Wheat gluten films cross-linked with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide

Wheat gluten films were cast from aqueous dispersions containing 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) as cross-linking reagents and glycerol as a plasticizer. Cross-linking was carried out to improve film properties such as water sensitivity and tensile strength. Films were characterized by measuring protein and water content, amount of amino groups, swelling of the films in water, and mechanical properties such as tensile strength (σ_max) and strain at maximum stress ( at σ_max). The use of different ratios of EDC to COOH resulted in different tensile properties and different percentage of swelling, which was attributed to the degree of cross-linking in the film. At a ratio of EDC/NHS/COOH=0.5/0.5/1, films had a water content of 10–11.5% and showed the highest σ_max (2.8±0.9 MPa), the lowest at σ_max (142±67%), and the lowest swelling (46%) compared to σ_max=1.7±0.4 MPa, at σ_max=257±63%, and swelling=68% for native gluten films.     

Production of composites by using gliadin as a bonding material

In previous papers, a new technology that produces biopolymer composites by particle-bonding was introduced. During the manufacturing process, micrometer-scale raw material was coated with a corn (Zea mays L.) protein, zein, which was then processed to form a rigid material. The coating of raw-material particles with zein makes use of the unique property of this protein in aqueous ethanol solution. In this paper, it is shown that the behavior of a wheat (Triticum aestivum L.) protein, gliadin, is very similar to zein in aqueous ethanol. Size variation of aggregates in 45-65% aqueous ethanol was investigated with a turbidimeter in conjunction with Size Exclusion Chromatography. Confirming the resemblance of gliadin to zein in terms of aggregation behavior in aqueous alcohol, composites were fabricated by particle-bonding and their mechanical property was measured with a Universal Testing Machine. Test results showed that gliadin is a good substitute for zein in the production of composites.     

Oxidation of commercial (α-type) zein with hydrogen peroxide improves its hydration and dramatically increases dough extensibility even below its glass transition temperature

To improve the rheological properties of zein doughs, α-type zein and zein-starch doughs were prepared with the oxidising agents, hydrogen peroxide and peroxidase, which strengthen gluten-based doughs by cross-linking. Hydrogen peroxide and peroxidase increased zein dough extensibility compared to preparation with water. Hydrogen peroxide prepared zein doughs were extensible and cohesive below zein’s glass transition temperature. The doughs did not exude water and maintained flexibility when stored. Confocal laser scanning microscopy revealed that in zein-starch doughs prepared with hydrogen peroxide a thin continuous zein matrix was formed around the starch granules, whereas doughs prepared with water exhibited clumps of granules. SDS-PAGE of zein doughs and films treated with the oxidising agents showed no evidence of zein polymerisation, nor did Fourier transform infrared spectrometry reveal any significant changes in secondary structure. Further, hydrogen peroxide treatment did not increase zein film glass transition temperature, but it did increase transition enthalpy, and film water uptake increased with hydrogen peroxide concentration. The greatly increased extensibility of hydrogen peroxide prepared zein doughs and their improved water-holding are not due to oxidative cross-linking. It is proposed that the effects are primarily due to hydroxylation of amino acid aliphatic side chains, improving hydration through hydrogen bonding.     

Pasting Profiles and Solubility of Native and Cross-Linked Corn Starch inDimethylsulfoxide-Water Mixtures

The pasting profiles of native and cross-linked corn starch in dimethylsulfoxide (DMSO)–water mixtures were investigated with a Rapid Visco Analyser. The temperature profile included an isothermal step of 1 min at 30 °C, followed by a linear gradient to 75 °C in 3 min and finally an isothermal step of 20 min at 75 °C. The profiles were characterised by an initial peak (at 75 °C) followed by a trough, much as is the case with profiles of such starch in water. Increasing the DMSO concentration in the DMSO–water mixture from 70–97·5% (by weight), without changing the starch concentration, resulted in lower end-viscosities. The RVA pasting profiles of a series of sodium trimetaphosphate (STMP) and epichlorohydrin (ECH) cross-linked corn starches were investigated in 92·5% DMSO at different dry matter (d.m.) contents. At high starch concentrations (>60% d.m.), the end viscosity increased with the degree of cross-linking. At lower starch concentrations (<6% d.m.), the more highly cross-linked starches yielded lower peak- and end-viscosities than starches with lower degrees of cross-linking. The solubilisation of the starches in 92·5% DMSO was complete for the native starch and decreased considerably for the highly cross-linked starches. Light microscopy showed that the cross-linked starches, upon heating in DMSO–water, were converted to a biphasic system consisting of insoluble granule remnants and a starch solution.     

