Detecting leaks in modified atmosphere packaging E Hurme, VTT Biotechnology, Finland 13.1 Introduction Package integrity is an essential requirement for maintaining the high quality of for example, sterilised foods and modified atmosphere packaged foods. The increasing focus on quality assurance is putting demands on verification of food package integrity. The foremost noticeable package integrity problem is probably leaking seals, particularly with flexible plastic packages which are more prone to mechanical damage than traditional rigid metal packages. A non- destructive leak test device allowing evaluation of every container produced is therefore. of interest to food manufacturers Non-destructive package leak testing equipment detects defective packages immediately in the packaging line. This can be considered as an integral part of packaging process control. The most effective way to detect a package leakage, non-destructively, throughout the whole distribution chain from the manufacturer to the consumer is a leak indicator permanently attached to the package. One key element in selecting a proper leak test device and leak indicator is knowledge of the leakages, which are critical to the product shelf-life This chapter reviews the integrity requirements of flexible food package on-destructive package leak test methods, and intelligent leak indicators for modified atmosphere packages 13.2 Leakage, product safety and quality Before the selection of leak-testing methods for different packages can be made it is essential to have information concerning the required integrity of different
13.1 Introduction Package integrity is an essential requirement for maintaining the high quality of, for example, sterilised foods and modified atmosphere packaged foods. The increasing focus on quality assurance is putting demands on verification of food package integrity. The foremost noticeable package integrity problem is probably leaking seals, particularly with flexible plastic packages which are more prone to mechanical damage than traditional rigid metal packages. A nondestructive leak test device allowing evaluation of every container produced is, therefore, of interest to food manufacturers. Non-destructive package leak testing equipment detects defective packages immediately in the packaging line. This can be considered as an integral part of packaging process control. The most effective way to detect a package leakage, non-destructively, throughout the whole distribution chain from the manufacturer to the consumer is a leak indicator permanently attached to the package. One key element in selecting a proper leak test device and leak indicator is knowledge of the leakages, which are critical to the product shelf-life. This chapter reviews the integrity requirements of flexible food packages, non-destructive package leak test methods, and intelligent leak indicators for modified atmosphere packages. 13.2 Leakage, product safety and quality Before the selection of leak-testing methods for different packages can be made, it is essential to have information concerning the required integrity of different 13 Detecting leaks in modified atmosphere packaging E. Hurme, VTT Biotechnology, Finland
Detecting leaks in modified atmosphere packaging 277 Table 13.1 Deterioration factors related to critical channel leakages in different packaged foods epic and Ready-to-eat Baked goods Dried goods sterilised meal microbial on, oxidation oxidation moisture 1,3591230-50m chang >13 diameter in package package types and products. That is, how big a leakage can there be without the packed product deteriorating microbiologically or chemically before the use-by date, and how small a leakage should the leak testing method detect (Table In many studies leakages of around 10 um in diameter have been demonstrated. under strict conditions. to cause microbial contamination in model packages- and in commercially processed and packaged aseptic packages ,", The critical leakage size causing accelerated quality deterioration in gas-flushed modified atmosphere packages (MAP)may vary considerabl ly between different products and packaging methods. Small leakages(hole diameter 169um, hole length 3mm)in gas packages have even been reported to retain the quality of packed minced meat steaks better than in intact packages. Other recent studies have, on the other hand, revealed accelerated quality deterioration of raw marinated chicken breast and raw rainbow trout and pizza in gas packages with leakages as small as 30um and 55um(hole length 3mm), respectively. Table 13.1 summarises the most important deterioration factors of different packaged foods and studies concerning critical leakages 13.3 Package leak detection during processing 13.3.1 Methods in use package and seal integrity is widely verified using destructive manual ods, such as a biotest, electrolytic test, dye penetration test and bubble test The major drawbacks of destructive test methods are that it is not possible to check every package produced, and the tests are often laborious. An automated, iable, 100% in-line non-destructive leak test machine allowing testing of every container produced would, therefore, be of interest to companies. This kind of package testing would serve as an immediate process control tool resulting in an overall cost reduction in terms of a reduced number of packages
