Effect of packaging oxygen transmission rate on the shelf life of ready-to-heat foods susceptible to postcontamination during refrigerated and illuminated storage

Since more and more pressure is exerted to reduce the use of plastic packaging materials, optimizing the use of food packaging is opportune. The aim of this study was to evaluate the combined effect of packaging materials, spanning a range of oxygen transmission rates (OTR), and retail illumination, on the microbial shelf life and safety of refrigerated ready-to-heat foods. Cooked potato slices were packaged in OPA/PP bags with a high OTR (28.85 ccO₂/m²/d) and OPA-EVOH/PP bags with a low OTR (6.57 ccO₂/m²/d). Cooked composite meals were packaged in tray and foil combinations, also spanning a range of OTR: PP trays (2.09 ccO₂/tray/d) with OPA/PP foils (28.85 ccO₂/m²/d), PP trays with OPA-EVOH/PP (6.57 ccO₂/m²/d) foils, and PET trays (0.07 ccO₂/tray/d) with PET top foil (32.86 ccO₂/m²/d) . The packages were stored in a dark environment, or under fluorescent or LED light. Due to the rapid growth of lactic acid bacteria, the microbial shelf life of both food products was largely unaffected by the type of barrier. Illumination at 1000 lux for 12 hours per day led to temperature differences significantly affecting microbial growth. Based on the results, it could be concluded that re-evaluating packaging material choices for these foods may prove valuable, since the use of high-barrier multilayer packaging materials may be considered as a case of overpackaging.     

改性纳米SiO_2/尼龙复合塑料性能的研究

采用熔融共混法制备改性纳米SiO2/PA6复合塑料,研究了纳米SiO2用量及其粒径对SiO2/PA6复合PA6力学性能、耐热性能和阻隔性能的影响。结果表明:纳米SiO2粒子在纳米SiO2/PA6复合材料中的分散增强了树脂之间的作用力;在一定范围内,随着纳米SiO2用量的增加,改性纳米SiO2/PA6的耐冲击性能、弯曲强度、拉伸强度和耐热性均有一定提高,而纳米SiO2粒径越小,力学性能提高就越显著;当纳米SiO2质量分数为2%~3%时,改性纳米SiO2/PA6透氧性最小,当纳米SiO2质量分数为3%~4%时,改性纳米SiO2/PA6透湿性最小。     

Effect of plastic coating on the sensory properties of fibreboard-based packaging materials in microwave oven heating

The effects of the type and thickness of plastic coating on the migration of off-odours and off-flavours from fibreboard materials to certain model foodstuffs were studied in microwave oven heating. Correlations between sensory, physical and chemical properties of fibreboard materials were also determined. The plastic coating served as a very good barrier to the transfer of off-flavours into foodstuffs. Polyester coating prevented the migration of off-flavours, whereas polyethylene and polypropylene were effective only in certain cases. With the last two plastics, the thickness of the coating layer also affected the amount of off-flavours migrating. Generally, the sensory properties of the materials did not correlate with either the melting behaviour of the plastic coating or the amount of volatile compounds generated.     

Effects of film forming and hydrophobic properties of starches on surface sized packaging paper

The effect on mechanical and barrier properties upon addition of glycerol to temperature‐responsive hydrophobically modified (HM) potato starch was studied on free films. The addition of glycerol lowered the glass transition temperature, the storage modulus, and the water vapor permeability (WVP) for the HM starch films. The HM starch phase separates upon cooling below an upper critical temperature into a solid and a liquid phase. Adding glycerol to the warm starch solution had an inhibiting effect on the particulate precipitation. Substrates surface sized with HM starch with various amounts of glycerol were investigated with respect to barrier properties; WVP, contact angle and Cobb values. Hydroxypropylated starch was used as a reference. Cobb values and WVP results on surface‐sized substrates indicated that the film formation properties of the starches were of great importance for the final surface properties. Good film formation properties were essential for the gas barrier and water resistance while they were less important for high contact angles. The WVP decreased as the glycerol content of the sizes increased, but no sufficient water vapor barrier could be obtained. The HM starches investigated in this work provided good oxygen barrier and the contact angles indicated a hydrophobic character of the surface. The role of the precipitate was investigated, and surface sizing with the precipitate gave low WVP and high contact angles despite its poor film‐forming properties under the experimental conditions. Cobb60 values were slightly improved for HM starch with increasing glycerol content over glycerol‐free sizing. Copyright © 2007 John Wiley & Sons, Ltd.     

