Antimicrobial Activity of Cinnamaldehyde and Eugenol and Their Activity after Incorporation into Cellulose‐based Packaging Films

Cinnamaldehyde and eugenol were investigated for their antimicrobial activity against 10 pathogenic and spoilage bacteria and three strains of yeast, using an agar‐well diffusion assay. The minimum inhibitory concentrations (MICs) of these compounds were determined using an agar dilution method. Finally, cinnamaldehyde‐incorporated and eugenol‐incorporated methyl cellulose films were prepared to obtain active antimicrobial packaging materials. These antimicrobial cellulose‐based packaging films were investigated for antimicrobial activity against target microorganisms using both an agar‐disc diffusion technique and a vapour diffusion technique. At a concentration of 50 µl/ml, cinnamaldehyde and eugenol revealed antimicrobial activity against all test strains. They showed zones of inhibition, ranging from 8.7 to 30.1 mm in diameter. Eugenol and cinnamaldehyde possessed ‘moderate?strong inhibitory’ and ‘strong?highly strong inhibitory’ characteristics, respectively. With MICs of 0.78?50 µl/ml, cinnamaldehyde and eugenol also inhibited the growth of all test microorganisms. Among the test microorganisms, Aeromonas hydrophila and Enterococcus faecalis were the most sensitive to cinnamaldehyde and eugenol. Cinnamaldehyde showed lower MICs against all test strains than those of eugenol. In an agar‐disc diffusion assay, cellulose‐based film containing cinnamaldehyde or eugenol totally failed to exhibit a clear inhibitory zone. However, it showed positive activity against all selected test strains in terms of size and enumeration of microbial colonies in a vapour diffusion assay. This study shows the potential use of cinnamaldehyde and eugenol for application in antimicrobial packaging film or coating. Copyright © 2011 John Wiley & Sons, Ltd.     

Development and evaluation of an edible antimicrobial film based on yam starch and chitosan

Edible antimicrobial films are an innovation within the biodegradable active packaging concept. They have been developed in order to reduce and/or inhibit the growth of microorganisms on the surface of foods. This study developed an edible antimicrobial film based on yam starch (Dioscorea alata) and chitosan and investigated its antimicrobial efficiency on Salmonella enteritidis. A solution of yam starch (4%) and glycerol (2%) was gelatinized in a viscoamilograph and chitosan added at concentrations of 1%, 3% and 5%. Films with and without chitosan were produced by the cast method. To evaluate the antimicrobial activity of the films, two suspensions of S. enteritidis were used in BHI medium, corresponding to counts of 2 × 10⁸ and 1.1 × 10⁶ CFU/ml. The suspensions (50 ml) were poured into flasks. The films were cut into 5 × 5 and 5 × 10 cm rectangles to be used at ratios of 1 : 1 (1 cm²/ml microorganism suspension) and 2 : 1 (2 cm²/ml). The film 30 µm thick on average. As a control, pure chitosan at an amount corresponding to that contained in the 3% and 5% films (5 × 10 cm) was added to flasks containing the microorganism suspension. Also, flasks containing only a suspension of S. enteritidis were used as control. The suspensions, in flasks, were kept at 37°C in a waterbath with agitation. Suspension aliquots were removed every hour for reading the optic density (OD₅₉₅) and plating onto PCA medium. The results showed that chitosan has a bactericidal effect upon S. enteritidis. Films treated with chitosan at different concentrations showed similar antimicrobial efficiency, in addition to being dependent on diffusion. The chitosan‐treated films caused a reduction of one to two log cycles in the number of microorganisms, whereas the pure chitosan presented a reduction of four to six log cycles compared with the control and starch film. The films showed good flexibility. Copyright © 2005 John Wiley & Sons, Ltd.     