package types and products. That is, how big a leakage can there be without the packed product deteriorating microbiologically or chemically before the use-by date, and how small a leakage should the leak testing method detect (Table 13.1). In many studies leakages of around 10 m in diameter have been demonstrated, under strict conditions, to cause microbial contamination in model packages1,2 and in commercially processed and packaged aseptic packages. 3,4,5 The critical leakage size causing accelerated quality deterioration in gas-flushed modified atmosphere packages (MAP) may, however, vary considerably between different products and packaging methods. Small leakages (hole diameter 130 m13 diameter in package Detecting leaks in modified atmosphere packaging 277
278 Novel food packaging techniques Table 13.2 Commercial methods for non-destructive food package leakage detection Test stimulus Test response Application External pressure Package movement Packages with headspace Pressure decay* External vacuum Package movement Pressure decay* Tracer gas(H2. CO2, He, SF6 Internal pressure queerer movement Packages with headspace Package movement* Internal vacuum kage moveme All packages Machine vision Image change Foil packages On-line application available. ost both in production and in destructive testing. Also, complaints and returns from retailers and consumers relating to leaky packages and deteriorated products would be diminished Much interest has concentrated on plastic food packages to define thei integrity requirements, .2.4, 8. 4, I5 to research and develop new non-destructive test methods, 6-9 and to evaluate the reliability of commercial non-destructive test methods. 4 In-line non-destructive test equipment should meet demands such as: reliable identification and rejection of all the defective packages produced; fast leak detection; non-damaging to the product; easy to use and maintain; and reasonable supply and operating costs Most non-destructive leak inspection systems for flexible and semi-rigid packages are based on a stimulus response technique: the stimulus to the package can be, for example, ultrasound,pressure, tracer gas like helium, carbon dioxide or hydrogen- and the response can be, for example, sound/beam reflection, package movement, pressure change, or tracer gas detection(Table 13.2). In recent years, numerous new patents suitable for non-destructive food or medical package integrity testing have been published Although tracer gas detection is a very sensitive method, detection of pressure differential is perhaps currently the most popular method employed for flexible and semi-rigid packages with a headspace. Commercial pressure differential methods are typically based either(i)on detection of an external rise or fall in pressure in a test chamber created outside the package with compressed air or a vacuum pump, respectively, or(ii) on detection of an internal fall in pressure created inside the package either mechanically or by heat. Evaluation studies of commercial automated non-destructive leak detectors based on detection pressure differentials revealed that these test methods-although used in industry were not capable of reliably detecting leakages that proven to be penetrable by harmful microbes
lost both in production and in destructive testing. Also, complaints and returns from retailers and consumers relating to leaky packages and deteriorated products would be diminished. Much interest has concentrated on plastic food packages to define their integrity requirements,1,2,4,8,14,15 to research and develop new non-destructive test methods, 16-19 and to evaluate the reliability of commercial non-destructive test methods. 15,20 In-line non-destructive test equipment should meet demands such as: reliable identification and rejection of all the defective packages produced; fast leak detection; non-damaging to the product; easy to use and maintain; and reasonable supply and operating costs. Most non-destructive leak inspection systems for flexible and semi-rigid packages are based on a stimulus response technique: the stimulus to the package can be, for example, ultrasound,18 pressure,22 tracer gas like helium,23 carbon dioxide16 or hydrogen21 and the response can be, for example, sound/beam reflection, package movement, pressure change, or tracer gas detection (Table 13.2). In recent years, numerous new patents suitable for non-destructive food or medical package integrity testing have been published. Although tracer gas detection is a very sensitive method, detection of pressure differential is perhaps currently the most popular method employed for flexible and semi-rigid packages with a headspace. Commercial