Effects of B-ionizing radiation on the properties of flexible packaging materials

The influence of B-ionizing radiation on chemical structure and mass transfer phenomena was studied in the principal flexible food packaging materials (LDPE and OPP). No significant changes were observed in the structure of polymer matrices or in oxygen permeability and global migration after ionizing the materials at dose levels approved for food products ( < 110 kGy). Nevertheless, at low doses, it was observed that volatile organic compounds were present in ionized films. Several oxidation products were analysed by a dynamic head space technique. These oxidation products (typically ketones, aldehydes and carboxylic acids) could play a part in the organoleptic properties of prepackaged foods and, consequently, in their shelf-life.     

Effect of chitosan coating and vacuum packaging on the quality of refrigerated grilled pork

The effects of chitosan coating and vacuum packaging on the quality and shelf‐life of retail packaged grilled pork in a PVDC/nylon pouch during refrigerated storage at 2 ± 1°C were investigated. Grilled pork without chitosan coating and packaged in 100% air was used as the control sample. Firmness, pH, colour, peroxide values, microbial population and shelf‐life (as determined by sensory characteristics) of the samples were determined during the storage. The results showed that colour, peroxide values and microbial population coincided with sensory characteristics. The delayed growth of microbes in vacuum packaging can be attributed to inhibition by low levels of O₂. Chitosan coating was shown to minimize oxidation, as reflected by the peroxide values, colour changes and microbial counts of the samples. Vacuum‐packaged chitosan‐coated grilled pork showed negligible microbial growth and was found to be organoleptically acceptable throughout the storage period. Chitosan coating along with vacuum packaging provided a type of active packaging to maintain quality and extend the shelf‐life of grilled pork. Copyright © 2006 John Wiley & Sons, Ltd.     

4A分子筛对MPP阻燃PA6性能的影响

以恒温聚合得到的三聚氛胺聚磷酸盐(MPP)为阻燃剂,4A分子筛为协效剂,制备了阻燃PA6.研究了4A分子筛用量对阻燃PA6性能的影响.结果表明,少量的分子筛便可以显著提高PA6的阻燃性能,在加速体系成炭的同时使炭层结构发生变化.当MPP、4A分子筛质量分数分别为20%、4%时,阻燃PA6的氧指数可以达到30%,拉伸强度...     

Effect of modified atmosphere packaging and superchilled storage on the shelf‐life of farmed ready‐to‐cook spotted wolf‐fish (Anarhichas minor)

Modified atmosphere packaging (MAP) combined with superchilling (?1°C) was evaluated as a mild preservation method for farmed spotted wolf‐fish (Anarhichas minor). Portions were packaged in air and in CO2:N2 (60%:40%) atmosphere with a gas:product ratio of approximately 1, at superchilled (?1.0°C ± 0.2°C) or chilled (+4.0°C ± 0.2°C) temperatures. A reduced bacterial growth (p < 0.001), measured as aerobic plate counts (APC) and psychrotrophic bacteria, was observed in modified atmosphere (MA) packaged wolf‐fish at both ?1°C and +4°C, compared to portions in air. MA‐packaged wolf‐fish had improved odour and flavour scores (p < 0.05), but also a higher drip loss than fish stored in air. A shelf‐life of 15 days was obtained at ?1°C for MA‐packaged fish compared to 8–10 days in air, and at 4°C the shelf‐life was 13 days in MA and 6–8 days in air. Copyright © 2006 John Wiley & Sons, Ltd.     

