Zein Films Research Articles

Zein film loaded with Fructus Ligustri Lucidi essential oil: Preparation, characterization and application in fresh-cut apple preservation

Fresh-cut fruits and vegetables are a type of convenient, ready-to-use food that offers consumers a healthy choice. However, the peeling and slicing operations make them susceptible to microbial contaminations and oxidation. In this study, zein was used as the film-forming substrate, and Fructus Ligustri Lucidi essential oil (FEO), a natural bacteriostatic agent, was incorporated into zein film to prepare a film with antibacterial and antioxidant properties to prolong the shelf life of fresh-cut fruits and vegetables. Polyethylene glycol 400 (PEG400) and glucose were used as plasticizers, and the optimal formulation of the film (FZF) was obtained by orthogonal experiment: 10% PEG400, 5% glucose and 10% FEO. The films were characterized by scanning electron microscope (SEM), Fourier transform infrared spectrum (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA), and the influence of FEO on the physical, chemical, and biological characteristics of the films was explored. The results demonstrated that FEO was successfully loaded into zein film and distributed evenly. The FZF film exhibited excellent antioxidant activity, when the concentration of FEO was 200 μg/mL, the scavenging rate of DPPH and ABTS was 81.63 ± 0.69% and 91.44 ± 0.55% respectively. Furthermore, the FZF film showed antibacterial properties against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) and low cytotoxicity in vitro. Moreover, the FZF film demonstrated anti-browning capabilities, effectively prolonging the shelf life of fresh-cut apple slices. Thus, the FZF film possesses considerable potential for utilization in food packaging.

Characterization of zein-based films plasticized with deep eutectic solvents and their use in the preservation of harvested mango fruit

The harsh environmental impact of synthetic plastics used in packaging is driving the search for biobased alternatives. To address this urgent need, we explored the syntheses of zein films containing deep eutectic solvents (DESs). Four DESs (hydrogen bond acceptor: choline chloride (ChCl); hydrogen bond donors: citric acid (Ca), lactic acid (La), urea (Ur) and ethylene glycol (Eg)) were incorporated into zein as plasticizers, and their structural, physical, mechanical and antibacterial properties were evaluated. The results showed that the zein films plasticized with the DESs exhibited enhanced mechanical and barrier properties and hydrophilic surfaces with limited water swelling. Zein films prepared by adding DESs showed varying antibacterial effects against both Escherichia coli and Staphylococcus aureus. Among these films, the zein films plasticized with ChCl-Ca had the best mechanical, water barrier and antibacterial properties. The observation of scanning electron microscopy displayed that zein film containing ChCl-Ca had a denser microstructure compared to other plasticized films. Furthermore, we used pure zein and ChCl-Ca plasticized zein to coat mango fruit and investigated their preservation effects. The results showed that both coating treatments reduced the weight loss and delayed the declines in the peel chromaticity L*, pulp firmness and soluble solids content in mango fruit during storage comparing to control and ethanol treatment, but coating with ChCl-Ca plasticized zein had a more prominent effect in preserving mango fruit. We suggest that plasticization of zein films with ChCl-Ca is a valuable and convenient use of protein materials in mango preservation.

Enhanced effect of ultrasound and gelatin on physical and antibacterial properties of thymol/hollow mesoporous silicon spheres doped zein film