Properties of antimicrobial plastics containing traditional food preservatives

Traditional food preservatives, sodium benzoate, sodium nitrite, potassium sorbate and sodium lactate, were incorporated into synthetic plastics, low‐density polyethylene (LDPE), poly(maleic acid‐co‐olefine), polystyrene (PS) and polyethylene terephthalate (PET), aimed at producing antimicrobial packaging material for foodstuffs. The study was undertaken on plaques (thickness 2 mm) and films (thickness 70–120 µm), whose antimicrobial test results clearly differed. Plaques containing 15% sodium nitrite inhibited both Aspergillus niger and Bacillus subtilis, whereas the same concentration of sodium benzoate and potassium sorbate had activity only against B. subtilis. Sodium lactate‐containing samples did not have any antimicrobial activity and none of the samples inhibited Escherichia coli. Antimicrobial substances added into PS and PET produced the strongest activities; however, due to the brittle structure of these materials, they were not tested further. Thus, more thorough tests for antimicrobial activity, migration and oxygen and water vapour permeability were carried out using LDPE films with 2.5–15% sodium benzoate and sodium nitrite. The effects of both substances on permeability properties were negligible. Although the total migration into food simulants measured from the films in many cases exceeded the limit value of 10 mg/dm², no antimicrobial activity was observed. Copyright © 2003 John Wiley & Sons, Ltd.     

Antimicrobial activity of glucose oxidase‐immobilized plasma‐activated polypropylene films

Antimicrobial enzyme, glucose oxidase (GOX), was covalently immobilized onto amino‐ and carboxyl‐plasma‐activated biorientated polypropylene films (BOPP) via glutaraldehyde and carbodiimide chemistries. N₂‐plasma + NH₃ and N₂‐plasma + CO₂ treatments were utilized to create amino (1.1 nmol/cm²) and carboxyl (0.9 nmol/cm²) groups densities onto the surface of BOPP films. GOX‐immobilized onto amino‐activated BOPP films using 2.5% glutaraldehyde produced higher enzymatic activities than GOX‐immobilized by 0.4% carbodiimide. Further immobilizations were carried out with glutaraldehyde as the coupling agent at temperatures of 4–75°C at pH 5.6 and 7.2. 10 s treatment was sufficient to immobilize GOX at high temperatures in both pH conditions, producing enzymatically active films which remained active over 30 days of storage. GOX covalently immobilized onto BOPP films completely inhibited the growth of Escherichia coli and substantially inhibited the growth of Bacillus subtilis; thus, they may have great potential to be exploited in various antimicrobial packaging film applications. Copyright © 2005 John Wiley & Sons, Ltd.     

Preservation of sliced ham through triclosan active film

Active packaging is an alternative to preserve perishable food. In this work, polyethylene antimicrobial active films containing different levels of triclosan (0, 2000 and 4000 mg kg^?1) were developed by extrusion. The films' efficacies were evaluated against Escherichia coli, Staphylococcus aureus, Listeria innocua, Salmonella choleraesuis and Pseudomonas aeruginosa growth using agar diffusion test and by monitoring the inhibition of E. coli and S. aureus inoculated on sliced cooked ham. The mechanical characteristics of the films were also evaluated with Universal Test Machine (Instron). The incorporation of triclosan did not affect the mechanical properties of antimicrobial films compared to the control film. The average film thickness was 82.0 µm and the tensile strength and elongation to break were 30.3 N and 46.2%, respectively. Films containing triclosan showed an antimicrobial effect in vitro against E. coli and S. aureus, with formation of an inhibition halo for both. However, this result was not observed for L. innocua, S. choleraesuis and P. aeruginosa, although, a decrease in colony density occurred around the film for both incubation temperatures (7 ± 2°C and 35 ± 2°C). Sliced ham packed with the antimicrobial films showed a reduction of 1.5 logarithmic cycles in comparison to ham in contact with a control film after 12 days of storage at 7 ± 2°C, for E. coli and S. aureus. Antimicrobial films present potential for application as active packaging materials, as they showed effective against some pathogenic microorganisms that can be transmitted by foods. Copyright © 2009 John Wiley & Sons, Ltd.     

