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.     

The influence of α‐tocopherol concentration on the stability of linoleic acid and the properties of low‐density polyethylene

In food packaging applications where low‐density polyethylene (LDPE) film containing α‐tocopherol is used, the antioxidant may have a dual function, i.e. to protect the polymer from oxidative degradation during processing, and to delay the onset of oxidation of the packaged foodstuff during storage. Incorporation of high levels of α‐tocopherol into LDPE film was found to inhibit oxidation of a linoleic acid emulsion stored in contact with the film at 6°C. However, the presence of 360 ppm caused changes in mechanical properties and an increase in oxygen transmission. Levels as high as 3400 ppm α‐tocopherol also caused yellowing and reduction in crystallinity of the material. Thus, the use of high amounts of α‐tocopherol in LDPE, which might be needed in active packaging applications, requires careful consideration of the protective requirements for each specific food and the maintenance of the desired properties of the packaging material. Copyright © 2000 John Wiley & Sons, Ltd.     

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.     

Preparation and properties of sodium bicarbonate‐incorporated LDPE films with deodorizing function for kimchi packaging

Volatile compounds produced during the fermentation of kimchi result in a sour taste and unpleasant odor. Here, we evaluated the utility of sodium bicarbonate (baking soda) as a natural deodorant in kimchi packaging. Baking soda decomposed into sodium carbonate, which showed superior deodorizing effects at 180°C, and aroma patterns were altered after deodorizing treatment with baking soda and heat‐treated baking soda. Moreover, the numbers of off‐odor compounds were decreased when using baking soda or heat‐treated baking soda. In addition, the acetic acid removal rate increased with heat treatment of baking soda. Notably, the external shape and color of baking soda particles were not affected by heating. It was observed that an increase in the content of baking soda in the low‐density polyethylene (LDPE)/baking soda composite films enhanced deodorizing effects. Finally, sensory evaluation confirmed that odor decreased with increased baking soda content. The findings demonstrate the potential value of baking soda and LDPE/baking soda composite films in kimchi packaging and reduction of off‐odors.     

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.     

二氧化硫缓释杀菌包装在“夏黑”葡萄保鲜中的应用研究

目的延长"夏黑"葡萄在常温条件下的货架期。方法以裸放和普通LDPE包装作为参照组,对比研究了SO2缓释杀菌包装、添加1-MCP的SO2缓释杀菌包装等2种保鲜包装方案对葡萄货架期的影响。实验中每2 d分别对包装袋内的顶空气体组成,葡萄的外观质量、水分损失、褐变程度、硬度、糖分、总酸含量和VC含量进行测试分析。结果 SO2缓释杀菌包装能够形成适合葡萄贮藏的自发气调氛围,并且能够抑制葡萄霉菌的滋生。常温保存8d后,裸放组和LDPE组的果梗褐变和烂果严重,而SO2缓释杀菌包装、添加1-MCP的SO2缓释杀菌包装中葡萄褐变程度分别为1级和0级,烂果率分别为3.13%和1.1%。结论 SO2缓释杀菌包装中葡萄的外观和口感均具有商品性,保鲜效果明显。     

Effect of packaging film on the quality of ‘Chaoyang’ honey peach fruit in modified atmosphere packages

The quality of honey peach fruit stored at 2°C in modified atmosphere packages was studied. Three different thickness low‐density polyethylene (LDPE) films were used as packaging films. Honey peach fruits of ‘chaoyang’ were packaged in LDPE bags 15, 25 and 40µm thick and control (air). The respiration rate, O₂ and CO₂ concentrations in the packages, flesh colour, total soluble solid (TSS), titratable acidity (TA), flesh firmness (FF) and membrane integrity of the fruits were monitored. Compared to the control, MAP treatments inhibited the climacteric peak, avoided the increase of flesh colour, decreased the development of softness and retarded the reduction of TTS, TA and membrane integrity. Significant differences in the quality of the fruits were found between the three packages and the control (p ≤ 0.05). After 20 days at 2°C within the LDPE25 bags, a steady‐state atmosphere of 5% CO₂ + 4% O₂ was reached. Honey peaches stored in these bags showed the best quality at the end of the storage. Copyright copy; 2006 John Wiley & Sons, Ltd.     