A new antibacterial film, Thy-HMSS/zein film, was prepared from hollow mesoporous silicon spheres loaded with thymol (Thy-HMSS) by ultrasonic optimization casting method (150 W power ultrasonic treatment solution for 3 min). To further enhance the film quality, a composite film, Thy-HMSS/Zein-gelatin film (Thy-HMSS/ZG film), was created by incorporating gelatin into zein. Compared to film containing the same amount of Thy, the effective protection and slow-release effect of HMSS on Thy resulted in a lower release rate of Thy in Thy-HMSS/zein films in the first 2 h, while the total amount of Thy released increased by 10 %. The appearance and structure of the films were optimized by ultrasonic treatment, which reduced the surface bubbles, cross section pores and particle agglomeration. The addition of gelatin enhanced the antibacterial effect of the film, the inhibition zone diameters of Escherichia coli and Staphylococcus aureus can be increased by up to 123.53 % and 159.37 %, respectively. Both Thy-HMSS/zein film and Thy-HMSS/ZG film showed no toxicity in cytotoxicity tests and exhibited good anti-corrosion ability when applied to blueberry preservation. Therefore, the combination of HMSS encapsulation with ultrasonic treatment and gelatin addition represents a suitable and straightforward approach for producing excellent antimicrobial films with superior appearance, structure, and antibacterial properties. This method holds significant potential in the food industry for producing sustainable active packaging materials while also offering new avenues for employing various techniques in films preparation.

Performance enhancing of saturated fatty acids with various carbon chain lengths on the structures and properties of zein films in alkaline solvents

Zein, a storage protein rich in hydrophobic amino acids found in maize endosperm, offers significant potential for applications in food packaging. Previous studies on zein films primarily focused on the dissolution of zein in organic solvents. In this study, zein was dissolved in an alkaline solution instead of organic solvents. The effects of fatty acids with varying carbon chain lengths, namely decanoic acid, lauric acid, and palmitic acid, on the structure and properties of zein films were investigated. Alkali-solubilized zein exhibited a various degree of deamidation related to fatty acids after film formation in which decanoic acid significantly reduced the deamidation of zein, while palmitic acid had the opposite effect. Various characterizations confirmed that fatty acids were evenly distributed within the film matrix, disrupting the intermolecular interactions of zein and preventing zein molecules from aggregation; this eventually led to a tightly structured film. The addition of fatty acids, specifically decanoic acid and lauric acid, significantly enhanced the performance of the zein films. After loading decanoic acid or lauric acid, the almost opaque zein films had a visible light transmittance of over 50% while maintaining an excellent UV light blocking property. The tensile strength and elongation at break of the films were improved, and their water vapor permeability was reduced by an order of magnitude. This study provides insights into zein plasticization and paves the way for developing organic solvent-free food packaging.

Deep eutectic solvent as plasticizing agent for the zein based films

This study explores, the impacts of incorporating of deep eutectic solvent (DES) as plasticizer on the characteristics of zein films. Investigation focused on examining the mechanical, thermal, surface, and microstructural properties of zein films that were plasticized using DES. The findings of the study revealed that by adding DES to zein films, there was an observed improvement in transparency. Additionally, it was observed that up to a 20% addition of DES led to a reduction in water vapor permeability (WVP). However, beyond this level, the WVP increased as the surface hydrophobicity decreased. The films that were plasticized with DES showed higher tensile and burst strength values than control. However, there was a decrease in the elongation at break and burst distance, except for the film containing 30% DES. The addition of DES as plasticizer resulted in smoother surface morphology compared to the control, and all films revealed homogeneous and non-porous surface and cross-section microstructure. The films plasticized with DES displayed three different thermal degradation temperatures resulting in higher thermal stability. The FT-IR spectrum of films showed similar backbone structure including Amide I, II and III bands. However, 5% DES plasticized film showed different secondary structural peaks of Amide I band due to lower α-helix and higher β-sheet and random coil content. The findings of this investigation indicate that the employment of DES as plasticizer in biodegradable polymer films can yield enhanced mechanical and barrier characteristics compared to conventional plasticizers, thus demonstrating its potential for effective use.