Extruded Blends of Chitosan and Ethylene Copolymers for Antimicrobial Packaging

Chitosan was melt‐processed with an ethylene methyl acrylate copolymer ionomer and with an ethylene vinyl acetate copolymer to create antimicrobial extruded films. The key to obtaining a successful antimicrobial blend was the use of solid chitosonium acetate that remained after evaporation of water from the chitosan solution. When solid free‐flowing powders of chitosonium acetate were formed by spray drying chitosan solutions, blended in an extruder (at 2.5% and 4% chitosan) with Elvax® 3175 ethylene vinyl acetate copolymer, and extruded through a film die onto a chill roll to form films, the films exhibited antimicrobial activity against Escherichia coli 25922, Salmonella enterica serovar Enteritidis Nal^R, and Listeria monocytogenes Scott A. The log₁₀ reductions in CFU/ml after 24 h in a shake‐flask test were near 2 for films containing 4% chitosan. This melt‐blending/extrusion approach is expected to open applications for chitosan‐based antimicrobial packages and articles that were impossible or impractical with chitosan coatings. Copyright © 2011 John Wiley & Sons, Ltd.     

Antimicrobial Activity of Pomegranate (Punica granatum L.) Peel Extract,Physical, Mechanical,Barrier and Antimicrobial Properties of Pomegranate Peel Extract‐incorporated Sodium Caseinate Film and Application in Packaging for Ground Beef

In the present study, casein‐based edible films containing 1, 1.5 or 2 times of minimum inhibitory concentration of pomegranate peel extract (as antimicrobial agent) were prepared, and their physical, mechanical and antimicrobial impacts against two Gram‐positive and Gram‐negative bacterial strains were investigated. To evaluate the microstructure changes resulting from the addition of the antimicrobial extracts, scanning electron microscopy images were taken from both surface and cross section of the films. Different physical and mechanical properties of films were affected by the addition of pomegranate extract. For example, the water vapour permeability of films increased. Antimicrobial effectiveness of prepared films was more pronounced against Gram‐positive strain compared with Gram‐negative strain. Antimicrobial impact of edible films was also studied on ground meat. It was observed that antimicrobial activity of the films was mostly dependent on the types of microorganisms present in meat. Although they were not a suitable replacement for common films, they could substantially extend the shelf life of ground meat. Copyright © 2015 John Wiley & Sons, Ltd.     

Compensation of Pinhole Defects in Food Packages by Application of Iron‐based Oxygen Scavenging Multilayer Films

To protect sensitive food products from oxidative deterioration, multilayer barrier film systems and also modified atmosphere packaging are widely applied. However, the preservation of food quality in such packaging systems may be compromised by the presence of defects in the sealing layer of the films, especially when these are below a critical size, typically the detection limit of standard leak testers of 10 µm. The addition of an oxygen scavenger (OS) layer in barrier film structures could therefore provide extended protection against O₂ penetration through such defects. In this study, O₂ absorption of different multilayer film structures including an iron‐based OS were investigated under defined gas atmospheres. Measurement cells were thereby covered with plastic films of defined O₂ permeability to simulate conditions in a food package during storage with pinhole defect sizes of 10 and 17 µm. The results indicated that the OS film structures applied could only compensate for a defect size of 10 µm in the sealing layer. Analysis of the O₂ absorption of different multilayer film structures at 85% and 100% relative humidity showed that higher humidity accelerates the activation of the scavenger. After full activation, the scavenger kinetics are the same for 85% and 100% relative humidity. Long‐term storage experiments using the most effective film structure from the preliminary experiments were carried out to compare O₂ absorption of a snack food product in packages with and without an OS. The analyzed linear gradient of the reaction of the OS film and food product, respectively, indicated first‐order reaction kinetics with corresponding reaction constants calculated to be K (food product) 0.021 mg (O₂) mbar (O₂)^?1 day^?1 and K (OS film) 0.066 mg (O₂) mbar (O₂)^?1 day^?1. The reaction velocity of the OS was thus three times faster than that of the food. The applicability of OS multilayer film systems to compensate a critical pinhole defect size of 10 µm for sensitive food products could therefore be confirmed. The measurement of quality parameters for the status of lipid oxidation processes would help to verify this result. Copyright © 2012 John Wiley & Sons, Ltd.     

