Physical and Molecular Properties of Wheat Gluten Films Cast from Heated Film-Forming Solutions

The effect of heating film-forming solutions on physical and molecular properties of cast wheat gluten (WG) films was determined. Glycerol-plasticized films were cast from alkaline (pH 10), heat-treated (55,75, or 95°C for 10 min) solutions of WG in aqueous ethanol. Protein solubility (PS) of films in water decreased (P<0.05) with increasing temperature. Gel permeation chromatograms showed reduced extractability of protein fractions other than ω-gliadins in WG films. This reduced extractability was due to disulfide (S-S) bond formation. SDS-PAGE patterns of native WG and WG film samples suggested increased cross-linking through covalent S-S bonds in films from solutions heated at 75 or 95°C. Water resistance in potential packaging applications of WG edible films could be modified by adjusting heat-treating temperature.     

EDC和NHS对玉米醇溶蛋白成膜性质的影响

为提高玉米醇溶蛋白膜的抗拉强度和伸长率,降低其水蒸气透过率和吸水率,研究交联剂1-乙基-3-（3-二甲基氨丙基）碳二亚胺盐酸盐（EDC）和N-羟基琥珀酰亚胺（NHS）对成膜性质的影响。结果表明：以90%乙醇为溶剂,EDC和NHS的添加量分别为0.06 g/g时,制得的膜性能最佳,抗拉强度为83 MPa,较未添加交联剂的蛋白膜提高97.6%;伸长率为5.5%,提高57.1%;水蒸气透过率为2.5×10-8（g·m）/（m2·h·Pa）,降低43.2%;吸水率为39.4%,降低24.4%;质量损失率为3.6%,增加20.0%;静态接触角为67.4°,表明膜表面仍为疏水表面。原子力显微镜观测显示,加入交联剂后,蛋白分子聚集体变小,以均一的小球型聚集体形式紧密有序排列。     

The water vapour permeability,mechanical properties and solubility of fish gelatin–chitosan films modified with transglutaminase or 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and plasticized with glycerol

The effect of glycerol on the mechanical and water barrier properties, as well as on the water solubility, of fish gelatin–chitosan films (4:1, w/w) cross-linked with TGase or EDC was determined. The addition of glycerol in concentrations up to 30% (of the substrate mass) to the fish gelatin–chitosan films modified with TGase or EDC did not change their solubility in buffers of pH 3 and 6 at 25 °C or during heating at 100 °C for 60 min. The chemical and enzymatic cross-linking of the components did not increase the water barrier properties of the films. WVP of the films modified with EDC and TGase was not affected by glycerol at concentrations up to 25% of the substrate mass. Tensile strength of the films decreased after modification of the components with TGase or EDC, respectively, by about 25% and 40%. The elongations of the enzymatically modified films containing 20% of glycerol and of chemically modified films containing 15% of glycerol were, respectively, about 8 and 13 times higher than those of unplasticized films; however, the tensile strengths of plasticized films were, respectively, 2.5 and 5 times lower.     

Effect of thermo-pressing temperature on the functional properties of bioplastics made from a renewable wheat gliadin resin

In this work a new methodology based on thermo-pressing a resin made from gliadins and glycerol has been developed to obtain water resistant films. The effect of processing temperature was studied on the functional properties of the films. The results of SDS-PAGE analysis of the molecular weight profiles of the resulting films were indicative of disulfide/sulfhydryl interchange reactions giving rise to the formation of intermolecular disulfide bonds between the gliadin units. These reactions augmented the degree of cross-linking of the matrix, which increased with thermo-pressing temperature, as evidenced by the residual reaction enthalpy values determined by MDSC as well as by cross-linking density values determined from tensile tests. In consequence the films produced at high temperature had better water resistance upon immersion, greater maximum tensile strength and Young's modulus values, and lower water vapor and oxygen permeabilities compared with cast films. Based on the analytical test results, thermo-pressing the resin in successive time/force steps along with a temperature of 130 °C produced gliadin films with improved properties.     