Electron irradiation of zein protein-loaded nano CaO2/CD for enhancing infectious diabetic wounds with adaptive hydrophobicity-to-hydrophilicity

Chronic diabetic cutaneous wounds resulting from inflammatory conditions present an ongoing challenge for current therapies and impose a significant burden on individuals with diabetes, impacting their quality of life. Infection-related diabetic skin wounds require dry conditions to inhibit bacterial growth. However, as the wounds progress, moisture becomes necessary to facilitate the healing process. In this study, we propose a novel therapeutic strategy for diabetic skin repair by creating bio-dressings with adjustable “hydrophobic” and “hydrophilic” characteristics to accommodate the changing stages of the disease. We developed a skin dressing by loading calcium peroxide (CaO2) nanoparticles onto carbon dots (CD)-modified irradiated zein (Ir-Zein). This dressing releases reactive oxygen species (ROS) from CaO2, providing antibacterial effects, while the presence of CD enables a sustained release of CaO2. The calcium ions produced by CaO2 degradation further promote skin regeneration. Ir-Zein protein, a cost-effective and easily processed natural plant protein, exhibits excellent biocompatibility. Importantly, in diabetic rats with full-thickness skin defects, the CaO2/CD@Ir-Zein film significantly accelerated the healing of chronic wounds. Mechanistic investigations revealed that the film effectively reduced inflammation by inhibiting the polarization of macrophages towards the M1 phenotype and capturing pro-inflammatory cytokines. In summary, our findings demonstrate the effectiveness of the CaO2/CD@Ir-Zein film’s “adaptive hydrophobicity-to-hydrophilicity” in promoting the transition of chronic wounds from the inflammatory stage and skin repair. CaO2/CD@Ir Zein is a novel bio-dressing that can adapt to the changing environment of infected diabetic skin wound healing.

Edible electrospun zein nanofibrous scaffolds close the gaps in biofilm formation ability between microorganisms

Biofilm is an important survival mode of microorganisms in nature. Biofilm culture is supposed to be a way of learning from nature to endow microorganisms with a strong tolerance. However, microorganisms possess different biofilm formation abilities, and universal scaffolds, especially edible scaffolds, suitable for fast biofilm formation are not found yet. Zein is a hydrophobic and biocompatible prolamine-rich protein from corn and is one of the most used biomacromolecules now. In this work, natural zein was utilized to produce electrospun zein nanofibrous biomaterial. The results demonstrate that edible electrospun zein nanofibrous scaffolds significantly enhance biofilm formation, where bacterial probiotics and yeasts are 0.9–1.4 Log cfu/cm2 (8–25 × ) and 1.7–3.3 Log cfu/cm2 (50–2000 × ) higher than the values on polystyrene plates and zein films, respectively. Gaps in biofilm formation abilities between bacteria and yeasts are narrowed from 1.7–1.8 Log cfu/cm2 (50–63 × ) to 0.5–0.6 Log cfu/cm2 (3–4 × ), respectively. Biofilms quickly formed on electrospun zein nanofibrous scaffolds before the occurrence of serious swelling deformation of the scaffolds. This is the first attempt to use edible electrospun fibrous scaffolds based on natural biomacromolecules for enhancing biofilm formation, crucially important for the application of probiotics and yeast in food and medical industries. Electrospun zein nanofibrous scaffolds can serve as powerful tools to enhance the biofilm formation of valuable food microorganisms and close the huge gaps in biofilm formation abilities between microorganisms, providing a convenient and universal strategy to produce biofilm-phenotyped probiotics and yeasts.

Engineering biodegradable controlled gelatin-zein bilayer film with improved mechanical strength and flexibility

