The effect of microhole size and foodstuff on the microbial integrity of aseptic plastic cups

Penetration of a motile microbe, Enterobacter aerogenes, was investigated through aseptic packages filled with milk, meat soup, sausage gravy and soft agar. Penetration was dependent on the microhole diameter and on the viscosity of the foodstuff in the package. The smallest microhole diameter permitting the passage of E. aerogenes in this study was 5 μm when the packages were filled with milk and the microhole length was 40 μm. While the packages were filled with soft agar, meat soup and sausage gravy, the smallest penetrable microhole was 10, 20 and 25 μm in diameter, respectively. On the other hand, even the microholes of 100μm diameter were not penetrated by E. Aerogenes in every package tested. This may have been owing to blockage of the microholes by the test foodstuff thus hindering the penetration of bacteria.     

Aseptic integrity and microhole determination of packages by gas leakage detection

In principle, an aseptic package should protect against any type of microbe penetration. It means that each microhole must be less than about 0.5μm in diameter. In practice this critical limit may be much higher, owing to various factors, and consequently a controlling system does not necessarily have to have such a sensitivity. Controlling systems based on gas leakage detection have been suggested. In this report the basic validity range of such systems, including either mass spectrometer detection or an infra-red spectrometer, is analysed and various crucial factors are clarified as a basis for technical development. The actual control principle assumes that transmission of gases through the package originates only from microholes and cracks and that gas permeation through the packaging material is negligible. However, in practice the gas permeation may be considerable. For example, a package having a polyethylene (LDPE) barrier layer of 50μm in thickness has a gas permeation comparable to what is coming out through a pinhole of 10μm in diameter, and accordingly only much bigger microholes can be determined, with reference to calculations presented. If the barrier is improved by a Saran® layer (PVDC) of 25μm the gas permeation is still disturbing and only holes bigger than about 5μm in diameter may be detected. If instead the barrier is improved by an aluminium layer, gas permeation is negligible in most cases, and the basic principle of the gas leak detection systems is valid. Infra-red spectrometer based systems theoretically need at least a test time of 0.5 min and in practice much more to detect a microhole of 10μm in diameter-to collect a sufficient quantity of trace gas. Mass spectrometer based systems are in principle not testing time limited assuming a rapid enough vacuum pump can be arranged and that moisture interferences do not arise from the packaging material or from the packaged contents. Further, some aspects on the necessity of introduction a 100% control system, vis-a- vis a statistical control system, are given in terms of producer's and consumer's risks. About 100 packagings/h must be tested at ordinary production speed (1000–3000 packagingslh^?1) to check accepted quality levels of 0.1% defectives. At higher quality levels, i.e. less than 0.1% defectives, the sample size needed increases rapidly towards 100% of the total production.     

Effect of biaxial‐simultaneous stretching conditions on OTR and CO2 permeation of CO2 laser perforated poly(lactic acid) film

The biaxially oriented poly(lactic acid) films prepared using simultaneous biaxial stretching were perforated by CO₂ laser with the power of 60 W. The focal spot diameter was fixed at 103 μm. Pulse durations were varied from 1 to 30 μs, which corresponds to the fluence from 1.4 to 42.6 J/cm². The perforated microhole size increased with increasing laser energy. The shape of microholes was circular for the films of equi‐biaxial stretching, whereas elliptical microholes were formed with its long and short axes corresponding to the directions of higher and lower stretch ratios, respectively. Comparing the laser perforation behavior of the as‐drawn films and annealed films, the opening of a microhole in the annealed films started at higher laser fluence, and at the same fluence the size of microhole was smaller. Gas transmission rates of the biaxially oriented poly(lactic acid) films with different thicknesses were examined. The oxygen transmission rates (OTR) of film improved with increased microhole diameter. The OTR of films containing 1 microhole/103 cm² (hole diameter of ~110 μm) was 184, 150, and 98 cm³/d in comparison with the OTR for the original films without microhole of only 16, 10, and 8 cm³/d, respectively. Packaging films with OTR higher than 100 cm³/d (equivalent to the 9700 cm³/m²/d) are required to create a modified atmosphere inside the package of fresh produce for shelf‐life extension. Measured OTR and CO₂TR values of the 3 different shapes of microhole were compared and discussed.     

