Physical and antimicrobial properties of chitosan–tea tree essential oil composite films

Antimicrobial films were prepared by incorporating different concentrations of tea tree essential oil (TTO) into chitosan (CH) films. Film-forming dispersions (FFD) were characterized in terms of rheological properties, particle size distribution and ζ-potential. In order to study the impact of the incorporation of TTO into the CH matrix, the water vapour permeability (WVP), mechanical and optical properties of the dry films were evaluated. The properties of the films were related with their microstructure, which was observed by SEM. Furthermore, the antimicrobial effectiveness of CH–TTO composite films against Listeria monocytogenes and Penicillium italicum was studied.     

Antimicrobial activity and mechanism of PLA/TP composite nanofibrous films

Electrospinning is conducted with polylactic acid (PLA) and tea polypheno (TP) to obtain PLA/TP composite nanofibrous films with high antimicrobial activity. An investigation of the composition, antimicrobial activity, and mechanism of these composite nanofibrous films was conducted by using infrared spectroscopy (FT-IR), inhibition zone method, fluorescence activated cell sorter (FACS), and transmission electron microscope (TEM). IR spectra results showed that TP and PLA composited well through valence bonds in PLA/TP composite nanofibrous films. Ranges of the inhibition zone for the growth of Escherichia coli (E. coli) and Staphylococcus (Staphylococcus aureus) were 3.67 and 3.71?cm in pure PLA nanofibrous films, but 5.17 and 5.67?cm in PLA/TP composite nanofibrous films, respectively. Results indicated that the antimicrobial activity of PLA/TP composite nanofibrous films were much higher than that of pure PLA nanofibrous films. Meanwhile, the antimicrobial activity against S. aureus was also slightly higher than E. coli. FACS results showed that the positive rate of PLA/TP composite nanofiber films was greater than that of pure PLA nanofibrous films, increasing from 1.45 and 0.78% to 9.26 and 6.47% against S. aureus and E. coli, respectively. The result of TEM indicated that PLA/TP composite nanofibrous films led to the death of bacteria by destroying the integrity of cell membrane.     

GEO添加量对PLA/GEO复合膜性能及双孢蘑菇保鲜效果的影响

本文研究了不同浓度（0%、5%、7.5%、10%和12.5%）的葡萄柚精油（GEO）对聚乳酸(PLA)/葡萄柚精油复合膜的热性能,结构性能,机械性能,气体阻隔性能和抗菌性能等方面的影响。GEO通过减少聚合物链段的分子间作用力,从而改善复合膜的柔韧性,对复合膜起到一定的增塑作用。GEO的添加降低了PLA相的结晶性。随着GEO浓度的增加,复合膜的水蒸汽阻隔性能显著降低。但是,复合膜的抗菌活性因GEO的加入得以提高。将聚乳酸/葡萄柚精油复合膜应用于双孢蘑菇保鲜。结果表明,聚乳酸/葡萄柚精油复合膜与纯聚乳酸膜、低密度聚乙烯膜相比较,更能有效地保持蘑菇的硬度,阻止微生物生长,维持较好的总体接受度。因此,聚乳酸/葡萄柚精油复合膜可作为一种有效的包装材料,用于延长双孢蘑菇的货架期。     

Physical and antioxidant properties of chitosan and methylcellulose based films containing resveratrol

New trends in edible films focus on the improvement of their functionality through the incorporation of active compounds, such as antimicrobial or antioxidant agents. Resveratrol is a natural antioxidant found in a variety of plant species, such as grapes, and could be used for minimizing or preventing lipid oxidation in food products, retarding the formation of oxidation products, maintaining nutritional quality and prolonging the food shelf life. The aim of this work was to develop and characterize two different polymeric composite films (made with chitosan (CH) and methylcellulose (MC)) containing different amounts of resveratrol. This compound could be incorporated efficiently into both films, but provoke structural changes in the matrices, which became less stretchable (65–70% reduction of deformation at break at the greatest resveratrol content) and resistant to fracture (26 and 54% reduction of tensile at break for MC and CH, respectively, at the greatest resveratrol content) more opaque (significant reduction of the internal transmittance) and less glossy (about 60–65% reduction of gloss at the greatest resveratrol content). Film barrier properties were hardly improved by the presence of resveratrol; water vapour and oxygen permeability tend to slightly decrease when resveratrol was incorporated into both polymers. Composite films showed antioxidant activity, which was proportional to the resveratrol concentration in the film. None of the films showed antimicrobial activity against Penicillium italicum and Botrytis cinerea. Thus, these films could be applied to food products which are sensitive to oxidative processes to prolong their shelf life.     

