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.     

Characterization of antimicrobial films containing basil extracts

The properties of low‐density polyethylene (LDPE)‐based films containing either linalool or methylchavicol as antimicrobial (AM) additives were evaluated. Slight decreases in transparency, water vapour and oxygen transmission rates were found in the extruded films containing 0.34% w/w linalool or methylchavicol. The infrared (IR) spectra of the AM films were similar to that of additive‐free LDPE film. However, carbonyl peaks could also be observed in the spectra of the AM films. There was no significant difference in the degree of crystallinity and the melting temperature range of the different films. Derivative thermogravimetry mass‐loss curves showed that the thermal decomposition temperatures of the AM films were marginally lower than that of LDPE film. Electron micrographs indicated that AM LDPE‐based films exhibited no evidence of changes in microstructure to suggest that linalool and methylchavicol were not evenly distributed in the film. Copyright © 2006 John Wiley & Sons, Ltd.     

Low density polyethylene – Chitosan composites

With the aim of develop new materials for active food packaging, composites of low-density polyethylene (LDPE) with chitosan (CS) or chitosan sodium montmorillonite clay nanocomposites (CSnano), with or without Irganox 1076 commercial synthetic antioxidant or vitamin E (VE) as natural antioxidant were prepared by melt processing. The obtained materials have been characterized by processing behavior, mechanical and thermal properties, positive groups determination, atomic force microscopy and standard tests to assess antimicrobial and antioxidant activities. The compositions assuring insignificant decrease in mechanical and thermal properties were selected as LDPE/3CSnano/VE and LDPE/6CSnano/VE. It has been shown the chitosan imparts antimicrobial properties to LDPE films while the vitamin E increased the oxidation induction period, especially for materials containing chitosan nanocomposites. The incorporation of both chitosan nanocomposites and vitamin E in polyethylene gave films with good antimicrobial and thermal properties because of significant increase of charge surface and important changes in surface topology and antimicrobial activity because of a synergistic effect. The nanocomposites cannot only passively protect the food against environmental factors, but they may enhance shelf life of food products.     

Development of multilayer films with improved aroma barrier properties for durian packaging application

The symmetrical A/B/A structure of multilayer blown films was fabricated in this study. The immiscible low‐density polyethylene/polylactic acid (LDPE/PLA) blend was set as a core (B) layer and LDPE was used as skin (A) layers. The compositions of PLA in the core layer were varied from 20 to 50 wt%. The thickness of each layer was 10 μm (total film thickness of ~ 30 μm). In a blown film co‐extrusion process, the morphology of the fiber/ribbon‐like structures of LDPE/PLA blend was developed. Such structures had interesting effects on gas permeability and aroma barrier properties of the films. For instance, multilayer LDPE films containing 40 and 50 wt% PLA (P40 and P50) showed the reduction of oxygen permeability (PO₂) approximately 20% and 43%, respectively, compared with the neat LDPE film. A long tortuous path for gas and aroma transportation through film thickness was created from the developed ribbon‐like structures of the PLA minor phase. For durian packaging application, fresh‐cut durian of 300 g was packed in the developed multilayer films, LDPE, and HDPE (Control), stored at 4°C for 7 days. Results demonstrated that the steady‐state condition of 10% to 13% O₂ and 8% to 10% CO₂ was achieved in all packages except in the HDPE. Moreover, the P40 and P50 films exhibited an outstanding aroma barrier property for three major durian volatiles : diethyl sulfide, ethyl propanoate, and 2‐ethyl‐1‐hexanol. Overall results clearly indicated that the multilayer LDPE films containing PLA exhibited a significantly improved aroma barrier performance with optimum gas permeability desirable for modified atmosphere packaging to retain quality of fresh‐cut durian throughout the storage period.     