Predicting changes in oxygen concentration in the headspace of nitrogen flushed packages by the ambient oxygen ingress rate method

The ambient oxygen ingress rate (AOIR) method is an alternative/supplementary method to Ox‐Tran for measuring the oxygen transmission rates of packages. The AOIR method facilitates high‐capacity testing of packages under realistic food storage conditions, on the one hand, and on the other hand provides the possibility to predict the oxygen concentration over time in packages flushed with nitrogen at the time of packaging. The predicted oxygen concentration values showed good agreement with experimental values for flexible packages stored over a period of 91 days at 23°C and 38°C. The prediction of the oxygen concentration in­nitrogen‐flushed packages may be a useful tool, e.g. in shelf life studies, in the selection of the optimal food package as regards to oxygen protection and within quality control purposes. Copyright © 2002 John Wiley & Sons, Ltd.     

Simple models for evaluating effects of small leaks on the gas barrier properties of food packages

A detailed theoretical analysis and calculations were made for providing a simple and explicit means to evaluate the effects of small leaks on the barrier properties of food packages. Small leaks, such as pinholes and channel leaks, were approximated as cylindrical pores with diameters of 50–300 μm. The first part of the current study proposes a simple mathematical model based on Fick's law of diffusion, which accounts for both the gas leakage across small leaks and the gas permeation across package walls. The model uses an effective permeability that depends on leak dimensions, type of diffusing gas, type of packaging material and gas conditions around the leak ends. In the second part of the study, three practical cases are presented to illustrate the application of the proposed model in examining the significance of leaks. These demonstrate in a simple and explicit manner that for LDPE packages: (a) leaks affect the oxygen transfer more than the water vapour transfer; (b) leak effects are more significant at lower storage temperatures; and (c) that for high gas barrier packages, the effect of leaks is very important and should not be neglected. The model can be also used to arrive at conclusions about the significance of leaks in other packaging situations (e.g. other than LDPE packaging materials) and to correct the shelf‐life estimation of gas‐ and water vapour‐sensitive foods for errors from package leaks. Copyright © 2003 John Wiley & Sons, Ltd.     

微孔膜包装内外气体交换的理论研究

为有效地提高包装膜的透气率,基于原包装膜而进行后加工制孔是近年来采用的主要技术手段之一.探讨了该类型微孔膜的透气机理,基于气体的渗透与粘性流动理论,建立微孔膜硬质盒包装、袋包装内外气体交换模型.理论分析了包装型式、微孔参数对包装内气份变化的影响.结果表明:设置微孔可显著地提高包装内外气体的交换速率;包装型式对包装内气份的变化有影响但不显著;包装膜孔隙率、微孔孔径显著地影响包装内气份变化速率,且孔径大小对包装内气份变化的影响更为显著.     

Flaking failures originating from microholes of bearings under rolling contact fatigue

Rolling contact fatigue tests were carried out using plates with microholes (diameter was about 100 μm and depth was about 140 μm) under three different loads (maximum values of Hertzian stress were about 3250, 3550 and 3840 MPa, respectively) and the surface cracks initiating from those holes were observed. It was found that there is a threshold value of maximum Hertzian stress whether surface cracks originate from microholes or not, and its value is between 3250 and 3550 MPa. However, flaking failures occurred even when the stress values were lower than the threshold value. In order to investigate the relation between the flaking failures and the cracks, sectional observations of the subsurface cracks were made before and after the surface layer separations. From these observations, it was found that the subsurface cracks caused the flaking failures even when the maximum value of Hertzian stress was lower than the threshold value of surface crack initiation.     

Microhole drilling through electrochemical processes: A review

Day-to-day interest is growing in the drilling of high aspect-ratio deep microholes in various hard-to-machine and newer materials. Besides cost-effectiveness in the manufacturing process, an accurate dimension with the good surface finish is essential for microhole drilling. The conventional methods encounter various problems such as residue stresses, heat generation near cutting zone, high tool-wear, etc. Electrochemical microdrilling (ECMD) is one of the cost-effective techniques, provide a better alternative in drilling microholes with reasonably accurate dimensions and good surface finish in various industrial applications especially in computer, electronic, and aerospace industries. This article reviews current researches and developments of electrochemical processes for circular microholes drilling. It highlights the effects of various key factors (such as the development of microtools, electrolyte, inter-electrode-gap monitoring and control, etc.) on the aspect-ratio and accuracy of circular microholes, produced by ECMD. For further research, it will open up various challenging opportunities, especially in the field of (i) development and handling of microtool electrodes, (ii) development and handling of electrolytes medium, (iii) development in monitoring and controlling techniques of inter-electrode-gap, and (iv) development in strategies for process control for drilling high quality, deep and high aspect-ratio circular microholes into hard-to-machine materials using ECMD.     