LDPE-Ni/多晶铁纤维电磁屏蔽包装材料研究

为制备一种性能优良,使用方便的电磁屏蔽包装材料,用多晶铁纤维和镍粉作为导电填料,填加到LDPE中,制备成了LDPE-Ni/多晶铁纤维电磁屏蔽材料.研究发现,该材料的屏蔽效能值为20dB;"渗滤阈值"为20%～25%;由于多晶铁纤维的复合磁损耗机理,材料的具有一定的吸波功能;当多晶铁纤维和镍粉的含量为18%时,复合材料达到最大拉伸强度12.5MPa,而其断裂伸长率呈下降趋势.     

有机蒙脱土对ABS-PA6共混物形态结构与力学性能的影响

熔融挤出制备了不同有机蒙脱土(OMMT) 含量的OMMT/丙烯腈-丁二烯-苯乙烯(ABS) -尼龙6 (PA6) (30/70,质量比) 复合材料,用透射电子显微镜(TEM),扫描电子显微镜(SEM) 等研究了OMMT在ABS-PA6共混物中的分布及其对ABS-PA6共混物形态结构与力学性能的影响。结果表明:在OMMT/ABS-PA6复合材料中,OMMT主要以剥离形态分布在PA6基体相中,少量分布在PA6与ABS两相界面处,具有明显的选择分布性;随着 OMMT含量增加,ABS分散相尺寸逐渐减小且分布均匀OMMT/ABS-PA6 复合材料的强度、模量逐渐提高,当OMMT含量为7 wt%时 , 弯曲强度和模量分别由未加OMMT时的66. 7 MPa、2. 308 GPa上升至94. 1 MPa、3. 184 GPa,缺口冲击强度在OMMT含量为3 wt%时出现极大值3. 7 kJ / m,但总体变化不大。      

聚碳酸酯/尼龙6共混体系力学性能的研究

探讨了不同增容剂对PC／PA共混体系的影响，研究结果表明：苯乙烯－马来酸酐共聚物（SMA）对PC／PA共混体系有一定增容作用，加入少量SMA后，共混物的力学性能有所提高；自制增容剂B与SMA协同使用对PC／PA共混体系有较好增容作用，协同增容后共混物的冲击强度大幅度提高，同时共混物仍保持较高的拉伸强度和弯曲强度。     

High‐pressure processing effects on the mechanical,barrier and mass transfer properties of food packaging flexible structures: a critical review

Food products can be high‐pressure processed (HPP) either in bulk or prepackaged in flexible or semi‐rigid packaging materials. In the latter case the packaging material is subjected, together with the food, to high‐pressure treatment. A number of studies have been performed to quantify the effects of high‐pressure processing on the physical and barrier properties of the packaging material, since the integrity of the package during and after processing is of paramount importance to the safety and quality of the food product. This article reviews the results of published research concerning the effect of HPP on packaging materials. Copyright © 2004 John Wiley & Sons, Ltd.     

Effect of high‐pressure processing on the mechanical and barrier properties of selected packagings

This investigation focuses on the effect of high‐pressure processing (HPP) on possible changes of the mechanical properties and of the water vapour permeability of seven selected packaging materials. NOD 259 (PA‐PE), BB4L (Cryovac‐Grace packaging), PET/BOA/PE, PET/PVDC/PE, PA/SY, LDPE and EVA/PE were investigated (PET, polyester; PE, polyethylene; SY, surlyn; LDPE, low‐density polyethylene; EVA, polyethylene–vinyl acetate co‐polymer; BOA, biaxially oriented polyamide). These packaging materials were selected because of their interest to the food industry. All had an internal film of PE for food use. High‐pressure tests were realized at 10°C for 10 min at pressures of 200, 400 and 600 MPa, with water as a food‐simulating fluid. The depressurization rate was either rapid (pressure drop in <10s) or slow (20 MPa/min). Permeability to water vapour was realized using the NFF H 00 030–ASTM E96‐90 standard. Mechanical tests were carried out with a tensile testing machine (Lloyd LR5K), according to the NF 54‐102 standard. Maximal stress, rupture stress and strain at rupture were evaluated with non‐treated and treated samples. Obtained results showed that HPP minimally affects the mechanical strength of packaging material. The depressurization rate did not have any significant influence in our conditions. The barrier properties to water vapour were not significantly affected and were even slightly enhanced for LDPE, which is a packaging material commonly used for HPP applications and at least as a food contact material. Copyright © 2006 John Wiley & Sons, Ltd.     