Zein: the industrial protein from corn

Zein is the major storage protein of corn and comprises ≈45–50% of the protein in corn. It was first identified in 1897, based on its solubility in aqueous alcohol solutions. Zein isolate is not used directly for human consumption due to its negative nitrogen balance and poor solubility in water. Current zein manufacture is limited to ≈500 tonnes per year from corn gluten meal. Zein sells for ≈US$10–40 per kilogram, depending on purity. The ability of zein and its resins to form tough, glossy, hydrophobic grease-proof coatings and their resistance to microbial attack have been of commercial interest. Potential applications of zein include use in fiber, adhesive, coating, ceramic, ink, cosmetic, textile, chewing gum and biodegradable plastics. These new applications of zein appear promising, but requires the development of low-cost manufacturing methods. This paper reviews the present status of the chemistry, properties, uses and methods of manufacturing zein. The characteristics of zein are discussed in terms of its composition, structure, solubility in various solvents and gelation properties.     

羧甲基壳聚糖(NCMC)对玉米种子蛋白质合成与积累的影响

用羧甲基壳聚糖处理抽穗期玉米穗轴和花丝,与未处理对照相比,玉米种子贮藏蛋白的含量提高10.8%,其中醇溶蛋白含量提高33.8%,这一结果表明,天然来源的羧甲基壳聚糖,可以作为一种新型蛋白质生物调节剂,用以提高作物蛋白质产量和改进蛋白质量。     

Nano-structure and properties of maize zein studied by atomic force microscopy

Atomic force microscopy was used to investigate the nanostructure of zein from maize (Zea mays). In aqueous ethanol solution zein exists as small globules with diameters between 150 and 550 nm. The mechanism of zein film formation was also explored. The characteristic film structure consists of a meshwork composed of doughnut structures formed from asymmetric rods joined to each other.     

Effect of pH and ethanol content of solvent on rheology of zein solutions

Zein, a corn protein, is a mixture of the polypeptides α-, γ-, β-, and δ-zein. α-Zein and γ-zein comprise 70–85% and 10–20% of total zein mass, respectively. Both peptides have similar amino acid composition, except γ-zein is rich in cysteine. The presence of cysteine has been associated with gelation of zein solutions. A common solvent for zein is aqueous ethanol. Preliminary results suggested that pH and ethanol content affect the rheology of zein solutions. Our objective was to investigate the effect of ethanol content (65–90%) and pH of the solvent (2, 6, and 12) on rheological properties of zein solutions (20% w/w) containing γ-zein. Steady shear tests and oscillatory time sweeps were performed to determine flow behavior and gelation time of zein solutions. Results indicated that α-zein solutions were nearly Newtonian while those containing γ-zein showed shear thinning behavior. At high pH, γ-zein increased the consistency index (K) and shortened gelation time. Results were attributed to the cysteine in γ-zein. High pH promoted formation of disulfide bonds leading to higher K values and shorter gelation times. Results of this work are expected to be useful in the design of zein extraction processes and the development of new zein applications.     