Characterizations of fish gelatin films added with gellan and κ-carrageenan

Fish gelatin is known to be inferior to mammalian gelatins. Gellan and κ-carrageenan were added to improve properties of the fish gelatin films. Initially, polysaccharides were added to make fish gelatin gels, and tested for the melting point. Mechanical, barrier, color and microstructure properties, as well as Fourier transform infrared (FTIR) and thermal analysis (DSC) of the modified fish gelatin films were evaluated. The addition of gellan and κ-carrageenan increased the melting point of fish gelatin gels, gellan being more effective. Polysaccharides modified fish gelatin films by increasing tensile strength and barrier against water vapor, but made films slightly darker. Scanning electron microscopy (SEM) microstructure analysis revealed that gellan eliminated cracks present in the film matrix resulting in a more uniform structure. FTIR and DSC analyses showed that both polysaccharides effectively interacted with fish gelatin, and moreover, gellan being more effective. Overall, addition of gellan up to 2 g/100 g of gelatin performed better in enhancing fish gelatin films properties.     

魔芋葡甘聚糖/油酸修饰纳米ZnO复合抗菌膜的制备与表征

为提高纳米氧化锌（ZnO）在魔芋葡甘聚糖（konjac glucomannan，KGM）中的分散性，以增强纳米复合膜的抗紫外线性能和抗菌性能，通过油酸（oleic acid，OA）对纳米ZnO进行修饰，制备OAZnO溶液，并采用浇铸法制备KGM/OAZnO纳米复合膜，通过流变学分析、傅里叶变换红外光谱分析、X射线衍射分析、微观结构观察、热重分析以及理化性质测定，研究OAZnO的添加对KGM膜结构和理化性质的影响。结果表明，OA提高了纳米ZnO的分散性，傅里叶变换红外光谱分析证实纳米ZnO与KGM分子间形成了较强的氢键，X射线衍射光谱结果表明纳米ZnO中的Zn2＋与KGM链上的—OH形成配位键；同时，适量OAZnO（0.49 mL）使纳米复合膜包装机械性能和阻水性能得到增强，其水蒸气透过率较KGM膜降低了35.62%，拉伸强度提高了79.26%。此外，紫外光谱分析和抗菌实验结果表明KGM/OAZnO纳米复合膜具有较强的紫外阻隔性能和抗菌性能。综上，OAZnO的添加可以提高纳米复合膜综合性能，且OAZnO溶液添加量为0.49 mL时最强，可以作为功能性食品包装膜。     

Effect of transglutaminase and EDC on biodegradation of fish gelatin and gelatin-chitosan films

The subject of the study was analysis of enzymatic degradation of fish gelatin and fish gelatin-chitosan films cross-linked with transglutaminase (TGase) and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC). Unmodified gelatin films were almost completely hydrolysed by trypsin and proteinase N, and in about 60% by pepsin. Gelatin films modified with TGase in concentration of 0.2 mg/ml and with EDC (30 mM) were hydrolysed by trypsin in 90–100% while by pepsin in about 40 and 25%, respectively. Fish gelatin from gelatin-chitosan films, unmodified and modified with TGase, was almost completely hydrolysed by trypsin. The presence of chitosan in two-components films cross-linked with EDC decreased hydrolysis by pepsin and trypsin, respectively, by about 65, and 20% more in comparison to that of one-component chemical modified films. Applied modifications had no significant influence on degradation of fish gelatin and gelatin-chitosan films by proteinase N.     

Effects of protein interactions on properties and microstructure of zein–gliadin composite films

Zein and gliadin are both readily dissolved in aqueous ethanol and have good film-forming property. This article describes an attempt to improve the flexibility of zein films by the addition of gliadin to the zein film-forming solution. The properties of zein–gliadin composite films, i.e., color, transparency, moisture content, water solubility, water vapor permeability, dynamic contact angle which in turn affected the mechanical property, water resistance and glass transition temperature of films were investigated. The contents of second structure were characterized via Fourier transform infrared spectroscopy (FTIR), whereas morphology of films was examined by scanning electron microscopy (SEM). It was observed that the addition of gliadin enhanced the strain at break of zein–gliadin composite films as a result of the increase in the content of α-helix, β-turn structures and decrease in the level of β-sheet structure. The water resistance of films decreased with the content of gliadin increasing. Morphology of composite films showed that gliadin and zein organized a homogeneous material. This work opens a new perspective for zein in flexible food package.     