Preservation of cold‐stored guavas influenced by package materials

The objective of this study was to evaluate the influence of package materials on the preservation of cold‐stored ‘Kumagai’ guavas. The treatments were: PO2, co‐extruded polyolephinic film with gas injection (5% O₂/5% CO₂/N₂); PO3, co‐extruded polyolephinic film with gas injection (5% O₂/5% CO₂/N₂); LDPE, linear low density polyethylene film; LDPE‐gas, linear low density polyethylene film with gas injection (3% O₂/8% CO₂/N₂); PVC, polyvinylchloride stretch film; PO1, co‐extruded polyolephinic film and control: non‐packaged guavas. Guavas were stored at 10 ± 1°C/80–90% RH for 21 days, and then transferred to room temperature. Gas composition within the package headspace was analysed during storage and the physical and chemical characteristics of the guavas were evaluated daily during ripening. The modified atmosphere provided by PO1 film was insufficient to promote the benefit of senescence control. Although PVC provided an atmosphere close to that recommended, it did not preserve the colour and pulp firmness. PO2, PO3, LDPE and LDPE‐gas retarded the senescence process of the guavas during 21 days at 10°C plus 2 days at room temperature, but harmed the normal ripening of guavas in some aspects. This can be explained by reduced O₂ and elevated CO₂ levels within these four packages. None of the packages influenced the titratable acidity and the soluble solids, but they did harm ascorbic acid synthesis. Copyright © 2005 John Wiley & Sons, Ltd.     

Development of electronic nose method for evaluation of residual solvents in low‐density polyethylene films

Flexible packaging films containing high levels of residual volatile organic compounds (VOCs) can alter the flavour and odour of packaged foods. Currently, a range of gas chromatographic techniques and sensory evaluations are used for assessing the residual VOCs in packaging films. An objective method for assessing the residual solvents from low‐density polyethylene (LDPE) was developed using an Alpha MOS Fox 3000 electronic nose (e‐nose) equipped with 12 metal oxide semiconductor sensors. Three VOCs, ethyl acetate, ethyl alcohol and toluene, were chosen as models for solvents of interest in flexible food packaging analysis. LDPE film samples were spiked with single and binary mixtures of solvents and analysed using the e‐nose and by GC–FID (HP 6890; Hewlett‐Packard Co., Wilmington, DE). The responses obtained from the e‐nose were processed using principal component analysis (PCA) and discriminate factorial analysis (DFA) in order to identify the residual solvents. Partial least squares analysis (PLS) was also used to quantify the amount of residual solvent and to correlate the e‐nose results with gas chromatography, which is currently the standard method for determining residual VOCs in packaging films. There was good agreement between the e‐nose responses and gas chromatography results for single solvents (r = 0.90–0.98). The technique also worked for binary solvent mixtures (r = 0.84–0.99). The electronic nose can be a viable alternative to traditional techniques while providing simplicity and objectivity, which would be extremely advantageous in routine quality control of residual solvents. Copyright © 2006 John Wiley & Sons, Ltd.     

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.     

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.     

Evaluation of plastic packages for guava refrigerated preservation

Guavas cv. ‘Kumagai’ were packed in several plastic materials and stored at 10°C and 85–90% relative humidity (RH) for 7, 14, 21 and 28 days (+3 days at 25°C). The plastic materials studied were: multilayer co‐extruded polyolephine film with selective permeability (PSP), low‐density polyethylene film (LDPE), LDPE film with mineral incorporation (LDPEm) and heat‐shrinkable polyolephine film (SHR). Guavas not packed were taken as control samples. The physicochemical characteristics of the fruits, O₂ and CO₂ transmission rates of the packaging materials and gas composition at the package headspace were evaluated. The LDPE film, 69 µm in thickness, with the lowest permeability to both O₂ and CO₂, led to anaerobiosis and high CO₂ concentration inside the packages and promoted physiological disturbances and changes in fruit flavour. The SHR film, 15 µm in thickness, was the most permeable to CO₂ and had quite high O₂ transmission, which modified the inner atmosphere of the packages slightly. The fruits packed in this film showed a poorer quality than the controls, possibly due to the heat produced during the shrinking of the film. The LDPEm film, 24 µm in thickness, was almost as permeable to CO₂ but had reduced O₂ transmission, promoting an atmosphere of equilibrium of 3% O₂ and 4.5% CO₂. Fruits packed in this film kept their skin colour and pulp firmness, suitable for consumption up to 14 days. The PSP film, 35 µm in thickness, had the greatest O₂ transmission but just over half of the CO₂ transmission of LDPEm, promoting an atmosphere of equilibrium of 0.5% O₂ and 4.5% CO₂ inside the packages. Fruits packed in such packages kept their physicochemical characteristics up to 21 days. Copyright © 2001 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。     

