Environmental parameters-dependent self-assembling behaviors of α-zein in aqueous ethanol solution studied by atomic force microscopy

Self-Assembly Behavior of Zein on Two Different Substrates Visualized by Atomic Force Microscopy

When protein molecules come into contact with different types of substrate materials, the surface properties of the substrate will have a significant effect on their self-assembly behavior. The purpose of this study was to investigate the self-assembly behavior of zein molecules on the two different substrates. Herein, the microstructure of zein molecules on the surface of two typical substrates, mica and glass, were characterized in detail by atomic force microscopy. It was found that zein molecules self-assemble to form spherical structures with uniform size and close arrangement on mica substrates. Compared with mica, the rough glass surface possesses a larger water contact angle, which leads to weaker interaction between zein molecules and its surface, thus enhancing the interaction between zein molecules. Therefore, the zein molecules on the glass substrate exhibit a distinct hierarchical arrangement of one large globule surrounded by many smaller ones. This work provides valuable information for further study of the self-assembly behavior of zein molecules on the substrate surface.

Plant-based protein amyloid fibrils: Origins, formation, extraction, applications, and safety

Amyloid fibrils (AFs) are highly ordered nanostructures formed through the self-assembly of proteins under specific conditions. Due to their unique properties, AFs have garnered significant attention as biomaterials over the past decade. Nevertheless, the increasing reliance on animal proteins for AFs production raises sustainability concerns, highlighting the need for a transition to plant-based proteins as more environmentally friendly feedstocks. This review summarizes the conditions, mechanisms, and factors influencing the fibrillisation of over 20 plant-based protein amyloid fibrils (PAFs). The effectiveness of enzymatic extraction and membrane separation for isolating PAFs was also evaluated. Additionally, the review discusses the potential for enhancing PAFs' suitability through cross-linking with external agents. In the future, PAFs may be developed as advanced nanomaterials for a range of applications, including food hydrogels, cell-cultured meat scaffolds, and food detection sensors. However, thorough investigation of safety concerns and process improvements remain the primary challenges for the development of PAFs.

Genipin-enriched chitosan-Zein nanoparticles for improved curcumin encapsulation

Polysaccharide-protein nanocomplexes are considered one of the desired systems to encapsulate bioactive compounds. The study prepared chitosan (CS)/genipin (GP)/zein nanoparticles with chemical cross-linkage for encapsulating and releasing curcumin. Fourier transform infrared spectra demonstrated that cross-linkage between molecules was attributed to electrostatic interactions and the formation of amido bonds and hydrogen bonding. Transmission electron microscopy showed that all prepared nanoparticles showed a spherical morphology. Particularly, cinnamaldehyde screening -NH2 groups in CS significantly reduced the encapsulation efficiency of nanoparticles, demonstrating the significant role of the -NH2 group in CS-coated zein nanoparticles. Additionally, the encapsulation efficiency was largely increased to 82.3 % at the ratio of CS/GP/zein (w/w, 20:1:100), compared with 38.4 % using zein as a single encapsulation for curcumin. In vitro digestion, the addition of GP and CS decreased the release of curcumin from 84.8 % to 57.1 % after the initial digestion of 2 h. The GP/CS/zein particles retained 12 % of curcumin after 6- h of digestion, indicating the improvements in encapsulation efficiency and release properties.

Improvement of mechanical, barrier properties, and water resistance of konjac glucomannan/curdlan film by zein addition and the coating for cherry tomato preservation

The mechanical, barrier properties, and water resistance of packaging materials are crucial for the preservation of fruits and vegetables. In this study, zein was incorporated as a hydrophobic substance into the konjac glucomannan (KGM)/curdlan (KC) system. The KC/zein (KCZ) showed good compatibility with the zein aggregates uniformly distributed in the network formed by an entanglement of KGM and curdlan micelles based on hydrogen bonds. The presence of zein inhibited the extension of the KC entangled structure and enhanced the solid-like behavior. The high content of zein (>6 %) increased zein aggregation and negatively affected the structure and properties of KCZ. The zein addition significantly improved the water vapor permeability, tensile strength, and elongation at break. The hydrophobicity of the KCZ films was significantly enhanced, accompanied by the water contact angle increasing from 81° to 112°, and the moisture content, swelling, and soluble solid loss ratio decreasing apparently. The K56C40Z4 coating exhibited an excellent preservation effect to inhibit the respiration of cherry tomatoes, significantly reducing the water loss and firmness decline and maintaining the appearance, total solid, total acid, and ascorbic acid content. This work provided a strategy to fabricate hydrophobic packaging for the preservation of fruits and vegetables.

