Effect of plasticizing sugars on water vapor permeability, surface energy and microstructure properties of zein films

Sugars are natural plasticizers for food biopolymers and zein is the most important protein of corn. In this research, sugars (fructose, galactose and glucose) were used as plasticizers and the water vapor permeability (WVP), contact angle and microstructure of the zein films were studied. The pure zein film had high WVP and adding of sugars to 0.7 g/g zein caused to decrease of WVP. Films containing galactose had the lowest WVP.All samples had the lowest contact angle with ethanol and the highest contact angle with water. The zein films containing galactose had the highest water contact angle within the plasticized films. The pure zein films and the films containing fructose had higher critical surface tension of wetting (γ_c) than the films containing glucose and galactose. Adding sugar plasticizer to zein films increased the surface tension of zein films. In the unplasticized zein films, loose structures with a lot of cavities and voids were observed. The films plasticized by fructose had smooth surface and plasticizer particles distributed throughout of the films.     

Thermal Behavior of Zein‐based Biodegradable Films

In previous work, zein was plasticized with oleic acid to obtain flexible films. However, it was observed that film properties were affected by the preparation method employed. Our objective was to investigate the effect of processing methods on thermal behavior of zein films by differential scanning calorimetry (DSC). Films containing 41% oleic acid were prepared by casting ethanol solutions of its components on flat surfaces or by extrusion of zein resins prepared by cold water precipitation of ethanol solutions of zein and oleic acid. Extrusion was carried out in single‐screw or twin‐screw extruders. Zein films were finished by hot rolling or heated in a Carver press. DSC thermograms showed large oleic acid melting peaks for cast films, smaller peaks for resin films, and no apparent peaks for heat‐treated samples. It was suggested that the resin formation process enhanced zein‐oleic acid interactions and promoted plasticization. All samples showed glass transitions at low temperatures.     

Incorporation of partially purified hen egg white lysozyme into zein films for antimicrobial food packaging

Lysozyme, partially purified from hen egg white by precipitation of non-enzyme protein with ethanol and lyophilized after dialysis, was incorporated into zein films. The recovery and specific activity of the enzyme after partial purification varied between 45% and 72% and 2173 and 3448 U/mg, whereas the activity of the lyophilized enzyme varied between 2900 and 3351 U/mg. The partially purified enzyme was very stable and lost almost no activity in lyophilized form or in zein films stored at −18 and 4 °C for up to 8 and 4 months, respectively. During partial purification and in zein film preparation, ethanol treatment caused 123–137% and 132–315% activation of the enzyme, respectively. In zein films incorporated with 187–1318 U/cm² (63–455 μg/cm²) lysozyme, the release rates at 4 °C, changed between 7 and 29 U/cm²/min, increased at high lysozyme concentrations. Zein films incorporated with partially purified lysozyme showed antimicrobial effect on Bacillus subtilis and Lactobacillus plantarum. By the addition of disodium EDTA, the films also became effective on Escherichia coli. The results of this study showed that the partially purified lysozyme may be used in antimicrobial packaging to increase food safety.     

Wettability, surface microstructure and mechanical properties of films based on phosphorus oxychloride-treated zein

BACKGROUND: Zein, the predominant protein in corn, has been extensively studied as an alternative packaging material in edible and biodegradable films. However, films made from 100% zein are brittle under normal conditions. The aim of this investigation was to improve the film‐forming properties of zein by chemical phosphorylation. The surface hydrophobicity, surface microstructure and mechanical properties of films based on untreated and phosphorus oxychloride (POCl₃)‐treated zein were evaluated and compared. The effect of POCl₃ treatment on the rheological properties of zein solutions was also studied. RESULTS: POCl₃ treatment, especially at pH 7 and 9, led to an increase in the apparent viscosity of zein solutions. Atomic force microscopy (AFM) analysis showed that the film based on POCl₃‐treated zein at pH 7 had a stone‐like surface microstructure with a higher roughness (R_q) than the untreated zein film. The AFM data may partially account for the phenomenon that this film exhibited high surface hydrophobicity (H₀). POCl₃ treatment diminished the tensile strength (TS) of zein films from 4.83–6.67 to 1.3–2.29 MPa. However, the elongation at break (EAB) of the films at pH 7 and 9 increased from 3.0–4.5% (control film) to 150.1–122.7% (POCl₃‐treated film), indicating the potential application of zein films in wrapping foods or in non‐food industries such as sugar, fruit or troche that need good extension packing materials. CONCLUSION: The data presented suggest that the properties of zein films could be modulated by chemical phosphorylation treatment with POCl₃ at an appropriate pH value. Copyright © 2011 Society of Chemical Industry     