pressure differential methods are typically based either (i) on detection of an external rise or fall in pressure in a test chamber created outside the package with compressed air or a vacuum pump, respectively, or (ii) on detection of an internal fall in pressure created inside the package either mechanically or by heat. Evaluation studies of commercial automated non-destructive leak detectors based on detection pressure differentials revealed that these test methods – although much used in industry – were not capable of reliably detecting leakages that were proven to be penetrable by harmful microbes.20,22,23 Table 13.2 Commercial methods for non-destructive food package leakage detection Test stimulus Test response Application External pressure Package movement* Packages with headspace Pressure decay* External vacuum Package movement* Packages with headspace Pressure decay* Tracer gas (H2, CO2, He, SF6) Internal pressure Squeezer movement* Packages with headspace Package movement* Internal vacuum Package movement* All packages Machine vision Image change* Foil packages * On-line application available. 278 Novel food packaging techniques
Detecting leaks in modified atmosphere packaging 279 13.3.2 Novel tracer gas system for in-line application Tracer ak detection methods are very sensitive, and the most commonly used gas has been helium. Another possibility is to use the more economical carbon dioxide as a tracer gas. Carbon dioxide is often routinely used as protective packaging gas in food packages, which eliminates the need for the special addition of tracer gas in the package. However, introduction of automatic in-line leak detectors based on helium or carbon dioxide tracer gases has not been successful. The reasons for this have possibly been the relatively high operating and supply costs of the helium method, or the unfavourable physical characteristics of the carbon dioxide method A novel leak-detection system has recently developed at VTT using hydrogen (H2)as a tracer gas. The leak tester utilising H2 and a very sensitive hydrogen detector is very effective and fast and is especially suitable for MAP For example, at least 30um diameter holes in a gas-flushed package have been demonstrated to be reliably detected within one second. Using this method, a package containing H2 tracer gas is positioned in a specially designed test chamber. A vacuum pressure is then drawn into the test chamber and the package expands due to the increased pressure differential between the package walls. Trace amounts of H2 are then forced out of leaking packages through a pipe in which a H2 sensor is positioned towards the gas flow. The sensor connected to the H2 detector reacts to the H2, and immediately gives an electrical signal to the H, detector H2 has many characteristics advantageous to its use as a tracer gas in leak detection. First of all, it is a colourless, odourless, tasteless and non-toxic gas at atmospheric temperatures and pressures. A non-flammable concentration (5% in air) of hydrogen is sufficient for sensitive leak detection evertheless, the tracer gas concentration in the package heads background concentration of H2 in air, only 0. 5ppm, enables sensitive leak detection. That is, the minimum detection limit of H2 escaping from a defective package is very low. In comparison, the carbon dioxide and helium concentrations in air are 300 and 5 ppm, respectively. Hydrogen is also the lightest of all gases(molecular weight: H2 2.0, He 4.0, CO2 44.0, air 29. 0g/ mol) thus reducing the risk of background gas contamination in the leak test area. For example, carbon dioxide as a heavier gas than air may accumulate in the leak test area creating a risk of false readings 13.4 Package leak indicators during distribution The modified atmosphere package for non-respiring food typically has a low(0 2%)oxygen(O2)concentration and a high(20-80%)carbon dioxide(co2) concentration. Hence a leak means a considerable increase in O, concentration and a decrease in CO2 concentration. If the package leaks, microbial growth
13.3.2 Novel tracer gas system for in-line application Tracer gas leak detection methods are very sensitive, and the most commonly used gas has been helium. Another possibility is to use the more economical carbon dioxide as a tracer gas. Carbon dioxide is often routinely used as a protective packaging gas in food packages, which eliminates the need for the special addition of tracer gas in the package. However, introduction of automatic in-line leak detectors based on helium or carbon dioxide tracer gases has not been successful. The reasons for this have possibly been the relatively high operating and supply costs of the helium method, or the unfavourable physical characteristics of the carbon dioxide method. A novel leak-detection system has recently developed at VTT using hydrogen (H2) as a tracer gas.21,24 The leak tester utilising H2 and a very sensitive hydrogen detector is very effective and fast and is especially suitable for MAP. For example, at least 30m diameter