pH Effect on the Structure, Rheology, and Electrospinning of Maize Zein

As a simple and convenient technology to fabricate micron-to-nanoscale fibers with controllable structure, electrostatic spinning has produced fiber films with many natural advantages, including a large specific surface area and high porosity. Maize zein, as a major storage protein in corn, showed high hydrophobicity and has been successfully applied as a promising carrier for encapsulation and controlled release in the pharmaceutical and food areas. Proteins exhibit different physical and chemical properties at different pH values, and it is worth investigating whether this change in physical and chemical properties affects the properties of electrospun fiber films. We studied the pH effects on zein solution rheology, fiber morphology, and film properties. Rotational rheometers were used to test the rheology of the solutions and establish a correlation between solution concentration and fiber morphology. The critical concentrations calculated by the cross-equation fitting model were 17.6%, 20.1%, 20.1%, 17.1%, and 19.5% (w/v) for pH 4, 5, 6, 7, and 8, respectively. The secondary structure of zein changed with the variation in solution pH. Furthermore, we analyzed the physical properties of the zein films. The contact angles of the fiber membranes prepared with different pH spinning solutions were all above 100, while zein films formed by solvent evaporation showed hydrophilic properties. The results indicated that the rheological properties of zein solutions and the surface properties of the film were affected by the pH value. This study showed that zein solutions can be stabilized to form electrospun fibers at a variety of pH levels and offered new opportunities to further enhance the encapsulation activity of zein films for bioactive materials.

Recent advances in self-assembly behaviors of prolamins and their applications as functional delivery vehicles

Prolamins are a group of storage proteins (zeins, kafirins, hordeins, secalins, gliadins, glutenins, and avenins) found in the endosperm of cereal grains and characterized by high glutamine and proline content. With the high proportion of nonpolar amino acids (40-80%) and peculiar solubility (alcohol (60-90%), acetic acid, and alkaline solutions), prolamins exhibit tunable self-assembly behaviors. In recent years, research practices of utilizing prolamins as green building materials of functional delivery vehicles to improve the health benefits of bioactive compounds have surged due to their attractive advantages (e.g. sustainability, biocompatibility, fabrication potential, and cost-competitiveness). This article covers the recent advances in self-assembly behaviors leading to the fabrication of nanoparticles, fibers, and films in the bulk water phase, at the air-liquid interface, and under the electrostatic field. Different fabrication methods, including antisolvent precipitation, evaporation induced self-assembly, thermal treatment, pH-modulation, electrospinning, and solvent casting for assembling nanoarchitectures as functional delivery vehicles are highlighted. Emerging industrial applications by mapping patents, including encapsulation and delivery of bioactive compounds and probiotics, active packaging, Pickering emulsions, and as functional additives to develop safer, healthier, and sustainable food products are discussed. A future perspective concerning the fabrication of prolamins as advanced materials to promote their commercial food applications is proposed.

Effect of ultrasonic treatment on the stability and release of selenium-containing peptide TSeMMM-encapsulated nanoparticles in vitro and in vivo

Rice selenium-containing peptide TSeMMM (T) with immunomodulatory functions was isolated from selenium-enriched rice protein hydrolysates. However, its biological activity is difficult to be protected in complex digestive environments. In this study, T was encapsulated within zein and gum arabian (GA) through ultrasound treatment to improve its bioactivity and bioavailability. The zein@T/GA nanoparticles were formed using ultrasonic treatment at 360 W for 5 min with a 59.9% T-encapsulation efficiency. In vitro digestion showed that the cumulative release rate of zein@T/GA nanoparticles reached a maximum of 80.69% after 6 h. In addition, short-term animal studies revealed that the nanoparticles had an effect on the levels of tissue glutathione and improved peptides' oral bioavailability. Conclusively, these findings suggest that the ultrasonicated polysaccharide/protein system is suitable for encapsulating active small molecular peptides. Furthermore, it provides a novel foundation for studying the bioavailability of active substances in functional foods.

A Proteomic Approach to Identify Zein Proteins upon Eco-Friendly Ultrasound-Based Extraction

Zein is a type of prolamin storage protein that has a variety of biomedical and industrial applications. Due to the considerable genetic variability and polyploidity of the starting material, as well as the extraction methods used, the characterization of the protein composition of zein requires a combination of different analytical processes. Therefore, we combined modern analytical methods such as mass spectrometry (MS), Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), atomic force microscopy (AFM), or Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) for a better characterization of the extracted zein. In this study, we present an enhanced eco-friendly extraction method, including grinding and sieving corn seeds, for prolamins proteins using an ultrasonic extraction methodology. The use of an ultrasonic homogenizer, 65% ethanol extraction buffer, and 710 µm maize granulation yielded the highest protein extraction from all experimental conditions we employed. An SDS PAGE analysis of the extracted zein protein mainly revealed two intense bands of approximatively 20 and 23 kDa, suggesting that the extracted zein was mostly α-zein monomer. Additionally, MS analysis revealed as a main component the α-zein PMS2 (Uniprot accession no. P24450) type protein in the maize flour extract. Moreover, AFM studies show that extracting zein with a 65% ethanol and a 710 µm granulation yields a homogeneous content that could allow these proteins to be employed in future medical applications. This research leads to a better understanding of zeins content critical for developing new applications of zein in food and pharmaceutical industries, such as biocompatible medical vehicles based on polyplexes complex nanoparticles of zein with antimicrobial or drug delivery properties.