In situ tensile deformation of zein films with plasticizers and filler materials

Material deformation is a dynamic process. Visualisation of this deformation can help to understand the local deformation and fracture behaviour. Zein (the prolamin protein from maize) films with different amount of plasticizers (0–25%) and different filler materials (maize oil, Dimodan^®, Vestosint^®, at 25% (w/w) to protein) were deformed under tension and observed at micron scale in real time by a confocal laser scanning microscope (CLSM). The addition of plasticizers increased strain and decreased stress of zein films. At low level of plasticizers (6.25% and 12%), zein films deformed and fracture through micro-crack formation and propagation normal the tensile axis. At high Plasticization, only micro-pores were observed during tensile deformation. The filler material oil and Dimodan^® increased, but Vestosint^® decreased tensile strain in comparison to the control. This shows that the fracture dynamic is affected by the filler materials and is indeed observed by the CLSM. Analysis of local strain by Fluospheres^® as particle tracking showed a good linear correlation with the tensile strain of the plasticized zein films. The local strains of filler materials and zein matrix in the films were different from the overall tensile strain. The combination of CLSM with a fluospheres^® as particle tracking is a good method to study local deformation in biomaterials to understand the deformation and fracture behaviour of biomaterials.     

油酸与甘油对玉米醇溶蛋白膜机械性能的影响及机理探讨

主要研究了两种性质不同的增塑剂(油酸和甘油)对玉米醇溶蛋白(zein)膜机械性能的影响和可能的机理,以抗拉伸强度(TS)、伸长率(E)、透水率(WVP)为指标,结果发现油酸和甘油都能显著改善zein膜的机械性能,且添加量都以20%(g/g zein)最优;复合增塑研究发现,当添加20%混合增塑液对zein膜进行增塑时,以油酸∶甘油为3∶1复合增塑的效果最好,其中与未增塑的zein膜相比,TS提高190%,E提高70%。进一步统计学分析表明,油酸与甘油在对zein膜增塑时有正协同作用。对未增塑、20%油酸增塑、20%甘油增塑及20%复合增塑(油酸∶甘油为3∶1)zein膜的玻璃态转化温度(Tg)及红外光谱(FT-IR)分析发现,增塑后的zein膜Tg有所下降,其中复合增塑降幅最大;FT-IR图谱分析发现,复合增塑时甘油的特征峰向高波长方向移动,显示增塑作用加强;蛋白二级结构分析发现,复合增塑后,二级结构虽有小幅改变,但并未达到显著水平,因此增塑剂与zein之间的非共价键相互作用(疏水力和氢键)可能是其增塑的化学基础。     

Characteristics of edible films made from dairy proteins and zein hydrolysate cross-linked with transglutaminase

The main objectives of this research were to develop whey protein or casein films incorporating zein hydrolysate and also cross‐linked by transglutaminase as to well as characterize the physical and mechanical properties of the film. Zein hydrolysate decreased the solubility of the whey protein film (P < 0.05), while treatment with transglutaminase did not change the solubility of the film significantly. Electrophoresis patterns demonstrated that casein molecules were cross‐linked by transglutaminase and the extent of this cross‐linkage was further increased when zein hydrolysate was added. In addition, the use of zein hydrolysate decreased the tensile strength of the whey protein film by 35–45%. The elongation of the casein film was increased by 41% because of the action of transglutaminase and zein hydrolysate (P < 0.05). The water vapour permeability of the films was not significantly different. As the addition of zein hydrolysate and treatment with transglutaminase improved the flexibility of the films, the level of plasticizer required to maintain film flexibility could be reduced without sacrificing their water vapour permeability.     