Compiling hydrophobic and hydrophilic proteins to form mechanically reliable bilayer film with improved water barrier properties and hydrophobicity to replace petroleum-based standards is challenging because fabricating compatible surfaces and flexible film with interlinked interfaces is complex. The mechanical properties of gelatin and zein layers exhibited unique variations, and synergistic enhancement of bilayer properties reflected robust layer-by-layer (LBL) interactions. To overcome the problem of impaired integrated surface, viscously cross-linked zein film forming solution (FFS) by glyoxal (GX) introduced compact and closely entangled network formation with cross-linking of gelatin film. Zein surface compatibility and flexibility by GX and polyethylene glycol (PEG 400) synergized with the gelatin layer closed to compare flexible plastic materials such as PE and PP besides modulated color and transparency. Enhancing flexible formation was mechanized by acetic acid as solvent of zein solution after long-range repulsion during casting on well-manageable plasticized and cross-linked gelatin film with glutaraldehyde (GA) and PEG 400, respectively. Elongation (E%) was achieved by nearly 192% with modified tensile strength (TS) and Young's modulus (YM). Cross-linkers, especially GX, resulted in lower water solubility (WS), and joint layers resulted in controlled water vapor permeability (WVP) of bilayer films. Decreased surface roughness and WS increased water contact angle (WCA). FTIR spectroscopy, XRD analysis, DMTA, and SDS-PAGE analyzed cross-linking mode and intensity. Hence, gelatin-zein bilayer films showed significant potential for improving value-added functional properties.

Comparison of green and synthetic silver nanoparticles in zein-based edible films: Shelf-life study of cold-stored turkey breasts.

This study aimed to compare the effect of zein edible film containing silver nanoparticles produced by green tea leaf extract (Z-gAgNPs) with zein film containing synthetic silver nanoparticles (Z-AgNPs) on the shelf life of turkey breast during refrigerated storage. The produced silver nanoparticles were analyzed using dynamic light scattering (DLS), UV-Vis spectroscopy, X-ray diffraction (XRD), scanning electron microscope (SEM), and atomic force microscope (AFM). According to the obtained results, the green fabricated silver nanoparticles (gAgNPs) showed higher polydispersity index (PDI), stability, homogeneity, spherical shape without cavity, and lower size compared to the synthetic silver nanoparticles (AgNPs). The studied treatments were divided into four groups, including 1- control (C) (turkey breast meat without packaging), 2- Z (turkey breast meat packaged with zein film), 3- Z-AgNPs (turkey breast meat packaged with zein film containing 0.5% (w/w) of AgNPs), and 4-Z-gAgNPs (turkey breast meat packaged with zein film containing 0.5% (w/w) of gAgNPs). The treatments were analyzed for 12 days with 3-day intervals in refrigerator conditions. In general, the measurement of total viable count, total volatile basic nitrogen (TVB-N), and pH values showed that Z-gAgNPs film significantly (p ≤ .05) delayed the spoilage of the studied samples until the end of the 12th day of storage and Z-AgNPs, Z, and C treatments were in the next ranks, respectively. It is concluded that the biofabricated silver nanoparticles using green tea leaf extract have more appropriate physicochemical features and higher efficiency compared to the synthesized silver nanoparticles using chemical methods in zein edible films in improving the shelf life of the cold-stored turkey breast meat and can be introduced as a promising alternative to the plastic packaging.

Fabrication of depolymerized zein films via high-intensity ultrasound for ethylene adsorption packaging

The aim of the study was to prepare depolymerized zein (D-zein) films for fruit packaging. High-intensity ultrasound (HIU) treatment was employed to stretch the chemical structure of zein protein, and improve the ethylene adsorption efficiency of D-zein films. The study of circular dichroism spectra, fluorescence spectra, particle size, zeta-potential, and total sulfhydryl group content revealed that the depolymerized zein had stretched structure via a moderate HIU treatment (400 W, 15 min). The structural, mechanical, barrier properties, ethylene adsorption efficiency, and application were used to analyze the performance of the D-zein films. In all treatment groups, bananas coated with the D-zein-15 film exhibited favorable browning rate, weight loss rate, flesh hardness, and sensory properties during storage at 25 °C for 10 d. The results indicated that depolymerized zein films could improve the ethylene adsorption efficiency and effectively prolong the shelf life of bananas.

Incorporation of cinnamaldehyde, carvacrol, and eugenol into zein films for active food packaging: enhanced mechanical properties, antimicrobial activity, and controlled release.

