough systems

The volume-spanning network formed by gluten during breadmaking is crucial in the production of high-quality bakery products. Zein proteins are also capable of forming a protein network under specific conditions. Vibrational (Fourier transform infrared spectroscopy (FTIR) and Raman scattering) and fluorescence spectroscopy are powerful, non-invasive techniques capable of assessing protein structures and interactions. The main objective of this project was to explore the suitability of these techniques to study zein and gluten structures and interactions in complex dough systems. The dough samples were prepared by mixing 20 w/w% of protein (with different proportions of zein and gluten) and 80 w/w% of corn starch. The tyrosine (Tyr) fluorescence emission peak (λ_exc = 280 nm) was still present even in those zein-gluten samples containing the highest gluten concentration and lowest zein concentration. This suggests that the Tyr moieties (stemming from zein) are not in close proximity to tryptophan (Trp) of gluten and their fluorescence is not quenched efficiently. Raman scattering results also showed the presence of different Tyr residues, exposed and buried, as well as different conformations of disulfide bridges, in zein and gluten samples. Based on the results from spectroscopic measurements and scanning electron microscopy (SEM), two distinct network structures composed of gluten and zein were identified in the mixed dough systems. The present work illustrates how complementary vibrational (Raman scattering and FTIR) and fluorescence spectroscopy methods can be combined to non-invasively assess protein structure and interactions in a complex food matrix.

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Exploration of non-invasive techniques to study proteins in complex food systems.

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Complementary information obtained on protein structure at several length scales.

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Zein dough viscoelasticity relates to the formation of beta-sheet rich fibrils.

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Gluten and zein form two distinct network structures in dough making.

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Zein inclusion increases water availability for gluten in gluten-zein dough.

Interfacial and emulsion-stabilizing properties of zein nanoparticles: differences among zein fractions (α-, β-, and γ-zein)

According to the solubility in the binary solvent of ethanol water, zein can be classified into α-, β-, γ-, and δ-zein, and the difference in amino acid compositions of these fractions is believed to affect their physicochemical properties and functionalities. This research comparatively analyzed main zein fractions, namely the α-zein fraction, β-zein fraction, and γ-zein fraction, on the formation, surface adsorption, and emulsifying properties of their anti-solvent-induced particles. Results showed that all zein fractions were able to form spherical particles through an anti-solvent procedure, and formed particles possessed different surface charge and surface hydrophobicity. γ-Zein fraction particles had the biggest size and lowest surface hydrophobicity, the highest interfacial adsorption speed, and formed the strongest viscoelastic interfacial film, as analyzed through the interfacial rheology results, while β-zein fraction particles exhibited the poorest interfacial activity. These physicochemical differences were reflected in their emulsifying properties, whereby the γ-zein fraction particle-stabilized emulsion had the maximum tolerance to salt (50, 100, and 200 mM NaCl) and pH (4.0, 7.0, and 9.0). The excellent interfacial properties of the γ-zein fraction presented in this research would afford a new strategy for the effective application of zein.

Factors Influencing Zein-Whole Sorghum Flour Dough Formation and Bread Quality

Zein is known to able to form viscoelastic dough with wheat-like properties under certain conditions. Several studies have been conducted to explain the mechanism behind this ability and to improve the functionality and end-use quality of zein-based dough systems. However, most of this research has been conducted using zein in combination with isolated starches or high-starch flours. To investigate the production of additional zein-whole sorghum flour breads, experiments were conducted to determine factors impacting zein-whole sorghum flour dough and bread quality. Optimizing water levels, using defatted zein and/or sorghum flour, and increasing zein content in dough formulas were investigated as initial formulation steps. Of these factors, increasing zein content from 20% to 30% (flour weight basis) had the greatest impact, resulting in stronger zein-based dough and improved bread quality. Additives and zein treatments shown to impact zein functionality were then investigated for their effect of zein-whole sorghum flour breads. Mixing zein and whole sorghum flour with 0.5% hydrogen peroxide, 5% ethanol, or 3% hydroxypropyl methylcellulose resulted in improved dough strength and bread quality. Breads made from whole white sorghum flour had improved quality compared to zein-based breads made with black or high-tannin whole sorghum flour. PRACTICAL APPLICATION: Zein is known to be able to form wheat-like dough when mixed under the right conditions. Most of the research on zein-based dough and food products has used high-starch flours. This project investigated optimizing the production of zein-whole sorghum flour dough and bread as an alternative. Increasing the zein content in the formula and using additives including ethanol and HPMC produced breads from zein-whole sorghum flour that were like those made with zein and pure starch.