不同相对湿度环境条件下玉米醇溶蛋白膜的稳定性研究

以不同蛋白浓度、甘油添加量和成膜温度制备玉米醇溶蛋白膜,研究其在不同相对湿度(RH)条件下24 d储藏过程中的机械性能变化。结果表明:不同条件下制备的玉米醇溶蛋白膜,在中低相对湿度(34%、43%、54%)条件下24 d的储藏过程中,膜的抗拉强度(TS)呈现先增加后减少的趋势,而断裂延伸率(EB)则呈现先减少后增加的趋势。而在80%的高湿度环境中,不同蛋白浓度和不同成膜温度制备的蛋白膜,储藏期间TS呈现逐渐增加的趋势,EB则快速减少;不同甘油含量的膜,在RH80%环境中TS和EB的变化趋势与RH34%、RH43%和RH54%一致。RH65%环境条件下蛋白膜的机械性能的变化受成膜条件的影响较大。整体上看,储藏过程中环境湿度对玉米醇溶蛋白膜的机械性能的影响大于制备条件的影响。因此,在蛋白膜的研究中,应用的环境湿度也是需要考察的重要因素之一。     

Antimicrobial and antioxidant activity of edible zein films incorporated with lysozyme,albumin proteins and disodium EDTA

In this study, partially purified lysozyme was incorporated into zein films in combination with chickpea albumin extract (CPAE), bovine serum albumin (BSA) and disodium EDTA. The zein films showed an inherent free radical scavenging activity. Incorporation of lysozyme did not contribute to soluble free radical scavenging activity of zein films. However, the incorporation of lysozyme in combination with CPAE increased the soluble and immobilized free radical scavenging activity of zein films 17% to 25% and almost 84%, respectively. The incorporation of CPAE also improved the distribution of partially purified lysozyme preparation in zein films and enabled the controlled release of lysozyme by reducing its release rate from zein films between 1.5- and 3.5-fold, depending on the concentration of incorporated CPAE. In contrast, the BSA incorporation made distribution of lysozyme more heterogeneous and it did not contribute to the free radical scavenging activity of films significantly. The combinational incorporation of partially purified lysozyme with disodium EDTA · 2H₂O or CPAE and disodium EDTA · 2H₂O gave zein films effective on Escherichia coli and Bacillus subtilis. This study clearly showed the benefits of using functional protein extracts to control lysozyme distribution and release rate and to improve antioxidant activity in zein films.     

干法糖基化改性玉米醇溶蛋白产物的物化特性及在胶囊壳中的应用

利用菊粉对玉米醇溶蛋白进行干法糖基化改性,通过SDS-PAGE凝胶电泳、热分析(DSC)、傅里叶红外和扫描电子显微镜等手段考察改性前后蛋白的变化。结果表明:SDSPAGE电泳谱图可确认玉米醇溶蛋白与菊粉进行了有效的接合;傅里叶红外分析也确认糖基化改性后,玉米醇溶蛋白以共价键的形式接入了菊粉糖分子;DSC分析所得玉米醇溶蛋白膜及其改性产物膜的变性温度分别为188.47,194.02℃;扫描电子显微镜发现改性后膜的表面更加平整,无孔洞。参照《中华人民共和国药典(2015版)》中关于明胶胶囊壳的相关检测指标,对菊粉改性的玉米醇溶蛋白产物制成胶囊壳进行测定,该产品各项指标均达到要求。     

Preparation and functional properties of fish gelatin–chitosan blend edible films

With the goal of improving the physico-chemical performance of fish gelatin-based films, composite films were prepared with increasing concentrations of chitosan (Ch) (100G:0Ch, 80G:20Ch, 70G:30Ch, 60G:40Ch and 0G:100Ch, gelatin:Ch), and some of their main physical and functional properties were characterised. The results indicated that the addition of Ch caused significant increase (p < 0.05) in the tensile strength (TS) and elastic modulus, leading to stronger films as compared with gelatin film, but significantly (p < 0.05) decreased the elongation at break. Ch drastically reduced the water vapour permeability (WVP) and solubility of gelatin films, as this decline for the blend film with a 60:40 ratio has been of about 50% (p < 0.05). The light barrier measurements present low values of transparency at 600 nm of the gelatin–chitosan films, indicating that films are very transparent while they have excellent barrier properties against UV light. The structural properties investigated by FTIR and DSC showed a clear interaction between fish gelatin and Ch, forming a new material with enhanced mechanical properties.     