Sorption of uranium from underground leaching solutions with highly basic anion exchangers

Sorption of U on strongly basic anion exchangers AMP, AM-p, Lewatit K6267, Lewatit MonoPlus MP600XL, Purolite A500u, and Purolite A600u was studied at various temperatures in batch and dynamic experiments. The dynamic exchange capacities, (g U) dm^?3, of the anion exchangers to a breakthrough of 0.5 (mg U) dm^?3 at 6–8°C were determined: AMP (9.56) > Purolite A600u (9.26) > Lewatit K6267 (9.13) > Purolite A500u, Lewatit MonoPlus MP600XL (8.87) > AM-p (5.88). Also, the total dynamic exchange capacities, (g U) dm^?3, of the anion exchangers at 6–8°C were determined: AMP (37.13) > Purolite A500u (31.79) > Lewatit MonoPlus MP600XL (28.88) > Lewatit K6267 (27.74) > AM-p (27.58) > Purolite A600u (25.24). The concentration equilibrium distribution coefficients (K _d) of U on these resins were determined in batch experiments. The highest value of K _d = 2869 at 6°C and initial uranium concentration in solution of 65 mg dm^?3 was attained with AMP of commercial grain-size distribution. At 24°C and the same uranium concentration, the highest value of K _d = 5195 was obtained with separated 0.8–1.0-mm fraction of AMP. The kinetic experiments were performed, and the internal diffusion step was found to be the limiting step of the U sorption with all the resins under consideration. The internal diffusion coefficients in ion exchanger grains were calculated to compare the resins with each other.     

The Effect of Coating Process and Additives on EVA Coated Tyvek® for Gas Sterilizable Medical Packaging Applications

Tyvek^®, as an ethylene oxide (EtO) gas sterile medical packaging material with a high‐gas permeation and serving as an excellent microbial barrier, must be coated with heat‐sealable adhesives to thermally seal various plastic packaging trays or films. Tyvek^® sheet coated with heat‐sealable adhesives must have both porous structure and good sealing strength to various substrates. In this study, an acid pre‐coating method was distinctively introduced to minimize reactions between the blowing agent and acid during mixing, to resultantly generate ethyl vinyl acetate (EVA) layers with porous structure on Tyvek^® sheets. To determine the feasibility of applying the as‐prepared coated Tyvek^® as a sterile medical packaging material, we investigated the properties of the coating solution and coated Tyvek^® as a function of process and additive composition. Finally, EtO gas sterilization tests were performed, and property changes in the coated Tyvek^® were investigated. Properties of the coated Tyvek^® were strongly dependent on the pre‐coating process and the composition of various additives. Pre‐coating with citric acid led to less of a reaction between citric acid and ammonium carbonate as a blowing agent during mixing and resulted in both good seal strength and air permeation for the coated Tyvek^® sheets. The coated Tyvek^® sheets, composed of a water‐based EVA emulsion solution with various additives, were not affected by the EtO sterilization process and yielded good resistance to humidity, EtO gas and vacuum cycles. The coated Tyvek^® sheets prepared by applying an acid pre‐coating may be a promising candidate for gas sterilizable medical device packaging materials. Copyright © 2017 John Wiley & Sons, Ltd.     

The Effect of Active Packaging on Minimizing Food Losses: Life Cycle Assessment (LCA) of Essential Oil Component‐enabled Packaging for Fresh Beef

Packaging plays an important role in ensuring food safety and quality, and the development of active packaging, especially antimicrobial packaging, enables actively inhibiting/killing the microorganisms causing food spoilage and thus extending the product's shelf life. A survey of the publications revealed that generally 50% shelf life extension is possible. The goal of this study is to assess the overall environmental performance of the food and packaging system considering the effect of food loss reduction by using active packaging. A comparative life cycle assessment has been carried out, focusing on a case study: essential oil component‐enabled packaging for fresh beef. Different scenarios were set up to contrast the situations of food using conventional packaging (current situation) and food using novel active packaging (containing active coating). Additionally, a sensitivity analysis has been integrated, aiming to identify the breakeven point of the balance. In the scenarios using the best‐performance active packaging, it was shown that a breakeven point can be achieved across the four impact categories evaluated, including global warming, fossil energy demand, acidification potential and eutrophication potential. It is expected that the obtained results would serve as guidelines for active packaging development striving for a positive eco‐profile of the food and packaging system. Copyright © 2015 John Wiley & Sons, Ltd.     