Microperforation of Three Common Plastic Films by Laser and Their Enhanced Oxygen Transmission for Fresh Produce Packaging

Three different plastic films of biaxially oriented polypropylene (BOPP), biaxially oriented polyethylene terephthalate (BOPET) and low‐density polyethylene (LDPE) were perforated using Nd‐YAG laser. Effects of laser pulse energy were examined by varying energies from 50 to 250 mJ where the pulse duration and pulse repetition were kept constant at 10 ns and 1 Hz, respectively. It was found that perforation diameters of all films increased with increasing pulse energies. Observed perforations were different among the three film types. Explanation was contributed to material inherent property and its interaction with laser. Incorporation of an inorganic filler (i.e. silica based anti‐blocking agent used in packaging film) of 0.5 wt% into the LDPE films (0.5Si‐LDPE) could improve perforation performance for LDPE. This was attributed to an increased thermal diffusivity of the 0.5Si‐LDPE film. Commercial BOPET and BOPP films containing 97 microholes/m² (hole diameter of ~100 µm) showed an improvement in oxygen transmission rates (OTR) of 18 and 5 times that of the neat films without perforation. In the case of perforated 0.5Si‐LDPE films having similar perforations of 97 microholes/m² and perforation diameter of 100 µm, a two‐fold increase of OTR was obtained. Gas transmission rates of the microperforated films were measured based on the static method. Measured OTR and CO₂TR values of the three films with varying perforation diameters in a range of ~40–300 µm were compared and discussed. Overall results clearly indicate that perforation by laser is an effective process in developing breathable films with tailored oxygen transmission property for fresh produce packaging. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of Polyethylene Packaging Modified with Silver Particles on the Microbial,Sensory and Appearance of Dried Barberry

Low‐density polyethylene (LDPE) packages containing submicrometre‐sized silver particles (Ag‐LDPE) were produced by extrusion method and used as packaging material for barberry packaging. The effects of Ag‐LDPE packages on the microbial factors, apparent color and sensory factors of dried barberry were investigated in comparison with the pure polystyrene packages. Ag‐LDPE packages showed antimicrobial effects on barberry compared with pure polystyrene packages. In comparison with pure polystyrene packages, Ag‐LDPE film with 2 weight percent (wt%) of silver particles revealed antimicrobial activity against mold and total bacteria count of approximately 2.3 and 2.84 log₁₀ reductions in colony‐forming units, respectively. Ag‐LDPE packages in concentration of more than 1 wt% of silver particles preserved the appearance quality of the barberry better than pure polystyrene packages. The barberries packaged in Ag‐LDPE film with 1 wt% of silver particles retained their red color and brightness for approximately 2 to 3 weeks more than barberries packaged in pure polystyrene films. Ag‐LDPE packages assisted in the improvement of aroma, taste and total acceptance of barberry in comparison with pure polystyrene packages except in the low concentration of silver particles of approximately 0.02 wt%. The taste, aroma, appearance and also total acceptance of barberries packaged in Ag‐LDPE film with 1 wt% silver particles were preserved for approximately 2 to 3, 1 to 4, 2 to 5 and 2 to 4 weeks, respectively, more than barberries packaged in pure polystyrene films. Copyright © 2012 John Wiley & Sons, Ltd.     

Low‐density Polyethylene Films Loaded by Titanium Dioxide and Zinc Oxide Nanoparticles as a New Active Packaging System against Escherichia coli O157:H7 in Fresh Calf Minced Meat

Antibacterial packaging is introduced as a new method to prevent microbial food spoilage. Antibacterial effects of TiO₂, ZnO and mixed TiO₂–ZnO nanoparticle‐coated low‐density polyethylene (LDPE) films on Escherichia coli PTCC1330 were investigated. Bactericidal efficiency of 0.5%, 1% and 2% TiO₂ and ZnO nanoparticles and also 1% mixed TiO₂–ZnO nanoparticles with ratios of 25/75, 50/50 and 75/25 were tested under ultraviolet (UV) and fluorescent lights at two states: films alone and fresh calf minced meat packed. Maximum colony‐forming unit (CFU) reduction of 99.8% and 99.7% were obtained using 1% and 2% ZnO nanoparticle‐coated LDPE film under fluorescent light for films alone as well as 99.8% and 99.6% for fresh calf minced meat packed. 90.3% and 51.8% CFU reduction were recorded for 1% TiO₂ nanoparticle‐coated LDPE films in the presence of UV light at direct contact with bacteria and fresh calf minced meat packed, respectively. Maximum CFU reductions of 96% and 64.1% were obtained using 50/50 ratio of TiO₂/ZnO nanoparticles at the presence of UV light for film alone and fresh calf minced meat packed, respectively. ZnO nanoparticle‐coated LDPE films were identified as the best case to improve shelf life and prevent E. coli growth in fresh calf minced meat.     