Serial batch extraction of zein from milled maize

Prolamine-rich, water insoluble proteins (zeins) can be extracted from milled maize by vigorous mixing in heated ethanol solutions. Whenever solvent extraction is used process cost considerations require that all the solvent be recovered. Because of the low zein content of maize rinsing extract liquid from the extracted maize particles must be done in a way that minimizes dilution. The solid mass fraction of milled grain slurry that can be pumped is 0.25 or less. Because the mass fraction of zein in maize is only approximately 0.05, the zein mass fraction of a batch extract will be less than 0.015. To increase the zein concentration, a batch extract (liquid and fines) can be repeatedly separated from the extracted solid particles and used to extract fresh milled grain. A series of batch extractions with extract reuse can approach the performance of a continuous counter-current solids/liquid extraction, which would be preferable at a commercial scale. Extract reuse is constrained by losses of liquid with the extracted grain and by reductions of the extracting capacity of the extract due to the increasing solute or fines content. By examining the extract composition and yield of a series of batches, it is possible to estimate the zein concentration that could be achieved in a continuous, countercurrent process and to examine effects of higher zein concentrations on extraction that would be inaccessible with a single batch. The centrifugate concentrations for a series of maize extractions in which the extracted maize and extract solution were cooled prior to centrifugation were analyzed. The data were fit with a model based on a maximum zein concentration in the extract. The fit indicates that the protein content of the liquid centrifugate will not exceed 2% for any series of similar batch extractions, by using centrifugation to separate the maize from the extraction slurry after cooling it to ambient temperature. This contrasts with concentrations of zein of 10% or more achieved by extracting corn gluten using similar conditions. Although the concentration of zein in gluten is higher we believe the concentration difference is mainly due to chemical changes to the zein that take place in the gluten production and the methods used to extract zein from gluten.     

Blend films based on silk fibroin/hyaluronic acid

Protein and polysaccharide was the most important extracellular matrix in dermal tissue. In this study, Silk fibroin (SF) / hyaluronic acid (HA) blend films mimicking the dermal tissue components were prepared and investigated. The results indicated that HA and SF has a good miscibility, HA interfered with SF to form crystal structure. By using EDC as cross-linker, effective cross-linking function on SF and HA macromolecules was reacted, the water solubility of the blend films decreased obviously after being cross-linked by EDC. The existence of EDC could promote SF to form Silk I structure. L929 cells were seeded on these blend films and showed normal attachment morphology. Cell-matrix interactions established by newly formed extracellular matrix were observed after 5 days in culture. The MTT assay showed that cell proliferation on the SF/HA blend films were enhanced significantly compared with that on the SF and HA films. These new 2D SF/HA blend films provided a favorable microenvironment for the proliferation of L929 cells and hold a potential for dermal tissue regeneration.     

Two fraction extraction of α-zein from DDGS and its characterization

Zein was recovered from corn distiller's dried grains with solubles (DDGS) by a modified method using 70% (w/w) aqueous 2-propanol (70-IPA) or 70% (v/v) aqueous ethanol (70-EtOH) solvents, and a commercial method using 88% (w/w) aqueous 2-propanol (88-IPA). Yield, purity, and film properties of the isolated zein were determined. The modified procedure extracted two fractions of zeins: a mostly α-zein fraction, and a mostly γ-zein fraction. The modified method increased α-zein yield from 4% to 14%. Enzyme cellulase pretreatment did not improve zein yield, but grinding did. The α-zein fraction showed electrophoretic bands at 40, 22, 19, and 10 kDa, corresponding to α-zein dimer, α₁-zein, α₂-zein, and δ-zein, respectively. The α-zein of DDGS retained its film forming capability. The α-zein film of unmodified DDGS was cloudy and rough, unlike the clear and smooth films of α-zeins isolated from corn gluten meal and enzyme-treated DDGS.     

量子点探针应用于粮油中黄曲霉毒素免疫检测的研究

为改良检测技术,拓宽量子点探针在农产品安全领域的应用范围,制备了用于粮油中黄曲霉毒素检测的2种量子点探针,即碳量子点(CQD)探针和石墨烯量子点(GQD)荧光免疫探针,研究2种探针应用于黄曲霉毒素检测中的可行性。采用绿色合成方法,发现以0.375g/m L柠檬酸水溶液中获得的石墨烯量子点荧光强度最强。利用1-(3-二甲氨基丙基)-3-乙基碳二亚胺盐酸盐(EDC·HCL)和N-羟基琥珀酰亚胺(NHS),将碳量子点和GQD与抗黄曲霉毒素的单克隆抗体1C11进行共价偶联,发现偶联前后量子点的荧光光谱变化趋势一致,而且偶联后均保持了较好的荧光特性,因此均可作为黄曲霉毒素免疫检测的探针,且与抗体偶联后的碳量子点的荧光特性优于石墨烯量子点。     