抗菌性无定型纳米二氧化钛/聚乳酸膜的制备及表征

溶胶-凝胶法水解异丙醇钛制备纳米二氧化钛（TiO2）溶液,进行粒径优化及表征。紫外光谱、红外光谱、X射线衍射、粒径测试结果表明制备的纳米TiO2为较高可见光利用率的无定型纳米粒子。采用溶液共混法制备聚乳酸/纳米二氧化钛（polylactic acid/nano-TiO2,PLA/nano-TiO2）复合膜,研究不同纳米TiO2质量分数对PLA/nano-TiO2复合膜的性质影响。结果表明,PLA/nano-TiO2复合膜中纳米TiO2质量分数为0.6%时拉伸强度达到最大值,为63.3 MPa,此时断裂伸长率最小,为2.3%。PLA/nano-TiO2复合膜接触角均低于纯PLA膜,从78.40°减小到72.83°;PLA/nano-TiO2复合膜的吸水率显著高于纯PLA膜,从0.56%提高为1.48%;PLA/nano-TiO2复合膜水蒸气透过率比纯PLA膜高,从3.46×10－8（g·m）/（m2·h·Pa）提高到4.66×10－8（g·m）/（m2·h·Pa）。由PLA/nano-TiO2复合膜的抑菌性实验可知,添加纳米TiO2的复合膜在紫外光照下有明显的抑菌效果。     

Functional Properties of Antimicrobial Lysozyme-Chitosan Composite Films

ABSTRACT: Lysozyme-chitosan composite films were developed for enhancing the antimicrobial properties of chitosan films. A 10% lysozyme solution was incorporated into 2% chitosan film-forming solution (FFS) at a ratio of 0%, 20%, 60%, and 100% (w lysozyme/w chitosan). Films were prepared by solvent evaporation. Lysozyme release from the film matrix, the antimicrobial activity of films against Escherichia coli and Streptococcus faecalis , and basic film properties were investigated. The lysozyme release proportionally increased with increasing initial concentration of lysozyme in the film matrix, and the amount of released lysozyme was in natural log relationship with time. The films with 60% lysozyme incorporation enhanced the inhibition efficacy of chitosan films against both S. faecalis and E. coli , where 3.8 log cycles reduction in S. faecalis and 2.7 log cycles reduction in E. coli were achieved. Water vapor permeability of the chitosan films was not affected by lysozyme incorporation, whereas the tensile strength and percent elongation values decreased with increased lysozyme concentration. Scanning electron microscopy images revealed that lysozyme was homogeneously distributed throughout the film matrix. This study demonstrated that enhanced antimicrobial activity of lysozyme-chitosan composite films can be achieved by incorporating lysozyme into chitosan, thus broadening their applications in ensuring food quality and safety.     

抗菌性玉米醇溶蛋白/壳聚糖复合膜的制备与性质

采用分步法,先配制壳聚糖/醋酸/乙醇溶液体系,再向其中加入玉米醇溶蛋白,最后利用流延法制成玉米醇溶蛋白/壳聚糖(zein/chitosan,Z/C)复合膜,探讨壳聚糖质量分数对Z/C复合膜理化性质与抗菌特性的影响。结果表明:在壳聚糖质量分数为2%~8%范围内,混合溶液的黏度和电导率随壳聚糖质量分数变化成阶梯状变化,且壳聚糖的添加对复合膜性质有显著影响,Z/C复合膜的断后伸长率从1.00%提高到6.67%,接触角从65.97°减小到53.61°,水蒸气透过率从5.23 g·m/(m2·h·Pa)提高到9.16 g·m/(m2·h·Pa);扫描电子显微镜观察,复合后薄膜保持光滑、均一;大肠杆菌抑菌实验表明添加壳聚糖使复合膜具有较强的抗菌特性。     