Wear resistance and wear mechanisms in polymer + metal composites

We have investigated composites containing metallic micro-size and nano-sized particles as the 10 wt% dispersed phase. Branched low density polyethylene (LDPE) was the matrix. Microsized metals were Al, Ag and Ni; nanosized metals were Al and Ag. Several mechanisms of wear are observed in function of the kind and size of metal used: deformation, delamination, abrasion, adhesion and rolls formation. The presence of Ag particles increases the wear rate as compared to neat LDPE. The presence of Al particles lowers the wear of LDPE significantly; nanoparticles are more effective than microparticles.     

Tuned optical properties of in-situ synthesized m-nitroaniline doped Ag/PVA nano-composites

Meta-nitroaniline (m-NA) doped silver/poly(vinylalcohol) (Ag/PVA) nanocomposites are prepared via in-situ reduction of silver salt by employing hydrazine hydrate (HH) in order to study the effect of the NLO active m-NA on the optical properties of nanoparticles of silver in the colloidal as well as self supported film form. Reduction of silver salt in aqueous alcoholic PVA with HH is done first followed by doping of the reaction mixture with m-NA. The UV-Visible absorption spectra show peak at about 400 nm for Ag nanoparticles due to surface plasmon resonance phenomenon, which gets blue shifted with the change in m-NA concentration. The Second Harmonic Generation (SHG) studies show improvement in intensity with increasing m-NA concentration up to a saturation point (approximately 2.52 wt% with respect to PVA). Further increase in m-NA concentration leads to decrease in SHG intensity. The solutions and the films are characterized by photoluminescence (PL), FTIR spectroscopy, XRD, SEM, TEM, and thermal analysis. m-NA doped composites showed better PL efficiency. SEM of the nanocomposite film shows uniform distribution of particles within the film. The particle size as shown by TEM is found to be less than 10 nm.     

Preparation and sintering properties in air of silver-coated copper powders and pastes

In this paper, uniform and well dispersed silver-coated copper powders were prepared by replacing reaction at first. The structure and properties of the bimetallic powders were investigated by XRD, SEM and TGA. It was found that anti-oxidization of the silver-coated copper powders increased with the increase of the silver content slightly and a dense coating surface was observed at Ag content of 53.9 wt%. Furthermore, the pastes with relatively low silver content which were prepared from silver-coated copper powders, displayed high conductivity similar to pure silver even after sintering in air. And their sintering properties were also investigated at different temperature in air atmosphere. The film exhibits good electrical properties at sintering temperature between 800 and 900 °C. When the paste from silver-coated copper powder with Ag content of 53.9 wt% was printed on Al₂O₃ substrate and sintered at 800 °C in air, the sheet resistance of the film is 0.036 Ω/□ only.     

Development and characterization of PET/Fish Gelatin–nanoclay composite/LDPE laminate

A three‐layer laminate film was developed with the following structure: polyethylene terephthalate (PET)/fish gelatin (FG)–nanoclay composite/low‐density polyethylene (LDPE). The FG–nanoclay composite material functioned as the oxygen barrier layer and demonstrated comparable oxygen barrier properties when compared with a similar laminate utilizing ethylene vinyl alcohol as the barrier layer at a relative humidity (RH) of up to 50%. The introduction of nanometer‐sized filler clay into the FG matrix lowered the oxygen permeability (OP) because of the tortuosity effect of the clay particles. In addition, the FG–nanoclay composite film exhibited bond strengths similar to both LDPE and PET. The hydrophilic nature of FG significantly increases OP under high (>50%) RH conditions. However, this new FG laminate film could be a possible alternative for packaging designers desiring a more sustainable packaging material for low‐RH (<50%) applications. Copyright © 2009 John Wiley & Sons, Ltd.     