holes in a gas-flushed package have been demonstrated to be reliably detected within one second.21 Using this method, a package containing H2 tracer gas is positioned in a specially designed test chamber. A vacuum pressure is then drawn into the test chamber and the package expands due to the increased pressure differential between the package walls. Trace amounts of H2 are then forced out of leaking packages through a pipe in which a H2 sensor is positioned towards the gas flow. The sensor connected to the H2 detector reacts to the H2, and immediately gives an electrical signal to the H2 detector. H2 has many characteristics advantageous to its use as a tracer gas in leak detection. First of all, it is a colourless, odourless, tasteless and non-toxic gas at atmospheric temperatures and pressures. A non-flammable concentration (<5% in air) of hydrogen is sufficient for sensitive leak detection. Nevertheless, the tracer gas concentration in the package headspace is proportional to the leak detection sensitivity and speed; even concentrations as low as 0.5% can be used to detect relatively small leakages. The low background concentration of H2 in air, only 0.5ppm, enables sensitive leak detection. That is, the minimum detection limit of H2 escaping from a defective package is very low. In comparison, the carbon dioxide and helium concentrations in air are 300 and 5 ppm, respectively. Hydrogen is also the lightest of all gases (molecular weight: H2 2.0, He 4.0, CO2 44.0, air 29.0g/ mol) thus reducing the risk of background gas contamination in the leak test area. For example, carbon dioxide as a heavier gas than air may accumulate in the leak test area creating a risk of false readings. 13.4 Package leak indicators during distribution The modified atmosphere package for non-respiring food typically has a low (0– 2%) oxygen (O2) concentration and a high (20–80%) carbon dioxide (CO2) concentration. Hence, a leak means a considerable increase in O2 concentration and a decrease in CO2 concentration. If the package leaks, microbial growth is Detecting leaks in modified atmosphere packaging 279
280 Novel food packaging techniques likely to take place. This means that CO2 may in some cases accumulate in package. In the worst case, the CO2 concentration will remain high despite leakage and microbial growth. Thus, the leak indicators for modified atmosphere packages should rely on the detection of oxygen rather than on the detection of 13. 4.1 Visual oxygen indicators At present, the main application of commercially available O2-sensitive package indicators is to ensure the proper functioning of oxygen absorption; companies that also deal with O2 absorbers have developed the indicators. For example, Mitsubishi Gas Chemical Company in Japan has greatly contributed to the development of O2 absorbers and was the first to commercialise O2-absorbing sachets under the trade name 'Ageless.The"Ageless-Eyesachets containing an O, indicator tablet have been designed to confirm that the 'Ageless absorbers are functioning properly. The manufacturer claims that indicator tablet turns from blue into pink within 2-3 hours after Oz has reached a zero concentration at 25C and into blue again in about five minutes when it is in contact with O2. Also some other Japanese companies like Toppan Printing have been active in developing oxygen indicators A typical visual O2 indicator consists of a redox dye, i. e, a reducing compound and an alkaline compound. In addition to these main component compounds such as a solvent(typically water and/or alcohol)and bulking agent (e.g. zeolite, silica gel, cellulose materials, polymers)are added to the indicator The indicator can be formulated as a tablet26-27 or a printed layer28-30 or it can be laminated in a polymer film. The redox dyes of the indicators are oxidised by O2 and a colour change can be observed. The most common dye used in the indicators is methylene blue, which is typically white in the reduced state and blue in the oxidised state. Other redox dyes used in O2 indicators are 2,6- dichloroindophenol and N, N, N, N-tetramethyl-p-phenylenediamine 3A reducing compound is added to the O2 indicator to reduce the dye and to keep it in the reduced state during the packaging process. Common reducing compounds for O2 indicators are reducing sugars, but inorganic salts as well as reduction by irradiation have also been used. An alkaline compound is added to the indicator to maintain the ph on the alkaline side and thus prevent too rapid an oxidation reaction of the dye 34-35 Inorganic compounds, such as sodium have typically been used for this purpose. ,30-ide and magnesium hydroxide hydroxide, potassium hydroxide, calcium hydrox a different approach to constructing a visual O2 indicator was introduced by Krumhar Karel- who developed a two-step colour reaction. In the first reaction step O2-sensitive material is oxidised and the formation of an acid or peroxide occurs. These components will cause a colour change in the specific colorant included in the system. Oxidative enzyme-based oxygen indicators ave been described by ahvenainen et al. and gardiol et a