Characterization of chitosan–oleic acid composite films

Edible films based on high molecular weight chitosan (CH) and different concentrations of oleic acid (OA) were prepared. Film-forming dispersions (FFD) were characterized in terms of rheological properties, surface tension, particle size distribution and ζ-potential. In order to study the impact of the incorporation of OA into the CH matrix, the water sorption isotherms, water vapour permeability (WVP), mechanical properties, and optical properties of the dry films were evaluated. Results showed that the increase in OA promoted changes in the size and surface charge of the FFD particles, which had an impact on the rheological properties of the FFD. As regards the film properties, the higher the OA content, the lower the WVP and the moisture sorption capacity. In general, the addition of OA into the CH matrix leads to a significant increase in gloss and translucency and a decrease in the tensile strength, elongation at break and elastic modulus of the composite films. The mechanical and optical properties of the films were related with their microstructure, which was observed by SEM.     

抗菌肽BCp12保鲜膜在乳扇贮藏保鲜中的应用

为延长乳扇的货架期,以酪蛋白、壳聚糖为原料包裹抗菌肽BCp12制备复合保鲜膜。采用单因素试验和正交试验确定最佳制备工艺,以膜的断裂伸长率、拉伸强度及抑菌活性为指标,结合扫描电子显微镜（scanning electron microscopy,SEM）、傅里叶变换红外光谱（Fourier transform infrared spectroscopy,FT-IR）及分子对接探究复合膜的形成机理,并将其应用于乳扇保鲜。结果表明,可食膜的最佳制备工艺为酪蛋白/壳聚糖质量比1∶1.5、BCp12质量浓度1 mg/mL、甘油质量分数1.5%、干燥温度55℃。SEM观察结果显示复合膜具有良好的相容性;FT-IR分析结果显示1 545.67 cm-1处为C—O伸缩振动吸收峰且结构稳定;分子对接结果表明BCp12与酪蛋白、壳聚糖之间主要通过残基Y4与—NH2活性位点产生氢键相互作用。与对照组相比,BCp12膜组乳扇的过氧化值变化较慢且经4℃贮藏后可使保质期延长60 d。综上,该膜能抑制腐败菌的生长,本实验可为BCp12/壳聚糖/酪蛋白复合膜的应用开发提供一定的技术参考。     

壳聚糖/微晶甾醇可食性复合膜的制备、性能及结构表征

以壳聚糖为成膜基质,添加具有抗氧化和抑菌作用的植物甾醇,采用流延法制备壳聚糖/微晶甾醇可食性复合膜,旨在赋予壳聚糖膜抗氧化活性及提高其抑菌性。当甾醇添加量分别为壳聚糖质量的0%~12%时,随着添加比例的增加,复合膜的拉伸强度和断裂伸长率逐渐下降,溶解度和溶胀度逐渐增加,水蒸气透过系数显著降低,对超氧阴离子自由基(O_2~-·)及羟自由基(·OH)的清除率显著提高,对金黄色葡萄球菌和大肠杆菌的抑菌性能明显增强;采用红外光谱、扫描电子显微镜、X射线衍射和热重分析表征了复合膜的相容性。结果表明:甾醇添加量为9%的壳聚糖/微晶甾醇可食性复合膜各项性能指标良好,且壳聚糖与甾醇分子之间形成了分子间氢键,有较强的相互作用,整个共混体系的相容性良好。     

Effects of gelatin origin,bovine-hide and tuna-skin,on the properties of compound gelatin–chitosan films

With the purpose to improve the physico-chemical performance of plain gelatin and chitosan films, compound gelatin–chitosan films were prepared. The effect of the gelatin origin (commercial bovine-hide gelatin and laboratory-made tuna-skin gelatin) on the physico-chemical properties of films was studied. The dynamic viscoelastic properties (elastic modulus G′, viscous modulus, G″ and phase angle) of the film-forming solutions upon cooling and subsequent heating revealed that the interactions between gelatin and chitosan were stronger in the blends made with tuna-skin gelatin than in the blends made with bovine-hide gelatin. As a result, the fish gelatin–chitosan films were more water resistant (∼18% water solubility for tuna vs 30% for bovine) and more deformable (∼68% breaking deformation for tuna vs 11% for bovine) than the bovine gelatin–chitosan films. The breaking strength of gelatin–chitosan films, whatever the gelatin origin, was higher than that of plain gelatin films. Bovine gelatin–chitosan films showed a significant lower water vapour permeability (WVP) than the corresponding plain films, whereas tuna gelatin–chitosan ones were only significantly less permeable than plain chitosan film. Complex gelatin–chitosan films behaved at room temperature as rubbery semicrystalline materials. In spite of gelatin–chitosan interactions, all the chitosan-containing films exhibited antimicrobial activity against Staphylococcus aureus, a relevant food poisoning. Mixing gelatin and chitosan may be a means to improve the physico-chemical performance of gelatin and chitosan plain films, especially when using fish gelatin, without altering the antimicrobial properties.     