Active packaging with antimicrobial functions to improve the quality and extend the shelf life of food products has gained great interest. Because commercial plastic packaging materials are not biodegradable and cause great environmental problems, plant-derived natural materials have been widely studied for the application of biodegradable packaging materials. Herein, we reported a study of essential oils (EOs)-loaded zein film. Cinnamaldehyde (CIN), carvacrol, and eugenol were added to equip the films with antimicrobial effects, while polyethylene glycol (PEG) and oleic acid (OA) were selected for the improvements of mechanical properties. The results showed that PEG efficiently improves the tensile strength and elongation (%E) of zein films compared to OA, although PEG induced weaker water barrier properties of the films than OA. FTIR spectra confirmed the formation of the hydrogen bonds between zein and PEG/OA. The EO-embedded zein film showed better antimicrobial effects than EO themselves. CIN-embedded films showed the highest antimicrobial effect among the three EOs. The sizes of the inhibition zones against Staphylococcus aureus of PEG-added zein films with 1%, 3%, and 5% CIN were 5.67, 12.67, and 16.67mm, which were larger than that of pure CIN, with the sizes of 0.00, 3.00, and 4.67mm, respectively. The developed films demonstrate a gradual release of EOs and show antimicrobial effects up to 96 h, indicating their high potential for the applications as active food packaging.

Characterization of Nano-SiO2/Zein Film Prepared Using Ultrasonic Treatment and the Ability of the Prepared Film to Resist Different Storage Environments.

This study has developed, ultrasound-assisted, a novel food packaging film (U-zein/SiO2) for food packaging applications. Incorporating an optimal concentration of 18 mg/mL of nano-SiO2 and subjecting the film to 10 min of ultrasonic treatment resulted in a remarkable increase of 32.89% in elongation at break and 55.86% in tensile strength. In addition, the incorporation of nano-SiO2 effectively reduces the water content and solubility of the composite film, resulting in improved water/oxygen barrier properties. These physiochemical properties were further improved with the application of ultrasound. The analysis of attenuated total reflectance-Fourier transform infrared, X-ray diffraction, differential scanning calorimetry, and scanning electronic microscope demonstrated that the ultrasound treatment improved the hydrogen bonds, improved thermal stability, molecular arrangement, structure stability, and intermolecular compatibility of the composite film, resulting in enhanced physio-mechanical properties of the film. In addition, the ultrasound treatment led to a smoother film surface and reduced the pores on the film's cross-section. Moreover, the U-zein/SiO2 film exhibited excellent mechanical and water/oxygen barrier properties in different storage environments over a period of 30 days. These results offer sound theoretical support for the practical application of the prepared preservative film.

An innovative solid-phase biosensor for rapid on-site detection of N-nitrosodimethylamine incorporating zein film and upconversion nanoparticles

Pickled frequently contains nitrosodimethylamine (NDMA), a mutagenic and carcinogenic substance that is dangerous for the general public's health. This study reports on the fabrication of a fluorescent biosensor using zein film and aptamer functionalized upconversion nanoparticles (UCNPs) for on-site monitoring of NDMA in meat. UCNPs were first prepared followed by aptamer binding and mixing with zein film, which was further conjugated with cDNA of dabcyl modified at 5′. The fluorescence resonance energy transfer (FRET) mechanism between the UCNPs and dabcyl was exploited. The fluorescence signals of the zein film recovered when NDMA was present because it was selectively collected by the particular aptamer and damaged the cDNA structure. The designed functionalized zein film was used for on-site and portable determination of NDMA with a lower limit of detection of 0.017 ng/mL, and possessed a satisfactory recovery ranging from 95.8% to 100.2% with no significant difference compared with the GC–MS method.