Tensile, Solubility, and Electrophoretic Properties of Egg White Films as Affected by Surface Sulfhydryl Groups

Films plasticized with polyethylene glycol were cast from alkaline (pH 10.5, 11.0, or 11.5), aqueous egg white (EW) solutions with or without heating (40°C for 30 min). Prior to casting, concentration of surface sulfhydryl (SH) groups was determined and they increased (P < 0.05) (3.81–19.45 μM/g protein) with both pH and heating, presumably due to protein denaturation and cleavage of disulfide (S-S) bonds. Concentration of surface SH groups correlated (P < 0.05) with film tensile strength (r = 0.70), elongation at break (r = 0.86), and film total soluble matter (r =−0.94). Most likely, surface SH groups formed S-S bonds through air oxidation and/or sulfhydryl/disulfide interchange, thus contributing to EW film formation. SDS-PAGE patterns in presence or absence of 2-mercaptoethanol confirmed occurrence of S-S bonding in dried EW films.     

Improvement of the gelling ability in restructured fish products: effect of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide level and pH

The production of heat-induced gels from raw materials with poor gelling ability remains a technical challenge, for which new solutions have been proposed. The addition to the gel batters of a cross-linking chemical agent, such as 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), may present a valuable tool for the improvement of gelling. Accordingly, a response surface methodology was used to optimize the conditions of EDC application, the EDC concentration (0.0–0.5?%, w/w) and the batters’ pH (4.5–7.5). Results showed that textural, colour, and water-binding properties of heat-induced hake gels were extremely sensitive to EDC content and pH. It was possible to find an optimal EDC level-pH binary common to the various studied parameters, a pH between 4.0 and 5.0 and an EDC concentration of 0.5?%, w/w. Moreover, this experimental work proved to be feasible the achievement of gel products of acceptable textural quality from frozen hake through EDC incorporation in optimal conditions.     

Chemical composition,nutritional value and antioxidant properties of Allium caepa L. Var. tropeana (red onion) seeds

Chemical analysis of Allium caepa L. var Tropeana (red onion) seeds showed high amounts of oil (20.4%), fibre (22.4%), crude protein (24.8%), calcium (175.0 mg/100 g), potassium (1010 mg/100 g), low amounts of sodium (11.2 mg/100 g) and six cysteine derivatives, of which the S-propylmercapto-cysteine has never been reported in onion before. The antioxidant capacity of seed extracts containing cysteine derivatives (SECCD), before and after boiling the seeds, and of cooking water extracts containing cysteine derivatives (CWECCD), was also evaluated, by the ferric reducing antioxidant power (FRAP) and 1,1-diphenyl-2-picrilhydrazyl (DPPH) assays. The extracts showed discrete antioxidant capacity which increased after boiling, although cooking methods caused significant losses of the cysteine derivatives in water.     

Preparation and characterization of pullulan–chitosan and pullulan–carboxymethyl chitosan blended films

The characteristics of pullulan–chitosan and pullulan–carboxymethyl chitosan (CMCH) blended films were investigated. The viscosity of the film-forming solutions, mechanical properties, barrier properties (water and oxygen), water solubility, and color are reported. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) measurements were used to study the interactions and compatibility between the polysaccharides. The addition of the chitosan or CMCH to pullulan effectively modified the mechanical and oxygen barrier property of the film. The improvements in the film properties have been related to strong interactions between chitosan/CMCH and pullulan polymers, which were observed with FTIR spectroscopy. The ratio of pullulan and chitosan to achieve films with optimum mechanical properties, oxygen and water barrier properties was identified to be 1:1. Increased concentrations of chitosan lead to the formation of inter-molecular hydrogen bonds rather than the intra-molecular hydrogen bonds which were suggested from XRD measurements.     