Physical and antimicrobial properties of banana flour/chitosan biodegradable and self sealing films used for preserving Fresh-cut vegetables

Kluai Namwa is a local species of banana grown in Thailand. Flour made from this banana was mixed with chitosan, a by product of the shrimp industry, for casting films as it has valuable characteristics including antimicrobial effects. Utilization of excess banana available in high season and chitosan can from the waste crustacean shells could help reduce waste while making available a value added product. Banana/chitosan films were produced using 0.5–2 g banana flour and 0.5 g chitosan in 100 ml aqueous solution. Film water vapor permeability, tensile properties, solubility and morphology were investigated. The composite yellowish film exhibited great water permeability of 38.81–41.66 g mm/m² day kPa. Tensile strength and elongation were in the range of 5.19–14.22 MPa and 1.64–2.59%, respectively while the solubility obtained was 40.90–64.21%. The presence of starch in the composite film makes possible water soluble and sealable bags or wraps, while the presence of chitosan gives them the antimicrobial property. The composite bags were found to protect asparagus, baby corn and Chinese cabbage against Staphylococcus aureus activity by serving as a good barrier and as a antimicrobial agent. With these properties the edible bag with its contents can be processed together during food preparation making its use very convenient.     

Fabrication and characterization of kidney bean (Phaseolus vulgaris L.) protein isolate–chitosan composite films at acidic pH

The kidney bean protein isolate-chitosan (KPI/CH) composite films were fabricated at acidic pH to design potential carriers for antimicrobials (e.g., nisin). Tensile and thermo-mechanical properties, surface hydrophobicity and surface free energy (γ) as well as microstructure of the composite films were evaluated. A peelable and self-supported film was obtained for the KPI alone, exhibiting the typical stiff behavior. In contrast, the complex between KPI and CH produced less rigid and much more flexible films, with decreased elastic modulus (EM), storage modulus (E′) and glass transition temperature (T_g). The inclusion of CH enhanced surface hydrophobicity of the films. Concomitantly, the surface free energy (γ) of the films exhibited a reduced tendency. Upon increasing CH-to-KPI ratios, the microstructures of the films changed gradually from protein continuous to bi-continuous, CH continuous pattern. Moreover, the KPI/CH blend films exhibited a visible compositional gradient, reflecting that the CH was rich in near-surface of the films, especially air side. Antimicrobial activity of the films was also analyzed, indicating the test bacteria, Bacillus subtilis, Escherichia coli and Salmonella were sensitive to KPI/CH composite films, in a CH-to-KPI dependent manner. The results presented here supported that the KPI/CH blend films are expected to serve as antimicrobial packaging for food or the carrier of antimicrobials (e.g., nisin).     

Effect of homogenization conditions on physicochemical properties of chitosan-based film-forming dispersions and films

Film-forming dispersions (FFD) based on high molecular weight chitosan (CH) alone or in combination with oleic acid (OA) were prepared under different homogenization conditions (rotor-stator or rotor stator together with microfluidization at different pressures). Film-forming dispersions (FFD) were characterized in terms of particle size distribution, rheological properties, distribution and ζ-potential. In order to study the impact of the properties of the FFD on the casted films, the water vapour permeability, mechanical properties and microstructure of the dry films were evaluated. Results showed that microfluidization promoted significant changes in the size and surface charge of the FFD particles, which in turn had an impact on the rheological properties of the FFD. The changes were more marked with the increase in microfluidization pressure. As regards film properties, the higher the microfluidization pressure in the FFD, the lower the water vapour permeability values and the stiffer the CH-OA composite films. These results were explained by film microstructure, which was observed by SEM.     