likely to take place. This means that CO2 may in some cases accumulate in package. In the worst case, the CO2 concentration will remain high despite leakage and microbial growth. Thus, the leak indicators for modified atmosphere packages should rely on the detection of oxygen rather than on the detection of CO2. 13.4.1 Visual oxygen indicators At present, the main application of commercially available O2-sensitive package indicators is to ensure the proper functioning of oxygen absorption; companies that also deal with O2 absorbers have developed the indicators. For example, Mitsubishi Gas Chemical Company in Japan has greatly contributed to the development of O2 absorbers and was the first to commercialise O2-absorbing sachets under the trade name ‘Ageless’. 25 The ‘Ageless-Eye’ sachets containing an O2 indicator tablet have been designed to confirm that the ‘Ageless’ absorbers are functioning properly. The manufacturer claims that indicator tablet turns from blue into pink within 2–3 hours after O2 has reached a zero concentration at 25ºC and into blue again in about five minutes when it is in contact with O2. Also some other Japanese companies like Toppan Printing have been active in developing oxygen indicators. A typical visual O2 indicator consists of a redox dye, i.e., a reducing compound and an alkaline compound. In addition to these main components, compounds such as a solvent (typically water and/or alcohol) and bulking agent (e.g. zeolite, silica gel, cellulose materials, polymers) are added to the indicator. The indicator can be formulated as a tablet26–27 or a printed layer28–30 or it can be laminated in a polymer film.31 The redox dyes of the indicators are oxidised by O2 and a colour change can be observed. The most common dye used in the indicators is methylene blue, which is typically white in the reduced state and blue in the oxidised state. Other redox dyes used in O2 indicators are 2,6- dichloroindophenol 32 and N,N,N0 ,N0 -tetramethyl-p-phenylenediamine. 33 A reducing compound is added to the O2 indicator to reduce the dye and to keep it in the reduced state during the packaging process. Common reducing compounds for O2 indicators are reducing sugars, but inorganic salts as well as reduction by irradiation have also been used. An alkaline compound is added to the indicator to maintain the pH on the alkaline side and thus prevent too rapid an oxidation reaction of the dye.34–35 Inorganic compounds, such as sodium hydroxide, potassium hydroxide, calcium hydroxide and magnesium hydroxide, have typically been used for this purpose.27,30 A different approach to constructing a visual O2 indicator was introduced by Krumhar & Karel29 who developed a two-step colour reaction. In the first reaction step O2-sensitive material is oxidised and the formation of an acid or peroxide occurs. These components will cause a colour change in the specific colorant included in the system. Oxidative enzyme-based oxygen indicators have been described by Ahvenainen et al.36 and Gardiol et al.37–38 280 Novel food packaging techniques
Detecting leaks in modified atmosphere packaging 281 13.4.2 Invisible oxygen indicators In addition to the purely visual O2 indicators, some other systems can also be considered as indicators even if external equipment is needed. These systems possess, however, an internal indicator attached to the package and can be interpreted non-destructively. The concept of luminescent dyes quenched by O2 as indicators for food packages was preliminarily introduced by Reininger et al.' This optical method can be used for quantitative measurement of O concentration in a non-destructive manner. Maurer" suggests a system using the conversion of o, to ozone with the aid of uv radiation or an electric field. the presence of ozone is shown with a potassium iodide/starch indicator strip A more recent approach is an optical oxygen-sensing method developed at TNO. The measurement principle is based on the fluorescence quenching of a metal-organic fluorescent dye, which is immobilised in a hydrofobic polymer The dye is excited by an excitation pulse, after which the dye emits fluorescent light proportional to O2 concentration. The dye is claimed to be very sensitive to O2 and the measurement can take less than one second. The system can be used for measuring O2 in gas and dissolved in water. In principle, this method could be used also for in-line application. However, these measurements need time after packaging to allow oxygen to enter into the package through a 13.4.3 The applicability and restrictions of oxygen indicators In MAPs the high sensitivity of oxygen indicators is not advantageous as the sensitive indicator might also react with the residual O, which is often entrapped in the modified-atmosphere package during the packaging procedure (typically <1.0%). Extreme sensitivity also complicates handling of the indicator and anaerobic conditions are required during the preparation of the indicator and the packaging procedure. As the O2 concentration required for the colour change of most indicators is around 0. 