小米谷蛋白及醇溶蛋白结构特征

采用碱提酸沉法提取小米谷蛋白,乙醇浸提小米醇溶蛋白,对2种蛋白的结构特征进行研究。结果表明,小米醇溶蛋白的组成较为简单,且分子量较小,而小米谷蛋白在高分子量和低分子量都有分布。XRD分析发现二者皆为无定型结构。圆二色光谱测定结果表明,小米醇溶蛋白属于全α型结构,有序性优于小米谷蛋白。另外,通过原子力显微镜观测发现,小米醇溶蛋白呈球状结构,分散状态,而小米谷蛋白分布较为密集。     

Nano-biomaterials application: Morphology and physical properties of bacterial cellulose/gelatin composites via crosslinking

Nano-scale bacterial cellulose (BC) provides a fine structural network; therefore, this study investigated alkaline treated BC/gelatin composites (ATBC/G) crosslinked with transglutaminase (ATBC/G/T), genipin (ATBC/G/G), or EDC (ATBC/G/E), to improve the mechanical strength and hydrophilic property of BC composites. The ATBC/G composites displayed increased gelatin content, moduli, and hardness with increased gelatin concentrations in the immersion solution. EDC most effectively improved the mechanical properties of ATBC/G composites. Gelatin entering ATBC network, fills the empty spaces and connects to the 3D structure of ATBC. The ATBC/G/E composites maintain a network structure under 10% gelatin concentrations because gelatin tightly attaches to the ATBC surface. The ATBC/G composite exhibited analogical crystal morphology of ATBC, however, increased gelatin concentrations in addition to the EDC treatment decreased crystallinity in the composites. The FTIR spectrograph of the ATBC/G composites revealed the OH groups of the composites tended to increase. Therefore, gelatin crosslinking disrupted the crystallization formed from the hydrogen bonds between cellulose molecules. Crosslinking can also enhance the rehydration ratio.     

单宁酸对小麦醇溶蛋白结构及功能性质的影响

采用荧光分光光度计、紫外分光光度计(UV-visible)、傅立叶红外光谱仪(FTIR)等探究单宁酸与小麦醇溶蛋白通过非共价与共价方式结合的机理以及蛋白结构与功能特性的改变。结果表明,在非共价作用下,单宁酸对小麦醇溶蛋白的淬灭类型为生成复合物的静态淬灭作用,两者以氢键作用驱动结合,且以1:1摩尔比结合。同时,在碱性环境下,单宁酸与小麦醇溶蛋白上的自由氨基发生席夫碱反应以共价方式形成复合物。此外,不同条件下,复合物的形成会使得小麦醇溶蛋白三级结构发生去折叠现象、二级结构展开。碱性环境下复合物的形成导致小麦醇溶蛋白二级结构展开程度更高。单宁酸的加入使复合物的抗氧化能力提高,且非共价复合物抗氧化活性更高。在热稳定性方面,两者共价结合使小麦醇溶蛋白的热稳定性提升1.03℃,而两者非共价结合使小麦醇溶蛋白热稳定性降低5.39℃。     

Effect of amino acids on the chemical oxidation of olive o-diphenols in model systems

Addition of certain amino acids (l-tryptophan, l-histidine, l-cysteine and l-cystine) to model solutions of caffeic acid and hydroxytyrosol (the two most characteristic o-diphenols of ripe olives) improved the dark colour obtained after oxidation. A detailed study carried out with l-cysteine and caffeic acid showed that, after an initial inhibitory effect, increasing concentrations of amino acid led to darker solutions. The same effect was also found in hydroxytyrosol solutions with increasing amounts (2–8 mm) of cysteine without lag phase, except for 10 mm level. Cysteine also produced darker colour with oxidised storage brine of ripe olives. These results open the door to a possible use of this amino acid as additive or aid in processing to produce darker and homogeneous ripe olives.     

Paste viscosity of rice starches of different amylose content and carboxymethylcellulose formed by dry heating and the physical properties of their films

Starch modified by combination with sodium carboxymethylcellulose (CMC) has been reported to have improved film properties. In this study, rice starches with different amylose content were heat-treated in a dry state after being impregnated with low or medium-viscosity CMC. Noticeable change was found in pasting properties of the starches after dry heat treatment with CMC. It indicated that crosslinkage occurred between the starch and CMC. The waxy starch showed significant change in viscosity throughout pasting after dry heating with CMC, suggesting that the ester bonds were mostly formed between the hydroxyl groups in amylopectin branches of rice starch and carboxylate acid groups of CMC. Particle size also increased after heat treatment with CMC. The modified starch-based films showed improvement in the tensile strength. Both water vapor and oxygen permeability reduced for the modified starch-based films. Dynamic mechanical analysis (DMA) study showed that the values of G′ of modified starch-based film were higher than those of native starch-based film over the temperature range −40 to 60 °C. The heating process with CMC could be used as a modification method for starch and provide desirable properties of starch-based films.     