Self-assembly of zein in aqueous acetic acid and ethanol solvents: Effect on mechanical properties of the zein film

The solubility of zein varies with solvent types, therefore, affecting the physicochemical properties of film-forming solutions (FFS) and the fabricated zein films. The transformation of α-helix to β-sheet in zein molecules varied with solvent polarity, which influenced the self-assembly of zein. In this research, zein film was fabricated using various concentrations of aqueous acetic acid solvent (AAS) and aqueous ethanol solvent (AES). Zein was soluble over 96 % in 40–80 %(v/v) AAS and 60–80 % in 75–95 %(v/v) AES, respectively. SDS-PAGE reveals that the insolubility of the β-zein and dimers of α-zein was responsible for the solubility difference. The formation of the zein network affects the mechanical and physical properties of the film. The tensile strength of the film was over 25 MPa when the β-zein was soluble, and the zeta potential of FFS was over + 25 mV. Films fabricated with AAS had at least five times higher Young’s modulus than AES films. The transformation ratio of α-helix to β-sheet and reassembling of β-sheet into strips during self-assembly depended on the water percentage in the FFS. The free water stuck in the film network contributed to the moisture content of 8–10 % in AAS films and 11–16 % in AES films in films was observed by LF NMR. This study suggested that a stable FFS (zeta potential > +40 mV) and organized network in the film could be obtained by dissolving zein in AAS (≤ 70 %, v/v) than in AES.

Natural and biocompatible dressing unit based on tea carbon dots modified core-shell electrospun fiber for diabetic wound disinfection and healing

Wound infection and healing in patients with diabetes is one of the complex problems in trauma treatment. Therefore, designing and preparing an advanced dressing membrane for treating the wounds of such patients is essential. In this study, a zein film with biological tea carbon dots (TCDs) and calcium peroxide (CaO2) as the main components for promoting diabetic wound healing was prepared by an electrospinning technique, which combines the advantages of natural degradability and biosafety. CaO2 is a biocompatible material with a microsphere structure that reacts with water to release hydrogen peroxide and calcium ions. TCDs with a small diameter were doped in the membrane to mitigate its properties while improving the antibacterial and healing effects of the membrane. TCDs/CaO2 was mixed with ethyl cellulose-modified zein (ZE) to prepare the dressing membrane. The antibacterial properties, biocompatibility and wound-healing properties of the composite membrane were investigated by antibacterial experiment, cell experiment and a full-thickness skin defect. TCDs/CaO2 @ZE exhibited significant anti-inflammatory and wound healing-promoting properties in diabetic rats, without any cytotoxicity. This study is meaningful in developing a natural and biocompatible dressing membrane for diabetic wound healing, which shows a promising application in wound disinfection and recovery in patients with chronic diseases.

Antimicrobial pseudolatex zein films with encapsulated carvacrol for sustainable food packaging

Environmental problems caused by food packaging impede the sustainability of packed food. Therefore, efficient and environmentally–friendly solutions need to be urgently implemented. Zein is water–insoluble plant protein which can form biodegradable films that have potential to be used as sustainable food packaging. In this work, zein films (zFc) were prepared from dispersions of zein nanocapsules (zNC) containing carvacrol, using pseudolatex technology. zNC were characterized for zeta potential and size. Influence of carvacrol on zFc water resistance, optical and mechanical properties was tested. Encapsulation efficiency and release curves of carvacrol were determined. Antimicrobial activity of zFc with 20% carvacrol was tested under dynamic conditions. It was shown that continuous zein films can be prepared by coalescence of zNC, using pseudolatex technology. Results showed that tested carvacrol concentrations do not affect zNC and zFc properties. Antimicrobial activity of zFc was found to be sufficient to block the growth of Staphylococcus aureus.

Edible film based on corn zein containing dill extract and essential oil/β-cyclodextrin inclusion complex: Shelf life enhancement of common carp fillet.