1% they cannot be applied to the leak indication of MAPs as such. It has been claimed that the colour change of o, indicators used in MAPs containing acidic CO2 gas is not definite enough Many of the patented O2 indicators are reversible in their colour change and change colour according to the prevailing O2 concentration-,However, the rever sibility is undesirable if the indicator is used for leakage control since the O2 entering the package through the leak will be consumed during the microbial growth that is likely to follow the loss of the package integrity. In the worst case, the indicator colour will be the same as for intact packages, even if the product has been spoiled A visual O2 indicator designed specifically for leak detection of MAPs has been developed at VTT. This indicator, which is based on an oxygen-sensitive dye, is suitable for the quality control of modified-atmosphere-packed products and it contains, in addition to the oxygen-sensitive component, an oxygen-absorbing component, and can hence prolong the product's shelf-life This leak indicator does not react with the ual O2 entrapped in the
13.4.2 Invisible oxygen indicators In addition to the purely visual O2 indicators, some other systems can also be considered as indicators even if external equipment is needed. These systems possess, however, an internal indicator attached to the package and can be interpreted non-destructively. The concept of luminescent dyes quenched by O2 as indicators for food packages was preliminarily introduced by Reininger et al.39 This optical method can be used for quantitative measurement of O2 concentration in a non-destructive manner. Maurer40 suggests a system using the conversion of O2 to ozone with the aid of UV radiation or an electric field. The presence of ozone is shown with a potassium iodide/starch indicator strip. A more recent approach is an optical oxygen-sensing method developed at TNO. The measurement principle is based on the fluorescence quenching of a metal-organic fluorescent dye, which is immobilised in a hydrofobic polymer. The dye is excited by an excitation pulse, after which the dye emits fluorescent light proportional to O2 concentration. The dye is claimed to be very sensitive to O2 and the measurement can take less than one second.41 The system can be used for measuring O2 in gas and dissolved in water. In principle, this method could be used also for in-line application. However, these measurements need time after packaging to allow oxygen to enter into the package through a leakage.42 13.4.3 The applicability and restrictions of oxygen indicators In MAPs the high sensitivity of oxygen indicators is not advantageous as the sensitive indicator might also react with the residual O2, which is often entrapped in the modified-atmosphere package during the packaging procedure (typically <1.0%). Extreme sensitivity also complicates handling of the indicator and anaerobic conditions are required during the preparation of the indicator and the packaging procedure. As the O2 concentration required for the colour change of most indicators is around 0.1% they cannot be applied to the leak indication of MAPs as such. It has been claimed that the colour change of O2 indicators used in MAPs containing acidic CO2 gas is not definite enough.34,43–44 Many of the patented O2 indicators are reversible in their colour change and change colour according to the prevailing O2 concentration27,45 However, the reversibility is undesirable if the indicator is used for leakage control since the O2 entering the package through the leak will be consumed during the microbial growth that is likely to follow the loss of the package integrity. In the worst case, the indicator colour will be the same as for intact packages, even if the product has been spoiled. A visual O2 indicator designed specifically for leak detection of MAPs has been developed at VTT.34 This indicator, which is based on an oxygen-sensitive dye, is suitable for the quality control of modified-atmosphere-packed products13 and it contains, in addition to the oxygen-sensitive component, an oxygen-absorbing component, and can hence prolong the product’s shelf-life. This leak indicator does not react with the residual O2 entrapped in the Detecting leaks in modified atmosphere packaging 281