抗菌食品包装纸的研究现状及发展趋势

目的对国内外食品抗菌包装纸的研究现状进行综述分析,总结食品抗菌包装纸的技术发展趋势,以期为抗菌纸的研究提供有效参考。方法对抗菌食品包装纸的抗菌剂——无机型抗菌剂、化学合成型抗菌剂、天然抗菌剂及其主要抗菌机理进行阐述;根据涂布、添加浆料、浸渍/喷淋、纤维改性等加工方法对抗菌食品包装纸进行分类;分析和总结国内外食品抗菌包装纸的最新研究成果;从高效安全抗菌剂及应用剂型的研发,抗菌纸抗菌效果的持久性和作用方式的提升,食品抗菌包装纸的产业化工艺技术的开发等方面指出今后食品抗菌包装纸的发展趋势。结果食品抗菌包装纸的开发仍处于初步阶段,抗菌纸的产业化推广不够,抗菌纸中抗菌剂的安全性、稳定性、可持久性还有待进一步改善。结论随着对绿色安全高效抗菌剂、应用剂型和抗菌纸加工技术的进一步研究,食品抗菌包装纸必将得到更广泛的推广应用。     

The effectiveness of hexamethylenetetramine‐incorporated plastic for the active packaging of foods

The feasibility of LDPE films containing 0.2 or 0.5% (w/w) hexamethylenetetramine (HMT) as antimicrobial packaging material to inhibit microbial growth on the surface of foods was investigated. As HMT is allowed in Europe to be used as a preservative under certain conditions, and as it is mentioned on the list of additives notified to the European Commission as substances which may be used in plastics intended in contact with food products, this compound offers good opportunities for the manufacturing of an antimicrobial packaging material. In a first experiment, fresh orange juice was vacuum packaged in LDPE films containing 0, 0.2 and 0.5% (w/w) HMT and stored at 6°C for 39 days. Every day and later every 3 days, packages of orange juice were analysed for yeasts and lactic acid bacteria. The shelf‐life of orange juice, could not be prolonged significantly by packaging into a 0.2% or 0.5% (w/w) HMT‐containing film. In a second experiment, however, packaging of cooked ham in a 0.5% (w/w) containing LDPE film, significantly affected shelf‐life. After 20 days a significant reduction of total aerobic count and lactic acid bacteria was observed. In an additional migration test, it became clear that the level of HMT released into orange juice was close to the specific migration limit of 15 mg CH₂O/kg imposed by the EC. Copyright © 2000 John Wiley & Sons, Ltd.     

The Binary Effect on Methicillin‐Resistant Staphylococcus aureus of Polymeric Nanovesicles Appended by Proline‐Rich Amino Acid Sequences and Inorganic Nanoparticles

Prevalent research underscores efforts to engineer highly sophisticated nanovesicles that are functionalized to combat antibiotic‐resistant bacterial infections, especially those caused by methicillin‐resistant Staphylococcus aureus (MRSA), and that aid with wound healing or immunomodulation. This is especially relevant for patients who are susceptible to Staphylococcus aureus infections postoperatively. Here, antibacterial formulations are incorporated into polymeric, biocompatible vesicles called polymersomes (PsNPs) that self‐assemble via hydrophobic interactions of admixed aqueous and organic substances. Nano‐PsNPs are synthesized using a high molecular weight amphiphilic block copolymer, and are conjugated to include antimicrobial peptides (AMPs) along the peripheral hydrophilic region and silver nanoparticles (AgNPs) inside their hydrophobic corona. In vitro testing on bacterial and human cell lines indicates that finely tuned treatment concentrations of AMP and AgNPs in PsNPs synergistically inhibits the growth of MRSA without posing significant side effects, as compared with other potent treatment strategies. A ratio of silver‐to‐AMP of about 1:5.8 corresponding to ≈11.6 µg mL^?1 of silver nanoparticles and 14.3 × 10^?6 m of the peptide, yields complete MRSA inhibition over a 23 h time frame. This bacteriostatic activity, coupled with nominal cytotoxicity toward native human dermal fibroblast cells, extends the potential for AMP/AgNP polymersome therapies to replace antibiotics in the clinical setting.     