再生丝素纤维的湿法纺丝及其交联改性研究

以六氟异丙醇(HFIP)溶解再生丝素膜,通过湿法纺丝获得再生丝素纤维。再生丝素纤维经1-(3-二甲基氨基丙基)-3-乙基碳化二亚胺(EDC)和N-羟基丁二酰亚胺(NHS)作为交联剂进行后处理,利用扫描电镜(SEM)、红外光谱(FTIR)、X-射线衍射(XRD)、DSC热分析法、力学性能等表征方法研究和分析了牵伸和交联前后纤维聚集态结构和力学性能的变化。研究结果表明:再生丝素纤维经牵伸和EDC/NHS交联改性后,纤维直径变细为87μm,纤维内部结构以silk II结构为主;纤维的热稳定性提高,热分解峰峰值由281℃提高至288℃;纤维的断裂强度和断裂伸长率明显增大,分别达到1.41 cN/dtex和11.38%,表现出良好的柔韧性。     

青稞和小麦醇溶蛋白和谷蛋白结构性质的比较研究

采用Osbron法分别提取青稞和小麦中的醇溶蛋白和谷蛋白,对这4 种蛋白质进行十二烷基硫酸钠-聚丙烯酰胺凝胶电泳（sodium dodecyl sulfate-polyacrylamide gel electrophoresis,SDS-PAGE）分析和红外光谱分析,并测定其表面疏水性、热稳定性、总巯基和二硫键含量。结果表明：醇溶蛋白在青稞蛋白质中的含量为16.96%,低于其在小麦蛋白质中的含量;谷蛋白在青稞蛋白质中的含量为47.83%,高于其在小麦蛋白质中的含量,但经SDSPAGE分析发现青稞中高分子质量谷蛋白亚基（high molecular weight glutenin subunit,HMW-GS）含量远低于小麦中的。青稞醇溶蛋白和谷蛋白中的二硫键和总巯基含量均低于小麦中的。4 种蛋白的表面疏水性差异不大。青稞谷蛋白的热稳定性高于小麦谷蛋白,不利于其吸收水分和部分展开。红外光谱分析发现小麦醇溶蛋白和青稞醇溶蛋白的二级结构主要由β-转角和β-折叠组成,而小麦醇溶蛋白中的β-转角所占比例更高;青稞谷蛋白和小麦谷蛋白的二级结构主要以β-折叠为主。     

NaCl浓度对麦醇溶蛋白与槲皮素相互作用的影响

利用荧光光谱、紫外光谱、傅里叶变换红外光谱法,研究不同NaCl浓度下麦醇溶蛋白（gliadin,G）与槲皮素（quercetin,Q）的相互作用。荧光光谱分析结果表明：不同NaCl浓度下,Q导致G荧光猝灭现象的发生,且随NaCl浓度的增大,荧光强度伴随明显蓝移现象（10?nm左右）;当Q浓度为50?μmol/L时,荧光猝灭率为96%～98%,表明两者发生强相互作用;Q对G产生静态或动、静态结合的猝灭作用;50?mmol/L?NaCl浓度下,G与Q的结合常数（Ka）和结合位点数（n）数值最大,为4.87×107?L/mol和1.477?1,说明添加适量NaCl有利于相互作用的增强。热力学数据分析结果表明：50?mmol/L?NaCl浓度下,G与Q之间主要为疏水作用力,而其他NaCl浓度下,G与Q之间主要为氢键相互作用。同步光谱和紫外光谱分析结果表明：Q改变了G中芳香族氨基酸所处的微环境,使蛋白分子构象发生变化,且色氨酸残基对蛋白固有荧光的猝灭贡献更大。傅里叶变换红外光谱和拉曼光谱分析结果表明：在特定NaCl浓度下G与Q存在特定作用方式,氢键或疏水相互作用在复合物的形成中起重要作用,蛋白质的二级、三级结构及氨基酸侧链微环境发生改变。研究结果证明,NaCl浓度影响蛋白-多酚的相互作用,添加适量NaCl有利于G和Q的结合以及蛋白质的构象变化。本研究为Q作为一种天然食品添加剂应用于小麦制品提供了理论基础和科学依据。