Development of an Active Thermoplastic Film with Oxygen Scavengers Made of Activated Carbon and Sodium Erythorbate

An active thermoplastic film made of low‐density polyethylene (LDPE) filled with oxygen scavengers made of powdered activated carbon (PAC) impregnated with sodium erythorbate (SE) was developed for packaging applications. Initial tests indicated that the impregnation of PAC with SE enhanced the heat resistance of SE, thereby allowing processing at temperatures typical of LDPE manufacturing. Subsequently, LDPE films with PAC/SE particles were manufactured in coupons that represented a typical juice package, and experiments indicated that these films absorbed 3.57 mg of oxygen in 11 days. This amount corresponded to 80% the concentration of oxygen in the headspace of the package. Furthermore, findings indicated that active particles alone have 10 times higher oxygen absorption capacity than the active LDPE film. Finally, the physical properties of the film were characterized by microscopy where oxygen scavengers showed a good dispersion within the matrix. However, 20 wt.% of these active particles decreased tensile strength of the film by 53%. Copyright © 2014 John Wiley & Sons, Ltd.     

透明阻光薄膜对固体饮料变色的影响

制备了稀土铕转光剂添加量分别为0.2%,0.5%,1.3%和2.0%(质量分数)的LDPE转光膜,测定了其在200～800 nm区间内的透射光谱。将LDPE转光膜用于橙味固体饮料的包装,并置于UV灯下进行照射,观察了其颜色变化。以橙味固体饮料的吸光度值作为变色指标,得到了吸光度值与UV灯光照时间的变化关系。结果表明,稀土铕转光剂添加量为1.3%的透明LDPE转光膜可作为该产品的包装材料,可使其颜色保持的时间最长。     

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.     

Evaluation of Antifungal Activity of Antimicrobial Agents on Cheddar Cheese

The antifungal activity against Aspergillus niger of the antimicrobial (AM) agents linalool, carvacrol and thymol incorporated in the coatings of starch‐based films was investigated. The activity was initially determined on a solid medium using the modified microatmosphere method and then examined on Cheddar cheese. On the solid media, all the AM films demonstrated a significant inhibitory effect against A. niger growth. The inhibitory effect of the AM films containing 2.38% (w/w) AM agents is reflected by the colony diameters that were 29.3, 25.4 and 21.3 mm for linalool, carvacrol and thymol, respectively, at 25°C after 7 days incubation compared with the control sample where the colony diameter was 85.3 mm. The AM films containing 2.38% (w/w) linalool, carvacrol or thymol reduced the population of A. niger on the surface of Cheddar cheese by 1.8, 2.0 and 2.2 log CFU/g, respectively, after 35 days of storage at 15°C. The results suggest that starch‐based film coated with an AM agent has the potential for being used as a fungicidal packaging system. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of hinokitiol impregnated sheets on shelf life and quality of “KEK‐1” tomatoes during storage

Hinokitiol (β‐thujaplicin, volatile oil extracted from the wood of Hiba arborvitae [Thujopsis dolabrata var. hondae], cypress family) is a natural preservative, antimicrobial, and chelating agent, used to prevent decay and extend the shelf life of fruits and vegetables. In the present study, we used nonwoven rayon sheets impregnated with hinokitiol to conduct packaging studies. Mature green tomatoes var. “KEK‐1” were packaged under three packaging conditions, ie, modified atmosphere packaging (MAP), MAP + hinokitiol (MH), and perforated film package (as control), and their quality attributes were compared during storage. The packaging materials used were low‐density polyethylene (LDPE) film (40 μm) and fresh sheets of nonwoven rayon impregnated with hinokitiol. O₂ in the MAP packaged tomatoes were retained throughout the storage period (3% to 5% O₂). Results showed that MH had slightly improved quality attributes throughout the storage period when compared with MAP alone. Expression levels of LeACS, LeADH, and LeTBG4 genes were higher in 5 and 9 days of control when compared with MAP and MH. “KEK‐1” tomatoes had longer shelf life under MAP and MH packaging and maintained the quality at 15°C. Hence, the effect of the MAP with bioactive packaging treatments could be effective in the future application for the extension of shelf life and quality of fruits and vegetables.     