The aim of this study was to examine the impacts of corn zein edible film (Z) fortified with dill leaves extract (DE) and encapsulated dill essential oil with β-cyclodextrin (nDEO) on the quality of refrigerated common carp fillet. Gas chromatography/mass spectrometry (GC/MS) analysis showed that the most frequent substances of DEO were apiol (35.1%) and carvone (31.4%), respectively. Designated treatments were as follows: (1) Control (C), (2) Z, (3) Z-DE, (4) Z-DEO, (5) Z-nDEO, (6) Z-DE-DEO, and (7) Z-DE-nDEO. The physicochemical properties (thickness, moisture percent, tensile strength, elongation at break, Young's modulus, color, morphology, functional groups, and thermal resistance) of the activated films significantly improved (p ≤ .05). The total viable counts, lactic acid bacteria, Enterobacteriaceae, and psychrotrophic bacteria significantly decreased in all wrapped fillets compared to the unwrapped ones (p ≤ .05). Throughout storage period, the wrapped fillets exhibited lower changes in pH, thiobarbituric acid reactive substances, and total volatile-based nitrogen values than the unwrapped fillets. According to the sensory findings, incorporating DE and nDEO in the zein films created significantly desirable aroma and flavor in the wrapped samples during storage time (p ≤ .05). Encapsulation of DEO with β-cyclodextrin significantly fortified preservative effects of the films in fish fillets during storage period (p ≤ .05). In conclusion, the designated composite zein edible film containing DE and nDEO can be introduced as an active edible packaging in the shelf life improvement of common carp fillets during cold storage.

Bioplastic film making properties of quality protein maize (QPM) zein

AbstractBackground and ObjectiveQuality protein maize (QPM) has abundant γ‐zein, which crosslinks itself and other zeins through disulfide bonding. The work aims to develop zein bioplastics with better functionality by using QPM zein. Physical properties of cast QPM zein films from QPM maize were compared with zein films from regular maize types and commercial zein, all without added plasticizers.FindingsQPM zein contained 3.8% cysteine compared with 1.8%–2.7% in regular maize zeins and 1% in commercial zein and the QPM zein had a much higher proportion of γ‐zein. QPM zein films cast from glacial acetic acid (GAA) were opaque but absorbed the least liquid (≈16%) and swelled less (≈11%) after buffer immersion than the other zein films and aqueous ethanol‐cast films. Notably, the GAA‐cast QPM zein films became highly flexible after ambient storage, whereas the other zein films remained brittle.ConclusionsThe low buffer uptake and swelling of QPM zein films is attributed to crosslinking involving the cysteine‐rich γ‐zein polypeptides. Their flexibility is attributed to better solubilization of the zein in GAA and water molecules bound to the γ‐zein polypeptides acting as a plasticizer.Significance and NoveltyQPM zein can enable the formation of flexible zein bioplastics without added plasticizers.

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.

Do kafirin bioplastic materials have unique functional characteristics?

AbstractBackground and ObjectivesThere is considerable interest in kafirin, sorghum prolamin, as a bioplastic material because it apparently produces bioplastics with superior functional properties. This review evaluates the evidence, focussing on research directly comparing the properties of kafirin bioplastics (films and elastomers) with those from zein and gluten.FindingsKafirin and zein are more hydrophobic than gluten but there is little difference in hydrophobicity between them. Kafirin and zein films have better moisture barrier properties than gluten films. Films made from total kafirin (α‐, β‐, and γ‐kafirins) are stronger and take up less moisture than films from commercial zein (essentially α‐zein). However, total kafirin‐ and total zein films have similar moisture uptake. Also, there is little difference in oxygen barrier properties between total kafirin‐ and commercial zein films. Total kafirin elastomers have better elastic recovery than commercial‐ and total zein elastomers and similar elastic recovery to gluten.ConclusionsThe better functional properties of kafirin bioplastics compared to commercial zein bioplastics seems to be largely due to the greater disulfide bonded polymerization of kafirin polypeptides, involving the cysteine‐rich β‐ and γ‐kafirin classes.Significance and NoveltyThis work should stimulate research into disulfide‐bonded polymerization of prolamins to improve their bioplastic functionality.