Wide‐spectrum antimicrobial packaging materials incorporating nisin and chitosan in the coating

Nisin and/or chitosan were coated, in 3% concentrations, onto paper with a binder medium of vinyl acetate–ethylene co‐polymer to provide antimicrobial activity for use in food packaging. The combined use of nisin and chitosan in the coating was an attempt to give a wide antimicrobial spectrum that could inhibit the growth of several food spoilage and poisonous microorganisms. The migration of the preservative from the coatings to water was evaluated at 10°C and related to the suppressed microbial growth in the water and microbial medium. After 8 days, 8.1–8.3% of nisin and 1.0–1.2% of chitosan had migrated, and the migration of each was not affected by the presence of the other. The paper coated with nisin was more effective than the chitosan‐coated paper in inhibiting the Gram‐positive bacterium, Listeria monocytogenes, whereas the latter was more effective against Escherichia coli O157:H7. Combined inclusion of nisin and chitosan in the coating gave antimicrobial activity against both bacterial strains, and could improve the microbial stability of milk and orange juice stored at 10°C. Copyright © 2003 John Wiley & Sons, Ltd.     

食品抗菌包装及其在鲜肉包装中的应用

重点对食品抗菌包装的5 种类型(在包装中添加含有挥发性抗菌成分的小袋或衬垫;直接合并抗菌剂到聚合物包装材料中;在聚合物表面涂布或吸附抗菌剂;通过离子键或共价键将抗菌剂固定到聚合物中;使用本身具有抗菌作用的包装材料)及其各自的特点进行了综述,最后介绍了抗菌包装在易腐食品鲜肉中的具体应用及实际抗菌保鲜效果,并对抗菌食品包装的发展趋势进行了展望。     

Development and evaluation of active packaging for sliced mozzarella preservation

Antimicrobial films were formed by the incorporation of nisin (NI), natamycin (NA) and a combination of both (NI + NA) into cellulose polymer. Film efficacies were evaluated in vitro against Staphylococcus aureus ATCC 6538, Listeria monocytogenes ATCC 15313, Penicillium sp. and Geotrichum sp. The films were also evaluated on sliced mozzarella cheese against moulds and yeasts, Staphylococcus sp. and psychrotrophic bacteria. Mechanical and microscopic properties of the films and the diffusion of the antimicrobial agents from the film to the cheese were also evaluated. Films containing NI showed an antimicrobial effect in vitro against S. aureus and L. monocytogenes, while films containing NA were effective in vitro against Penicillium sp. and Geotrichum sp. By the ninth day of storage at 12 ± 2°C, the count of yeasts and moulds on cheese covered with films containing NA decreased 2 log10 units compared with the count on cheese with control films. NI film did not show an effect against Staphylococcus sp., but it was effective against psychrotrophic bacteria for 6 days of storage of the cheese. The incorporation of antimicrobial compounds decreased the resistance and elongation of the films and caused changes in their molecular conformation. NI diffusion from the films to the cheese was not detected; however, time‐dependent diffusion of NA from the film containing NI + NA was measured. The incorporation of NI and NA together in the films did not show an effect. The film containing NA showed potential for application as active food packaging for sliced mozzarella cheese. Copyright © 2008 John Wiley & Sons, Ltd.     