Surface modification of PET film and fabric by oligo-chitosan treatment

Poly(ethylene terephthalate) (PET) films, comprising surfaces hydrolyzed with caustic soda solution to incorporate the functional groups of carboxylic acids, were treated with a solution containing chitosan oligomer, a cross-linking agent, and a catalyst in order to modify various surface characteristics, including hydrophilicity and anti-staticity. Chitosan oligomers were prepared by depolymerizing chitosan with sodium nitrite. The chitosan molecules were fixed to the PET film surface by the reaction between the carboxylic groups in the PET film and the amino groups of the chitosan molecules. FT-IR(ATR) spectra, surface free energies, anti-staticity and other properties were measured and interpreted in relation to the structural change that was induced in the PET films by these treatments. In addition, we investigated the effect of chitosan oligomer treatment on the handle of polyester fabrics by using Kawabata evaluation system. The hydrophilic and anti-static properties of the PET film were highly improved by alkaline hydrolysis and low-molecular-weight chitosan treatment. The handle of PET fabric was gradually hardened by chitosan treatment with increasing the concentration of chitosan.     

Rheological properties of kafirin and zein prolamins

The possibility of forming dough from kafirin was investigated and laboratory prepared kafirin was formed into a viscoelastic dough system. Measurements with Contraction Flow showed that dough systems prepared from kafirin and from commercial zein had the required extensional rheological properties for baking of leavened bread. The extensional viscosity and strain hardening of the kafirin and zein dough systems were similar to those of gluten and wheat flour doughs. The kafirin dough system, however, unlike the zein dough system rapidly became very stiff. The stiffening behaviour of the kafirin dough system was presumed to be caused by cross-linking of kafirin monomers. SDS-PAGE showed that the kafirin essentially only contained α- and γ-kafirin, whereas the zein essentially only contained α-zein. Since γ-kafirin contains more cysteine residues than the α-prolamin it is more likely to form disulphide cross-links, which probably caused the differences in stiffening behaviour between kafirin and zein dough systems. Overall the kafirin dough system displayed rheological properties sufficient for baking of porous bread. Kafirin like zein appears to have promising properties for making non-gluten leavened doughs.     

Ethanolic extraction of zein from maize

Zein can be extracted from maize (Zea mays) using ethanol solutions, and recovered from the extract by diluting with water. Dilution to 40% ethanol will precipitate a mixture of zein and maize lipid with ∼15% lipid. For possible zein applications, such as film production, purer zein is required. Most of the lipid can be removed from the precipitate by selective re-extraction with hexane or ethanol, but this is expensive. A precipitate containing 90% or more of the protein in the extract, with less than 10% lipid, can be obtained by diluting the extract in stages. An initial dilution will precipitate a solid with 75% or more lipid, this precipitate can be centrifuged from the extract and the centrifugate diluted to precipitate a solid of 70% or more zein. The mass and composition of solid centrifuged from a maize extract that was diluted in several steps to characterize the composition of precipitates so formed. The lipid content of a zein product precipitated from an extract diluted from 55% ethanol to 50% is significantly lower than the content of precipitate of an extract diluted in a single step to 40% ethanol.     

Impact of different isolation procedures on the functionality of zein and kafirin

Commercial corn prolamin (zein) aggregates in water at elevated temperatures into an extensible, viscoelastic gluten-like substance. This specific functionality of zein can be used in the production of gluten-free bread from true dough systems and not from batters. The present study examined laboratory-scale isolation of such functional zein from dry milled corn. RP-HPLC indicated that successful isolation procedures resulted in relatively pure α-zeins, with a maximum ratio of (β + γ)/α-zeins of about 10%. In the present study, such functional zeins were obtained by using 70% ethanol as the extractant, without added alkali or reducing agent in the main extraction step. In contrast, films could be cast from a wider range of zein isolates, also with higher ratios of (β + γ)/α-zeins. Isolation of the analogous prolamin (kafirin) from dry milled sorghum required a more hydrophobic extractant such as 83% isopropanol to achieve partial functionality. Such kafirin was able to aggregate in warm water, preferably when a reducing agent was added; however, it quickly became firm and lost its extensibility. The present study suggests that hydrophobic interactions rather than disulfide bonds are the key to gluten-like functionality of zein and kafirin.     