藻蓝蛋白-壳聚糖复合膜的制备及性能表征

以壳聚糖为基材,将藻蓝蛋白添加到壳聚糖膜中制成复合膜,探讨藻蓝蛋白添加配比对复合膜的理化性质、机械性能、及抑菌性的影响。结果表明:随着藻蓝蛋白添加比例增加(0.5%~1.0%,w/v),复合膜的水蒸气透过性与抗拉强度减小,而不透明度、抑菌活性及断裂伸长率增加。当藻蓝蛋白添加比例为1.0%时,复合膜表面、内部结构更均一致密,具有最大的不透明度(3.927 Abs₆₀₀·mm-1)、断裂伸长率(79.73%)和最低的水蒸气透过系数(1.273×10-10g·m-1·s-1·Pa-1)。1.0%复合膜对大肠杆菌的抑菌圈直径最大,为22.36 mm。该研究可为藻蓝蛋白-壳聚糖复合活性膜的应用提供理论依据。     

Antimicrobial activity of lauric arginate-coated polylactic acid films against Listeria monocytogenes and Salmonella typhimurium on cooked sliced ham

A novel type of environmentally friendly packaging with antibacterial activity was developed from lauric arginate (LAE)-coating of polylactic acid (PLA) films after surface activation using a corona discharge. Scanning electron microscopy (SEM)-based analysis of the LAE/PLA films confirmed the successful coating of LAE on the PLA surface. The mechanical properties of the LAE/PLA films with different levels of LAE-coating (0% to 2.6%[w/w]) were essentially the same as those of the neat PLA film. The antibacterial activity of the LAE/PLA films against Listeria monocytogenes and Salmonella enterica Serovar Typhimurium (S. Typhimurium) was confirmed by a qualitative modified agar diffusion assay and quantitative JIS Z 2801:2000 method. Using the LAE/PLA film as a food-contact antimicrobial packaging for cooked cured ham, as a model system, suggested a potential application to inhibit L. monocytogenes and S. Typhimurium on ham with a 0.07% (w/w) LAE coating on the PLA when high transparency is required, as evidenced from the 2 to 3 log CFU/tested film lower pathogen growth after 7 d storage but even greater antibacterial activity is obtained with a LAE coating level of 2.6% (w/w) but at the cost of a reduced transparency of the finished product. This article shows how we can simply develop functional green packaging of PLA for food with effective and efficient antimicrobial activity by use of LAE coating on the surface via corona discharge. PRACTICAL APPLICATION: The effectiveness of an innovative antimicrobial LAE-coated PLA film against foodborne pathogens was demonstrated. Importantly, the application of the LAE to form the LAE-coated PLA film can be customized within current film manufacturing lines.     

Antimicrobial effectiveness of bioactive packaging materials from edible chitosan and casein polymers: assessment on carrot, cheese, and salami

Antimicrobial packaging is one of the most promising active packaging systems for controlling spoilage and pathogenic microorganisms. In this work, the intrinsic antimicrobial properties of chitosan (CH) were combined with the excellent thermoplastic and film-forming properties of sodium caseinate (SC) to prepare SC/CH film-forming solutions and films. The antimicrobial effectiveness of SC, CH, and SC/CH coatings on the native microfloras of cheese, salami, and carrots was evaluated. In vitro assays through the test tube assay indicated that the most significant antimicrobial effect was achieved by CH and SC/CH solutions on carrot and cheese native microfloras. SC film-forming solutions did not exert antimicrobial activity on any of the native microflora studied. SC, CH, and SC/CH films stored in controlled environments showed that the retention of the antimicrobial action was observed until 5-d storage, at 65% relative humidity in both temperatures (10 °C and 20 °C). In vivo assays were also performed with SC, CH, and SC/CH applied as coatings or wrappers on the 3 food substrates. CH and SC/CH applied at both immersion and wrapper exerted a significant bactericidal action on mesophilic, psychrotrophic, and yeasts and molds counts, showing the 3 microbial populations analyzed a significant reduction (2.0 to 4.5 log CFU/g). An improvement of the bactericidal properties of the CH/SC blend respect to those of the neat CH film is reported. The ionic interaction between both macromolecules enhances its antimicrobial properties. Practical Application: The continuous consumer interest in high quality and food safety, combined with environmental concerns has stimulated the development and study of biodegradable coatings that avoid the use of synthetic materials. Among them, edible coatings, obtained from generally recognized as safe (GRAS) materials, have the potential to reduce weight loss, respiration rate, and improve food appearance and integrity. They can be used in combination with other food preservation techniques in order to extend the effectiveness of the food preservation chain. Moreover, antimicrobial films and coatings have innovated the concept of active packaging and have been developed to reduce, inhibit, or delay the growth of microorganisms on the surface of food in contact with the package. The use of antimicrobials packaging films to control the growth of microorganisms in food can have a significant impact on shelf-life extension and food safety. In addition, antimicrobial films can be prepared by the combination of inherent antimicrobial materials (that is, CH), with good film-forming protein-based ones (that is, SC). Therefore, the objective of this work is to study the performance of 2 biodegradable and edible biopolymers and their combination as natural packages for selected food products.     