Evaluation of the Effectiveness of a New Antimicrobial Active Packaging for Fresh Atlantic Salmon (Salmo Salar L.) Shelf Life

Nowadays, consumers demand for fresh, high‐quality seafood products continues to climb, especially in affluent, developed nations. At the same time, there is increasing attention regarding improved utilization of seafood for human consumption; Atlantic salmon is the main species in Chile aquaculture, and most of the salmon are exported as fresh fish to USA. It is well documented that low storage temperature inhibit bacterial growth and biochemical degradation, thus facilitating prolonged shelf life. Partly freezing the outer fillet layer from ?0.5°C to ?2.0°C (superchilling) has proven to be more efficient in inhibiting biochemical changes and bacterial spoilage compared with traditional chilling. Nevertheless, antimicrobial active packaging offers the possibility to increase product shelf life through the reduction of the microbiological damage of the product during its transportation, and thus increasing consumer safety and health. The main objective of this study was to compare the effects of an active antimicrobial packaging on microbiological growth, sensory attributes and instrumental quality measurements of raw Atlantic salmon (Salmo salar) fillets. Flexible plastic films containing Thymol as antimicrobial agent were used for salmon packaging. Salmon were stored at 2°C, 4°C and 8°C. Analyses of aerobic mesophilic bacteria and psicrophilic bacteria count were carried out at 1, 3, 8, 11, 15 and 18 days. L*a*b* colour evolution, overall sensorial properties and chemical evolution were studied. Application of active antimicrobial packaging for fillet salmon reduced the microbial count for least 18 days at 2°C. No modification of the sensorial properties was detected by the sensorial panel, indicating that the antimicrobial compound used in the present study, thymol, is compatible with salmon packaging. Copyright © 2011 John Wiley & Sons, Ltd.     

碳钢用新型气相防锈包装膜的制备与性能研究

目的 以正癸酸（CA）为缓蚀剂制备一种新型气相防锈包装膜,以期拓展中长链脂肪酸类缓蚀剂在防锈包装中的应用。方法 利用挤出吹塑法制备了含不同质量分数（0、0.5%、1.0%、2.0%）CA的低密度聚乙烯（LDPE）基气相防锈包装膜,试验测定分析CA添加量对包装膜光学、力学、阻隔、缓蚀等性能的影响。结果 CA的添加可改善LDPE包装膜的韧性,其质量分数为0.5%、1.0%、2.0%时,可使包装膜的水蒸气阻隔性能分别提高3.7%、17.9%、14.8%;CA质量分数为1.0%和2.0%的包装膜可使低碳钢在交变湿热环境下保持9周期无锈蚀,满足国标对气相防锈包装膜的相关性能要求。结论 添加CA的气相防锈包装膜可有效延缓碳钢腐蚀,为该类新型气相防锈包装膜研制提供技术支撑。     

A study of the absorption of fruit juice volatiles by the sealant layer in flexible packaging containers (the effect of package on quality of fruit juice,part IV)

Various experimental packaging containers were tested for their tendency to absorb fruit juice volatiles in the innermost heat-sealing layer. Analysis of head-space gas by GLC and sensory evaluations were carried out in order to evaluate the effect of each type of sealant. Coextrusion sealants (thin low-density polyethylene, LDPE), a sealant containing the orange essence powdered with cyclo-dextrin (CD), and polyethylene-terephthalate (PET) or polyacrylonitrile (PAN), synthetic resisns with high transition temperatures (T_g) were prepared. Coextrusion or CD-containing sealants as compared with LDPE, reduced the sorption of d-Limonene from Mandarin orange [Citrum unshiu Marc.] juice by 15–20% but did not show effective results in sensory evaluations. On the other hand PET or PAN sealants showed no sorption at all. Similar results were obtained with 'citrus mix' model essence. However, LDPE also did not show volatile sorption in the case of 'soft fruit mix' model essence. It is difficult to prevent sorption of the volatiles of citrus fruit juices if the sealants are of the coextrusion type or CD-containing LDPE type. Sorption can be controlled most effectively when the sealats are PET or PAN.     