Effect of light‐barrier property of packaging film on the photo‐oxidation and shelf life of cookies based on accelerated tests

The influences of intensity of ultraviolet (UV) light, light‐barrier property of packaging film on the fat photo‐oxidation and accelerated shelf life of cookies were studied. Unpacked cookies were stored at a temperature of 408C and a relative humidity (RH) of 50% for 10 to 65 days, with an intensity of the UV light of 0.3, 1.9 and 9.5 mW/cm². Meanwhile, the same batch of cookies was packed with oriented nylon/polyethylene, polyethylene terephthalate/oriented nylon/polyethylene and bi‐oriented polypropylene/vacuuming aluminized casting polypropylene and stored at the same temperature and RH and UV‐light intensity of 1.9 mW/cm² for more than 40 days. The peroxide values (POV) of cookies were measured under the storage conditions. The results showed that the intensity of the UV light and light‐barrier property of film had notable influence on the photo‐oxidation rate and accelerated shelf life of cookies. According to the threshold of POV, unpacked cookies were rancid less than 32 and 11 days when exposed in light of 1.9 and 9.5 mW/cm² in the accelerated test, respectively. In contrast, the shelf life of unpacked cookies in darkness, or cookies packed in high light‐barrier package was more than 75 days. Logarithm of POV and store‐time relationship under different UV‐light illumination was successfully fitted by linear regression under the same temperature, RH and the accelerated shelf‐life‐based oxide index was estimated. Copyright © 2008 John Wiley & Sons, Ltd.     

Role of ex-situ oxygen plasma treatments on the mechanical and optical properties of diamond-like carbon thin films

Role of ex-situ oxygen plasma (OP) treatment on mechanical properties of diamond-like carbon (DLC) thin films is explored. The DLC film after this treatment shows superhardness behaviour, maximum hardness of 46.3 GPa and elastic modulus of 423.2 GPa are obtained when film grown at self bias of 100 V followed by 10 min OP treatment. Moreover, the colour of the coating is fed after OP treatment, leading it to a colourless coating with significantly enhanced transmittance and improved antiglare property. Such OP treated DLC films may find their applications as protective coatings on cutting tools, automobile parts, magnetic storage media and colourless coating in packaging, as the DLC films posses brown colour.     

PA6/EPDM-M/CaCO3三元复合材料力学性能影响因素研究

通过两步法工艺制备了PA6/EPDM-M/CaCO3三元复合材料,并研究了CaCO3粒径、CaCO3用量、EPDM-M用量及预混时间对该复合材料力学性能的影响。研究表明CaCO3粒径对复合材料的力学性能影响最大,尤其是冲击性能。并采用SEM观察了试样的冲击断面,结果显示,含CaCO3粒径较小的复合材料在受到外力冲击时发生明显的塑性变形,断面呈现微纤化,具有较高的冲击强度。     

热处理对碳纤维/聚酰胺6复合材料界面结晶及力学性能的影响

探究了热处理对聚酰胺6（PA6）在碳纤维（CF）表面的结晶行为及其界面力学性能的影响。利用差示扫描量热法（DSC）、偏光显微镜（POM）观察法等分析手段考察了热处理对PA6在CF表面结晶行为的影响,揭示了在热处理过程中,PA6进行链段重排,形成小且不完善的新结晶,导致结晶度的上升以及界面横晶形貌的完善;进一步通过单丝微球脱粘实验和单向CF/PA6复合材料横向拉伸实验考察了热处理对PA6与CF的界面结合性能的影响,揭示了经退火热处理的试样由于弱界面和应力集中的减少使界面剪切强度增加且单位体积断裂能下降。     