Removal of surface lipids improves the functionality of commercial zein in viscoelastic zein-starch dough for gluten-free breadmaking

Maize prolamin (zein), together with starch, hydroxypropyl methylcellulose, sugar, salt, yeast and water can form wheat-like cohesive, extensible, viscoelastic dough when mixed above room temperature (e.g. 40 °C). This dough is capable of holding gas. However, it is excessively extensible, and when used for hearth-type rolls, it tends to become flat. Bench-scale defatting of zein with chloroform at room temperature significantly (P < 0.05) improved specific volume (4.5 ml/g vs. 3.3 ml/g) and shape of the rolls (width-to-height 2.0 vs. 3.9). The total lipid content determined by accelerated solvent extraction (100 °C, 69 bar, chloroform), however, only decreased from 8.0 to 6.6% due to this bench-scale defatting. Staining experiments with Naphthol Blue Black suggested that bench-scale defatting removed surface lipids from the zein particles, and thus facilitated their aggregation. Aggregation experiments with zein and water at 40 °C, and laser scanning confocal microscopy with zein-starch dough confirmed that zein particles aggregated more easily when surface-defatted. Dynamic oscillatory temperature sweeps demonstrated that surface-defatting lowered the temperature at which protein cross-linking occurred by 2 °C. This research can help to produce superior gluten-free bread and could also possibly contribute to the better understanding of wheat dough.     

Slow digestion property of microencapsulated normal corn starch

Starch is the main glycemic dietary carbohydrate, and its nutritional quality is associated with the amount of slowly digestible starch (SDS) that is beneficial to glycemic control. In the current study, a microencapsulation of normal corn starch by zein protein and its slow digestion property were investigated. A significant increase of SDS and RS was shown for starch capsules (weight ratio of zein to starch: 1:6) containing plasticizers of glycerol and oleic acid after high temperature (≥70 °C) treatment. Further studies showed a substantially decreased viscosity and the formation of an amylose–lipid complex after starch gelatinization. Thus, the hydrophobic physical barrier of the zein matrix and the amylose–lipid complex might together limit the water accessibility and starch swelling leading to a dense packing of starch materials with a high amount of SDS. The acceptable sensory property makes it an ideal ingredient for specialty food preparation and glycemic control.     

EDC/NHS crosslinked electrospun regenerated tussah silk fibroin nanofiber mats

The tussah silk fibroin (TSF) nanofibers with 611 nm diameters were prepared by electrospinning with the solvent hexafluoroisopropanol (HFIP). And then, the TSF nanofibers were crosslinked by 1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide/N-Hydroxysuccinimide (EDC/NHS) crosslinking agent. The morphology and microstructure of the crosslinked TSF nanofibers were characterized by scanning electron microscopy (SEM), Fourier transforms infrared analysis (FTIR), X-ray diffraction, Instron electronic strength tester, and cell culture. After treatment with EDC/NHS crosslinking agent, the TSF nanofibers swelled and its average diameter increased from 611 to 841 nm. FTIR and X-ray diffraction results demonstrated that random coil, ??-helix, and ??-sheet co-existed in the TSF nanofiber mats, but the content of ??-sheet increased from 25.26 to 45.34 %, and the random coil content decreased from 32.47 to 24.94 %. Compared with the electrospun pure TSF nanofiber mats, the crosslinked TSF nanofiber mats exhibited a lower breaking tenacity and initial modulus, which were 5.51 MPa and 9.86 MPa, respectively. At the same time, the extension at break of the crosslinked TSF nanofiber achieved 109.38 %. In cell culture evaluation, the crosslinked TSF nanofibers were found to support cell adhesion and spreading fibroblast L373 and bone marrow mesenchymal stem cells (BMSCs), which had potential utility in a range of tissue engineering.