Evaluation of a laboratory‐scale pressure differential (force/decay) system for non‐destructive leak detection of flexible and semi‐rigid packaging

This study evaluated the capabilities of a bench‐top non‐destructive pressure differential leak tester using 355 ml polyethylene terephthalate/ethylene vinyl alcohol/polypropylene (PET/EVOH/PP) trays. This evaluation was done by monitoring the equipment's force/decay responses to leaks, changes in the package headspace volume and differences in the seal strength of 986 sample trays. Leak detection evaluation was done using artificially created channel leaks (10–200 µm) in the sealing areas and pinholes (5–50 µm) in the lids of the polymeric trays. Seal strength evaluation included the ability of the equipment to identify non‐leaking but weak seals and the extent to which the pressure differential unit affected good seals during a normal test run. The results showed that the equipment had a detection limit of 40 µm for channel leaks 6 mm in length and 15 µm for pinholes. The results also showed that the pressure differential unit caused a 9% reduction in the seal strength of the tested packages. However, peel strength analysis and distribution testing showed that this reduction in seal strength did not compromise the integrity of 99% of the packages tested. Results showed that the equipment could also detect weak but non‐leaking seals that had potential to lose integrity during transportation and retail handling. The results of this study could be used to determine the capabilities and limitations of a non‐destructive pressure differential bench‐top leak testing device intended for food packaging quality control. Copyright © 2002 John Wiley & Sons, Ltd.     

微小孔尺寸形状的脱模与图像测量

将脱模方法与显微图像处理结合,实现了微小孔内部轮廓的尺寸形状测量.首先采用具有超弹性的乙烯基聚硅氧烷作为制模材料,通过脱模方法将微小孔内部轮廓复制为模型的外部轮廓.然后在显微镜上采集模型的放大图像,利用图像分割、边缘提取、直线检测等图像处理手段,测量出微小孔内部直径随深度的变化曲线.开发出用于测量微小孔尺寸形状的应用软件,利用该软件对脱模法的复制精度进行校验.对于孔口直径在145～155μm的微孔,所制模型在孔口处直径与原始孔口直径的平均绝对值误差为0.9μm.通过脱模方法制作三维型腔模型,得到脱模模型形貌与原始形貌的平均绝对值误差为0.37μm,均方根误差为0.51μm.所提方法融合微米量级的脱模精度和像素级的图像测量精度,可用于微小孔孔径、内部轮廓形状等的测量.     

Modified atmosphere packaging for green chili peppers

Modified atmosphere packages were designed and used for the packaging of green chili peppers. Respiration of green peppers at 10°C was characterized by the closed-system method as a function of O₂ and CO₂ concentrations, and was incorporated into mass balance equations of O₂ and CO₂ gases in order to predict the gas composition inside the package over time. From the prediction of atmospheres inside packages constructed of the available plastic films, three retail packages (110-g peppers) were designed and studied experimentally for their ability to modify the package atmosphere and to retain quality (moisture, ascorbic acid and chlorophyll). Pepper packages using 25 μm low-density polyethylene and 30 μm cast polypropylene could attain modified atmosphere close to the optimal gas concentrations (3% O₂ and 5% CO₂), and therefore provided better quality retention compared with unpackaged controls.     

Temperature dependence of concentrations and mobilities in thin bismuth films

The resistivity, Hall coefficient and magnetoresistance of thin bismuth films were measured at various temperatures (80–300 K) and thicknesses (0.1–3 μm). The mobilities and concentrations of the free electrons and holes were calculated from the experimental data using an anisotropic two-carrier model. Four approaches to the calculation were applied and the results were compared with one another. It was found that the electron and hole concentrations are approximately equal.     

Characteristics of array holes with large aspect ratio in aluminum-based cast alloy

Array holes were obtained by machining methods or nontraditional machining methods, and casting process was rarely used in the preparation of array holes. In this experiment, stainless steel thin rods coated with alcohol group graphite paint were chosen as cores to prepare array holes on aluminum-based cast alloys, and the roughness and roundness of holes were analyzed. The results show that array holes cast with 2?mm pitch of holes, 0.54?mm diameters, and large aspect ratio of 100 were obtained. The roundness and roughness of holes were influenced by consumption of carbon element from surface of hole core and wettability between molten metal and hole core surface; the lower roughness and the better roundness could be acquired under these experimental conditions. And roughness of holes (R_a) was about 6.3?µm, which is close to that obtained by machining, and the value of hole shape factor (K, characterizing the roundness of the hole) was above 0.7; the shape of the hole approached a circular shape.     

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.     