Active packaging technology to retain storage quality of pear cv. “Bartlett” during shelf-life periods under ambient holding after periodic cold storage

Response of “Bartlett” pears harvested at commercial maturity (104.29-N firmness and 3.15 starch iodine rating) to various active packaging conditions using O₂ (Fe powder) and ethylene (KMnO₄) scavenger sachets in low-density polyethylene (LDPE) film bags (25.4 and 50.8 μm), cold storage (2 ± 1°C with 95 ± 2%), and shelf-life holding periods under ambient conditions (24 ± 3°C; 68 ± 5% relative humidity [RH]) was recorded as changes in physic chemical parameters. The fruits were packed in 25.4- and 50.8-μm LDPE film bags containing 5%, 10%, and 15% Fe and KMnO₄ powder incorporated on silica as inert carrier in form of sachets. After packaging the fruits airtight in film bags, they were placed in corrugated fiber board (CFB) boxes (29 × 23 × 14 cm; L × B × H). Fruits packed in 50.8-μm LDPE film bags with sachets containing 15% Fe powder recorded maximum fruit firmness, total soluble solids (TSS), titratable acidity, and ascorbic acid with minimum spoilage, weight loss (physiological loss of weight [PLW]), pectin methylesterase (PME), polygalacturonase (PG) activity, and respiration rate and increase in fruit calcium content and highest level of overall acceptability (color, taste, aroma, and texture) after periodic cold storage and ambient shelf-life periods. The effect of different treatments was compared by post hoc analysis using Tukey's test, which also revealed significant differences among different treatments. Our findings also revealed that pear fruit retains edible quality until fruit firmness > 30.89 N, TSS > 10.0%, and weight loss < 9.00%.     

Effects of Packaging and Preservation Treatments on the Shelf Life of Murtilla Fruit (Ugni molinae Turcz) in Cold Storage

Murtilla (Ugni molinae Turcz) fruit has a unique aroma; along with its pleasant sweet flavour, this has stimulated its commercial development in international markets. This development, however, requires the application of suitable conservation methods. Five different packaging treatments for murtilla fruit (Red Pearl‐INIA variety) conservation were evaluated at 0 °C for 60 days. The treatments consisted of two types of packaging [polyethylene terephthalate (PET) punnets and low‐density polyethylene (LDPE) bags] and the application of an edible coating of carboxymethyl cellulose to the fruits. The incorporation of the aqueous extracts of murtilla leaves from the 18‐1 and 27‐1 ecotypes into the carboxymethyl cellulose edible coating was also evaluated for its antimicrobial effects. There was a significant (p < 0.05) reduction in the moisture content, a significant weight loss and an increase in soluble solids when the murtilla fruit was packed only in a PET punnet. However, with the other four treatments, in which an LDPE bag and edible coating were used, the moisture content (76.8–74.4 g/100 g) and soluble solids (15.6–17.8 ºBrix) in the fruit remained stable during storage. Low weight loss (1.64–2.25%) occurred in the fruits that received treatments with the LDPE bag and edible coating. Under experimental conditions and from operational facilities, packaging in PET punnets with an LDPE bag was the best alternative to preserve the murtilla fruit at 0 °C for 60 days. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of light and oxygen transmission characteristics of packaging materials on photo‐oxidative quality changes in semi‐hard Havarti cheeses

Changing transmission characteristics of food packaging materials by colouring the materials may be a suitable way of reducing photo‐oxidative quality changes. This study proved that packaging in black laminates provided the best protection of Havarti cheese, followed by a white laminate. However, transparent packaging materials did not protect the product in the critical wavelength range, i.e. 400–500 nm, and changes in colour and odour were already notable after few hours of exposure to fluorescent light. Additionally, secondary oxidation products, hexanal, 1‐pentanol, and 1‐hexanol, were formed in cheese packaged in transparent or semi‐transparent packaging materials. The expected effects of oxygen transmission were difficult to evaluate, due to high residual oxygen levels in the packages. Copyright © 2002 John Wiley & Sons, Ltd.