Study of the effective parameters on mechanical and electrical properties of carbon black filled PP/PA6 microfibrillar composites

In this study the electrical and mechanical properties of microfibrillar polypropylene (PP)/polyamide6 (PA6) blend filled with super conductive carbon black (CB) have been investigated. In situ microfibrillar PP/PA6 composites filled with CB are produced using a single screw extruder equipped with a spinneret. Glycidyl methacrylate (GMA) grafted polypropylene (PP-g-GMA) is used as the compatibilizer. To investigate the effects of extensional flow on the microstructure, electrical and mechanical properties, three adaptors with various convergence angles were designed, prepared and applied between the extruder and the spinneret. To optimize the effects of processing and material parameters on the electrical and mechanical properties, the Taguchi method of experimental design is used. Material and processing factors which are studied include: concentration of PA6, compatibilizer level, CB concentration, drawing speed of melt spinning line, adaptor angle, order of mixing and temperature profile along the extruder. The results show an increase in DC conductivity of up to 10¹¹ times in comparison with pure PA6, by increasing the concentration of CB, drawing speed, adaptor angle and optimizing other parameters. By optimizing processing and material factors studied here, strength of microfibrillar structured composites is increased of up to 80% in comparison to pure PP.     

Influence of the annealing in nitrogen atmosphere on the XRD, EDX, SEM and electrical properties of chemical bath deposited CdSe thin films

The influence of annealing in nitrogen atmosphere on the structure, optical and electrical properties of cadmium selenide (CdSe) thin films deposited by chemical bath deposition (CBD) onto glass substrates was studied. The samples were annealed in nitrogen atmosphere at various temperatures. A transition from metastable nanocrystalline cubic to stable polycrystalline hexagonal phase has been observed after annealing. The as-deposited CdSe thin films grow in the nanocrystalline cubic phase with optical band gap 1.93 eV. The electrical resistivity of the thin films has been measured in order of 10⁶ Ω cm. The activation energy of the samples has been found to be 0.26–0.19 eV at low temperature region, and 0.36–0.56 eV at high temperature region. It was also found that the activation energy and the resistivity of the films decrease with the increasing annealing temperature.     

汉麻纤维表面改性对其增强聚丙烯复合材料性能及挥发性有机化合物释放影响

通过非织造-热压工艺制备了汉麻纤维增强聚丙烯（HF/PP）复合材料。采用热重-质谱联用仪（TG-MS）研究了HF/PP复合材料的挥发性有机化合物（Volatile organic compounds,VOC）释放来源及汉麻经聚乙烯醇（PVA）改性和尿素改性对HF/PP复合材料VOC释放的影响,同时研究了两种改性方法对HF/PP复合材料热学性能和力学性能的影响。结果表明：HF/PP复合材料中的VOC主要来源于汉麻纤维,改性后的HF/PP复合材料力学性能相比未处理的均有不同程度的提升,尿素改性后,HF/PP复合材料的拉伸强度和弯曲强度达到最大值,较未处理时分别提升了19.32%和15.04%。PVA改性后,HF/PP复合材料的拉伸模量、弯曲模量和剪切强度达到最大值,相比未改性时分别提升了17.72%、15.94%和24.72%。改性后HF/PP复合材料热稳定性能和VOC释放相较未处理时均得到了优化：PVA改性后HF/PP复合材料热稳定性最优,三个阶段总活化能较未处理时提高了121.99%,达到了392.56 kJ·mol^-1,并且HF/PP复合材料热稳定性与界面性能密切相关;尿素及PVA改性后HF/PP复合材料的总VOC（TVOC）释放量相较未处理时均降低。