Use of antimicrobial methylcellulose films to control Staphylococcus aureus during storage of Kasar cheese

Olive leaf extract (OLE) (Olea europaea L.) is a natural product that has antimicrobial effect on many food pathogens. In this study, methylcellulose (MC) based antimicrobial films containing 0.5–3% (w/v) OLE and glycerol (1.6%, v/v) were produced. The effects of OLE amount on the water vapour permeability (WVP), mechanical and antimicrobial properties of the films were investigated. The films were effective against Staphylococcus aureus (ATCC 25923). The OLE in the film solution caused a decrease in WVP and elongation (E), and an increase in tensile strength (TS). The MC films containing 1.5% (w/v) OLE were applied on Kasar cheese slices inoculated with S. aureus. The count of S. aureus decreased 0.68 and 1.22 log cycle at the 7th and 14th days, respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

超市蔬菜用阻光包装膜的研究

为了减小超市灯光中紫外线对包装鲜切西兰花的货架寿命的影响,采用LDPE与紫外线吸收剂UV-531共混的方法制备选择性阻光薄膜,UV-531所占质量分数分别为0,0.1%,0.3%和0.5%。使用制备的4种薄膜和超市现用LLDPE保鲜膜包装鲜切西兰花,置于超市用灯光下进行保鲜研究。结果表明:添加紫外线吸收剂的LDPE薄膜的透光率随着紫外线吸收剂添加量的增加而降低;在室温(29+1)℃条件下,添加紫外线吸收剂的LDPE薄膜对鲜切西兰花的保鲜效果均好于超市现用LLDPE保鲜膜;其中添加量为0.3%时能够更好地保护鲜切西兰花的叶绿素和水分,保鲜效果最好。     

转光薄膜对绿颜色蔬菜品质影响的研究

目的延长绿颜色蔬菜的货架寿命,保护绿色蔬菜品质。方法模拟某超市果蔬区的销售环境,以鲜切西兰花为例,选择单基双能转光剂(RBI),吹制添加质量分数为0.5%,0.8%,1.2%,1.5%,2.0%的低密度聚乙烯(LDPE)薄膜。对转光薄膜的气体透过性和光学性能进行测试,分别将添加不同含量单基双能转光剂的LDPE薄膜包装鲜切西兰花,并置于模拟超市的光照环境下,测定试验样品的质量、维生素C含量、叶绿素含量等变化,并对试验样品进行感官评价。结果对比超市现有绿颜色蔬菜的包装薄膜,在LDPE薄膜中添加适量转光剂可以达到保护鲜切西兰花品质、延长其货架寿命的效果。结论添加质量分数为1.2%单基双能转光剂的低密度聚乙烯薄膜的保鲜效果最好。     

Quality of orange juice in barrier packaging material

The vitamin C content and the colour of orange juice made from concentrate were measured during 9 months of storage at 20°C either under artificial light or in darkness. The packaging materials used were glass, standard monolayer polyethylene terephthalate (PET) and multilayer PET (PET/nylon and oxygen scavenger/PET) containers. In this experiment, all bottles were sealed with aluminium foil in order to avoid any cap effect. The results showed that in plastic packaging materials, the loss of vitamin C was related to the oxygen permeability, and that glass provided the best preservation of ascorbic acid. No statistical difference (p < 0.05) was revealed between the vitamin C content in the juice stored under artificial light or in darkness, whatever the packaging used. The modification of colour was studied with the L, a* and b* values during storage at 20°C under artificial light. L and b* decreased, revealing a reduction of lightness and yellow colour of the juice, whereas a* increased, due to the formation of brown pigments. This change in colour was partly related to the oxygen permeability of the packaging used. The losses of aroma compounds by permeation through the bottle (PET) and the cap (high‐density polyethylene, HDPE) have also been investigated. The results showed that permeation mainly took place through the cap. The use of a multilayer cap [HDPE with internal barrier layer of low‐density polyethylene (LDPE)/EvOH/LDPE] considerably limited the permeation of the aroma compounds studied, whatever the PET bottle used. Copyright © 2007 John Wiley & Sons, Ltd.     

Fabrication and Properties of Antioxidant Polyethylene‐based Films Containing Marigold (Tagetes erecta) Extract and Application on Soybean Oil Stability

Four films were extruded in a pilot‐plant scale blown extrusion machine: a monolayer low‐density polyethylene (LDPE) film added with 2.90% of marigold (Tagetes erecta) extract, a two‐layer high‐density polyethylene/LDPE film added with 3.59% of the extract in the LDPE layer and the corresponding two control films without addition of the extract. More than 64% of astaxanthin contained in the extract was lost during the extrusion process. Spectroscopic, optical and mechanical properties of the films were affected by the addition of the marigold extract. The films showed to be light sensitive when exposed to commercial light at 25 °C; however, bags made of the films showed a positive effect on soybean oil stability when used as packaging. Copyright © 2012 John Wiley & Sons, Ltd.