Kefiran films plasticized with sugars and polyols: water vapor barrier and mechanical properties in relation to their microstructure analyzed by ATR/FT-IR spectroscopy

Kefiran, an exopolysaccharide produced by microorganisms present in kefir grains, is a glucogalactan that has several health promoting properties. In the present work the effect of different sugars (glucose, galactose, sucrose) and polyols (glycerol and sorbitol) as plasticizers on kefiran film properties was evaluated. Kefiran films were brittle and rigid and all the tested plasticizers improved film properties. They were all transparent with low opacity. Unplasticized kefiran films X-ray diffraction patterns were similar to those of plasticized ones, showing an amorphous-crystalline structure with low crystallinity degree. All films presented low a_w values (below 0.5) conferring protection properties against microorganism growth. The lowest permeability value was obtained with glucose as plasticizer whereas the best mechanical properties were obtained with glycerol addition.     

Antioxidant activity of Maillard reaction products from a porcine plasma protein–sugar model system

Maillard reaction products (MRPs) were prepared by heating 2% porcine plasma protein (PPP) and reducing sugars (glucose, fructose and galactose) at the levels of 1% or 2% at 100 °C up to 5 h without pH control. Browning and intermediate products, as monitored by absorbance at 420 nm and absorbance at 294 nm, increased as heating time increased (P < 0.05). However, fluorescence (Ex 347 and Em 415 nm) sharply increased within 1 h and subsequently decreased when heating time increased (P < 0.05). Increase in browning and formation of intermediate products was observed with a concomitant decrease in free amino groups. Among sugars and concentrations used, galactose at 2% rendered the highest browning and intermediate products. MRPs derived from galactose, especially at a level of 2% possessed greater reducing power and DPPH radical-scavenging activity than those prepared from fructose and glucose. MRPs derived from fructose or galactose at the level of 2% showed the increase in reducing power and DPPH radical-scavenging activity in a concentration-dependent manner. In general, antioxidative activity of PPP–sugar MRPs was coincidental with the browning development and the formation of intermediate products.     

Oxygen permeability and mechanical properties of banana films

Banana flour, obtained from banana cv. Kluai Namwa, was used to form banana films. The effect of banana flour, glycerol (Gly) and pectin content on film oxygen permeability (OP) and mechanical properties of banana films were studied. Banana flour content significantly affected film OP; whereas, Gly and pectin contents did not significantly affect film OP. Increasing banana flour and pectin contents enhanced film strength; thus, it showed higher film elastic modulus (EM) and tensile strength (TS) but less film % elongation (% E) (p ⩽ 0.05). In contrast, increasing Gly content reduced the film strength and improved film flexibility; therefore, it decreased film EM and TS but increased film % E (p ⩽ 0.05). Banana films showed good sealability, which can make these films suitable as sachets or pouches for dry foods, thus reducing the need for plastic materials.     

基于黄原胶糖基化改性玉米醇溶蛋白胶囊壁材的性能研究

目的 通过黄原胶糖基化改性玉米醇溶蛋白(Zein)提升胶囊壁材的抗拉强度、阻隔性能及肠溶性。方法 以Zein为原料,黄原胶作为羰基供体,进行干法糖基化反应,得到玉米醇溶蛋白-黄原胶改性产物(zein xanthan gum conjugates,Zein-xg),将其制备成膜,并通过机械性能、阻隔性能等指标研究糖基化改性对膜的性能的影响,考察胶囊壳外观性状、干燥失重、松紧度、炽灼残渣、脆碎度指标,并进行模拟体外释放研究。结果 与玉米醇溶蛋白相比,玉米醇溶蛋白-黄原胶膜的抗拉强度提高至21.59 MPa,提高了3.6倍,水蒸气透过系数提高了34.79%,过氧化值降低19.51%,吸水率由45.70%升高至47.03%,透油系数为0 g·mm/(cm²·d)。在模拟胃液中胶囊壳装载的小分子罗丹明B和大分子牛血清白蛋白3 h累积释放率为0,转至肠液累积释放率分别达到了98.03%和77.14%。结论 改性后的玉米醇溶蛋白-黄原胶膜的机械性能、阻隔性能等均得到显著改善。改性后的胶囊壳外观性状、干燥失重、松紧度、炽灼残渣、脆碎度等指标均符合《中华人民共和国药典(第四部)》(...     