Antimicrobial Activity of Chitosan Films Enriched with Essential Oils

ABSTRACT: Antimicrobial and physicochemical properties of chitosan films and chitosan films enriched with essential oils (EO) were determined in vitro and on processed meat. Antimicrobial effects of pure EO of anise, basil, coriander, and oregano, and of chitosan-essential oil films against Listeria monocytogenes and Escheri-chia coli O157:H7 were determined by an agar diffusion test. The antibacterial effects of the EO were similar when applied alone or incorporated in the films. The intensity of antimicrobial efficacy was in the following order: oregano > > coriander > basil > anise. The chitosan films and chitosan-oregano EO films were applied on inoculated bologna samples and stored 5 d at 10 °C. Pure chitosan films reduced L. monocytogenes by 2 logs, whereas the films with 1% and 2% oregano EO decreased the numbers of L. monocytogenes by 3.6 to 4 logs and E. coli by 3 logs. Pure chitosan films were 89 μm thick, whereas addition of 1% and 2% oregano EO increased thickness to 220 and 318 μm, respectively. During application on bologna discs, the films absorbed moisture, resulting in the final thickness of 143, 242, and 333 μm, respectively. Addition of oregano essential oil into the chitosan films decreased water vapor permeability, puncture and tensile strength, but increased elasticity of the films. The films have the potential to be used as active biodegradable films with strong antimicrobial effects.     

Composite and bi-layer films based on gelatin and chitosan

The aims of this work were: to develop composite, bi-layer and laminated biodegradable films based on gelatin and chitosan, to determine film barrier and mechanical properties and to characterize their microstructure.Gelatin and chitosan concentrations used were 7.5% and 1% (w/w), respectively. Glycerol (0.75%) was added as plasticizer.Physicochemical properties such as moisture content, transparency and color were analyzed. Composite and bi-layer systems showed a compact structure indicating a good compatibility between components.Water vapor permeability (WVP) was independent of film thickness up to 120 μm for gelatin films and 60 μm for chitosan ones. Both, bi-layer and laminated systems resulted effective alternatives to reduce WVP of composite films (at least 42.5%). Bi-layer systems showed better mechanical properties than laminated ones. The resistance at break increased from 54.3 for composite to 77.2 MPa for bi-layer films, whereas elongation at break values of both composite and bi-layer films were similar (2.2–5.7%).     

壳聚糖明胶可食用复合膜的制备与抗菌性能研究

以壳聚糖和明胶为复合膜骨架材料,通过加入0.3%(体积比)甘油增塑剂,制备具有显著抗菌性能的可食用复合膜。以较高的抗拉强度、较大的断裂伸长率、较低的水蒸气透过系数为主要性能指标,对成膜骨架材料壳聚糖和明胶的配比进行优化。研究结果表明,当壳聚糖浓度为1.5%、明胶浓度为1.25%时,以6∶4的体积比混合,制备获得机械性能良好(抗拉强度为13.24 MPa,断裂伸长率为112.45%),水蒸气透过系数较低(0.4032 mg·mm·kPa-1·h-1·m-2)的最优化复合膜。通过红外光谱、X射线衍射、扫描电镜等手段对复合膜进行表征。结果表明,与壳聚糖膜和明胶膜相比,复合膜的内部分子之间有较强的氢键和分子间作用力,膜内部致密且水蒸气不易通过,同时复合膜液对大肠杆菌、金黄色葡萄球菌和枯草芽孢杆菌均具有显著的抑制效果。