2D Chalcogenide Nanoplate Assemblies for Thermoelectric Applications

Engineered atomic dislocations have been used to create a novel, Sb₂Te₃ nanoplate‐like architecture that exhibits a unique antisymmetric chirality. High‐resolution transmission electron microscopy (HRTEM) coupled with atomic force microscopy and X‐ray photoelectron spectroscopy reveals the architectures to be extremely well ordered with little residual strain. Surface modification of these topologically complex macrostructures (≈3 µm) has been achieved by direct growth of metallic Ag nanoparticles onto the edge sites of the Sb₂Te₃. Again, HRTEM shows this nanoparticle decoration to be atomically sharp at the boundaries and regularly spaced along the selvedge of the nanostructure. Transport experiments of densified films of these assemblies exhibit marked increases in carrier density after nanoengineering, yielding 3.5 × 10⁴ S m^?1 in electrical conductivity. An increased Seebeck coefficient by 20% in parallel with electrical conductivity is also observed. This gives a thermoelectric power factor of 371 µW m^?1 K^?2, which is the highest value for a flexible, freestanding film to date. These results suggest an entirely new direction in the search for wearable power harvesters based on topologically complex, low‐dimensional nanoassemblies.     

Properties of polysaccharide‐coated polypropylene films as affected by biopolymer and plasticizer types

Plasticized polysaccharide coatings on polypropylene (PP) film were prepared to evaluate the optical and tensile properties of the resulting coated films, as affected by biopolymer and plasticizer types, in order to develop a novel film structure of biopolymer coatings on common plastics intended for food packaging applications. Composite structures of PP film coated with several kinds of polysaccharides (MC, HPMC, chitosan, κ ‐carrageenan, dextrin) and plasticizers (PG, glycerol, PEG, sucrose, sorbitol) were obtained through a simple casting method. High glossy surfaces were observed on the coated films with chitosan and κ ‐carrageenan, with the sucrose‐plasticized chitosan coating giving the highest gloss of 142.7 GU. Biopolymers, but no plasticizers, exerted noticeable influence on the colour of the coated films. Chitosan‐ and κ ‐carrageenan‐coated PP films also showed greater transparency, tensile strength and elongation than the other coated films. Nisin‐incorporated κ ‐carrageenan coatings on PP film exhibited significant bacterial growth inhibition against Lactobacillus plantarum . The results suggest that coatings based on chitosan and κ ‐carrageenan with proper plasticizers possess excellent visual and mechanical characteristics and have great potential for acting efficiently as antimicrobial agent carriers in active packaging systems. Copyright © 2004 John Wiley & Sons, Ltd.     

Tyrosinase‐catalysed grafting of food‐grade gallates to chitosan: surface properties of novel functional coatings

Plasma‐activated biaxially oriented polypropylene (BOPP) films and paper substrate have been coated with functional chitosan solutions. Plasma treatment increased the amount of surface peroxide groups and carboxyl groups on the BOPP films. As a result of plasma activation, the surface energy increased from 30 to 50 dynes/cm. The enzyme tyrosinase catalysed the grafting of octyl gallate and dodecyl gallate to amino groups of chitosan polysaccharide. Resulting coatings exhibited strong antimicrobial activity against Gram‐positive Staphylococcus aureus and Gram‐negative Listeria innocua. After 24 h of incubation, a total reduction in both bacteria cell numbers varied between >4.9 and 1.4 logarithmic units. Grafted dodecyl gallate and octyl gallate at pH 6 were found to have the lowest reduction values of <3 logarithmic units for S. aureus, while 1.4 logarithmic reduction value was obtained for grafted dodecyl gallate at pH 6 against L. innocua. Chitosan coatings were also effective barrier layers against oxygen transmission although the transmission rates clearly increased in high‐humidity conditions. In dry conditions, however, the transmission rate of 2 cm³/(m² · 24 h) was obtained with chitosan‐coated BOPP. Coatings did not have any effects on water vapour transmission. Both gallates were successfully grafted at pH 6. As increased flocculation and colour formation indicated, the tyrosinase‐catalysed grafting was more powerful with octyl gallate. Dodecyl gallate containing chitosan coatings was more hydrophobic as compared to octyl gallate. Total migration of substances into 95% ethanol was ≥5 mg/dm², thus materials may be exploitable in packaging purposes in direct contact with certain foodstuffs. Copyright © 2008 John Wiley & Sons, Ltd.