Effects of various plasticizers and nanoclays on the mechanical properties of red algae film

To manufacture red algae (RA) film, we used various plasticizers such as glycerol, sorbitol, sucrose, fructose, and polypropylene glycol (PPG), and then determined the mechanical properties of the RA films. The tensile strength (TS), elongation at break (E), and water vapor permeability (WVP) of the films containing various plasticizers ranged between 0.43 to 9.10 MPa, 10.93% to 47.17%, and 1.28 to 1.42 ng m/m2sPa, respectively. RA films containing fructose as a plasticizer had the best mechanical properties of all the films evaluated. Incorporation of nanoclay (Cloisite Na+ and 30B) improved the mechanical properties of the films. RA film with 3% Cloisite Na+ had a TS of 10.89, while RA film with 30B had a TS of 10.85 MPa; these films also had better E and WVP values than the other RA films evaluated. These results suggest that RA/nanoclay composite films are suitable for use as food packaging materials. PRACTICAL APPLICATION: Edible RE/nanoclay composite films prepared in the present investigation can be applied in food packaging.     

Improved water resistance in edible zein films and composites for biodegradable food packaging

Zein, corn prolamine, was dissolved in several organic solvents to make films and their properties were examined. Ethanol with 20% water and acetone with 30% water were found to dissolve zein well and transform it into a transparent flexible film after moderate drying. Both films showed similar breaking strength to that of commercial thin film of polyvinylidene chloride for food use and were digested with proteases. Only the film prepared from acetone solution showed a relatively low water permeability. This water permeation was found to depend strongly on the rate of diffusion. 1,2-Epoxy-3-chloropropane (ECP) was added into the acetone solution to cross-link the zein molecules for the purpose of improving the breaking strength and water-resistant properties of the film. Alpha-chymotrypsin was found to digest the film even after the modification with ECP. However, this cross-linking resulted in little improvement in the water-resistant properties of the film and also reduced its flexibility.     

Effect of hydrophobic plasticizers on functional properties of gelatin-based films

The aim of this study was the production and characterization of gelatin-based films using hydrophobic plasticizers derived from citric acid and soy lecithin as emulsifier. The films were characterized as to their mechanic properties, permeability to water vapor, opacity, morphology and possible interactions using Fourier transform infrared spectroscopy. Tensile strength values (TS) varied from 36 to 103 MPa, however, the increase in the concentration of plasticizers (acetyltributyl citrate and tributyl citrate) reduced TS by 57% and no relation was observed between plasticizer quantities and the elongation in the quantities tested. Permeability to water vapor varied between 0.17 and 0.34 (g mm/m² h kPa), slightly increasing with the increase in concentration of plasticizers. The effectiveness in the use of soy lecithin emulsifier in the homogenization between the compounds could be proven by microscopic observation using confocal laser microscopy.     

Flow properties of corn starch–milk–sugar system prepared at 368.15 K

The rheological properties of corn starch–milk–sugar (CMS) paste were investigated using a concentric cylinder viscometer. Three types of sugars, namely, glucose, fructose and sucrose were used to prepare the paste. The paste was prepared at three different starch concentrations, 2, 4 and 6 wt.%, while the sugar concentrations of the three types were varied up to 16 wt.%. Milk with three different fat contents was used in preparation of the CMS paste. At constant starch and sugar concentrations and using skim milk, glucose was found to have the largest effect on the apparent viscosity of the CMS past. On the other hand, the fructose has the lowest effect on the CMS paste viscosity. It was also demonstrated that the pastes prepared with full cream milk have higher viscosity than the ones prepared using skim milk. The rheological CMS paste properties were modelled using Herschel–Bulkley model. The model was adequate and accurate.     

Edible films produced with gelatin and casein cross-linked with transglutaminase

In this study, transglutaminase was used to produce cross-linked casein, gelatin and casein–gelatin blend (100:0, 75:25, 50:50, 25:75 and 0:100) edible films. Cross-linking was investigated by SDS–PAGE. Mechanical and water vapor barrier properties of the films were characterized using ASTM procedures, and the film morphology was evaluated using scanning electron microscopy. The casein–gelatin film showed significant greater elongation values (P < 0.05) with or without transglutaminase treatment, as compared to films made from gelatin or casein alone. Mixtures of casein and gelatin produced a synergistic effect only observed in the film elongation, while no improvement was detected for tensile strength and water vapor barrier properties, except for the casein:gelatin (75:25) formulation with transglutaminase, which showed the lowest water vapor permeability value (5.06 ± 0.31 g mm/m² d kPa). Enzymatic cross-linking also induced a substantial increase in the high molecular weight protein components in the film forming solutions.