What institutional kitchens require of packages

A theme interview study technique was used to investigate the requirements of institutional kitchens on packages. The interviewees included experts in the food and packaging industries as well as workers in staff restaurants and school dining rooms. Packages containing milk, juice, vegetables and convenience food products were studied. This study shows that the packages did not always function in a satisfactory way. The biggest problem seemed to be the weight of the package and the opening mechanism. The workers are mainly female and therefore 20 kg is too heavy for lifting. It is also important that the package can be disposed of easily. A good package is easy to open and reclose. Reclosing, in particular, proved to be problematic. It is important that the package can be reclosed properly. A problem with packages filled with convenience food is that they are often too full and the food boils over hen heated.     

可加热塑料食品包装中 VOCs 分析

目的分析可加热塑料食品包装中的挥发性有机物(VOCs)。方法以甲醇为溶剂,配制异丙醇、乙酸乙酯、苯、乙酸丁酯、乙苯、间/对二甲苯、邻二甲苯、环己酮的标准溶液,利用顶空/气相色谱-质谱(HS/GC-MS)技术对7种可加热塑料食品包装进行了检测分析,对比加热前后塑料食品包装中VOCs的变化。结果原味酸牛奶包装袋在加热后环己酮的含量明显增加,小酥肉塑料包装盒在加热后异丙醇的含量增加比较明显,粽子塑料包装袋、玉米塑料包装袋、奶茶塑杯、自加热饭盒、微波饭盒在加热前后VOCs含量变化不大。结论这7种包装中的苯类溶剂残留量均超标。     

打孔包装对西兰花品质的影响

分别在2种厚度的PP薄膜(40,50μm)上以一定间距打不同数量的孔(280μm),制得了PP微孔薄膜。将PP微孔薄膜(40μm)制成了自立袋来包装西兰花。通过改变自立袋上微孔的位置,观测袋内气体和西兰花叶绿素含量的变化。结果表明:开孔位置影响袋内O2和CO2气体含量;打孔数量为2个,孔间隔2cm,开孔在西兰花花蕾处时,袋内花蕾处呈低O2和高CO2状态,所包西兰花的叶绿素含量最高,西兰花最新鲜;在环境温度一定的条件下,PP微孔自立袋的厚度、开孔位置、孔径和孔数是影响袋内气体含量的重要因素。     

Reliability of Destructive Leakage Detection Methods for Semirigid Retort Packages

Three different destructive testing methods for package integrity (biotesting, dye penetration and electrical conductance) were compared with each other using intact and leaking retort packages. In biotesting, both vegetative cells of Enterobacter aerogenes and spores of Bacillus subtilis were used as test microbes. The biotest results did not significantly differ from each other, most packages with a 50 μm channel leak through the seal area were contaminated. Biotesting with E. aerogenes was regarded as a more favourable method than testing with spores of B. subtilis since it was easier to perform and gas formation in the packages was a simple indicator for product contamination. The electrolytic test was able to discover most of the leaking packages more reliably than the biotests and the dye penetration test. The dye test had similar sensitivity in identifying leaks to that of the biotests. In conclusion, the microbial integrity of packages should not be estimated only by biotests, even if they are generally regarded as the most severe package integrity test methods.     

PET polymer ablation using excimer laser for nozzle plate application

Abstract

Polyethylene terephthalate (PET) film drilling using a 248 nm excimer laser through photomask projection is presented. The parameter effects of laser fluence, shot number and repetition rate on the processing results are examined. A high quality microhole array with 50 μm thick PET film is fabricated. When the projection process is carried out, the diameter differences in the microhole in the front and back side of PET are observed. This causes a conical shape in the kerf. The formation of this conical shape in terms of the laser process parameters is discussed. The process parameter effects are investigated and characterised to improve the PET microhole laser machining quality.     

Plasmonic Color Filters for CMOS Image Sensor Applications

We report on the optical properties of plasmonic hole arrays as they apply to requirements for plasmonic color filters designed for state-of-the-art Si CMOS image sensors. The hole arrays are composed of hexagonally packed subwavelength sized holes on a 150 nm Al film designed to operate at the primary colors of red, green, and blue. Hole array plasmonic filters show peak transmission in the 40-50% range for large (>5 × 5 μm(2)) size filters and maintain their filtering function for pixel sizes as small as ～1 × 1 μm(2), albeit at a cost in transmission efficiency. Hole array filters are found to robust with respect to spatial crosstalk between pixel within our detection limit and preserve their filtering function in arrays containing random defects. Analysis of hole array filter transmittance and crosstalk suggests that nearest neighbor hole-hole interactions rather than long-range interactions play the dominant role in the transmission properties of plasmonic hole array filters. We verify this via a simple nearest neighbor model that correctly predicts the hole array transmission efficiency as a function of the number of holes.