282 Novel food packaging techniques modified-atmosphere package because the Oz-absorbing component with adjusted capacity for the residual O2 is included in the indicator and, moreover the indicator is included in a film composition which protects against oxidation of the indicator during packaging 13.4.4 Carbon dioxide indicators CO2 is widely used as a protective gas in modified-atmosphere packaging During the first 12 days after the packaging procedure CO2 is dissolved into the product and its concentration in the head-space is decreased, the final concentration being even as low as half of the original. After this period (1-2 days)a considerable decrease in CO2 concentration is an evident sign of leakage in a package. However, CO2 is also produced in microbial metabolism and its accumulation in a package headspace can be considered to be a sign of microbial growth. A leak in a package( decrease in the CO2)is often followed by microbial growth (increase in the CO2)and, in the worst case, the CO2 will remain constant even in the case of leakage and microbial spoilage. For these two reasons, CO2 indicators as leak indicators appear not to be as reliable as O2 indicators In their patent Balderson Whitwood"o describe a reversible CO2 indicator suitable for modified atmosphere packages. The indicator consists of, for example, five indicator strips. The strips contain CO2-sensitive indicator material consisting, for example, of an indicator anion and a lipophilic organic quaternary cation. +/The colour change of each strip has been designed to take place when the CO2 concentration is below a certain limit(e.g. 25%, 20%, 15%, 10% or 5%). The concentration of CO2 is indicated by a change of colour in one or more of the strips. Sealed Air Ltd has produced a visible CO2 indicator for MAPs 13.4.5 Safety aspects A self-evident requirement for internal indicators placed in the package headspace is their absolute safety. The legislative aspects are discussed in Chapters 19 and 22. 13.5 Future trends Package integrity is an essential requirement for maintaining the high quality of e.g., sterilised and modified atmosphere packaged foods. The increasing focus on quality assurance is putting demands on verification of food package and seal grity. On the other hand, much effort is and will also be put into the development of new materials and packaging systems with minimised risk of cage failur Non-destructive package leak detection systems installed in-line are not yet very widely used, mainly because of high costs and lack of reliability/sensitivity
modified-atmosphere package because the O2-absorbing component with adjusted capacity for the residual O2 is included in the indicator and, moreover, the indicator is included in a film composition which protects against oxidation of the indicator during packaging. 13.4.4 Carbon dioxide indicators CO2 is widely used as a protective gas in modified-atmosphere packaging. During the first 12 days after the packaging procedure CO2 is dissolved into the product and its concentration in the head-space is decreased, the final concentration being even as low as half of the original. After this period (1–2 days) a considerable decrease in CO2 concentration is an evident sign of leakage in a package. However, CO2 is also produced in microbial metabolism and its accumulation in a package headspace can be considered to be a sign of microbial growth. A leak in a package (decrease in the CO2) is often followed by microbial growth (increase in the CO2) and, in the worst case, the CO2 will remain constant even in the case of leakage and microbial spoilage. For these two reasons, CO2 indicators as leak indicators appear not to be as reliable as O2 indicators. In their patent Balderson & Whitwood44–46 describe a reversible CO2 indicator suitable for modified atmosphere packages. The indicator consists of, for example, five indicator strips. The strips contain CO2-sensitive indicator material consisting, for example, of an indicator anion and a lipophilic organic quaternary cation.47 The colour change of each strip has been designed to take place when the CO2 concentration is below a certain limit (e.g. 25%, 20%, 15%, 10% or 5%). The concentration of CO2 is indicated by a change of colour in one or more of the strips. Sealed Air Ltd has produced a visible CO2 indicator for MAPs. 13.4.5 Safety aspects A self-evident requirement for internal indicators placed in the package headspace is their absolute safety. The legislative aspects are discussed in Chapters 19 and 22. 13.5 Future trends Package integrity is an essential requirement for maintaining the high quality of, e.g., sterilised and modified atmosphere packaged foods. The increasing focus on quality assurance is putting demands on verification of food package and seal integrity. On the other hand, much effort is and will also be put into the development of new materials and packaging systems with minimised risk of package failures. Non-destructive package leak detection systems installed in-line are not yet very widely used, mainly because of high costs and lack of reliability/sensitivity 282 Novel food packaging techniques
Detecting leaks in modified atmosphere packaging 283 to find all defective packages. New reliable and cost-effective systems are needed. One candidate for this could be the use of hydrogen as a tracer gas Another possibility could be oxygen indicator labels or dyes printed onto packaging material and read automatically at a distance lay, application of intelligent package leak-indicating systems in Europe has been limited to some time-temperature indicators. However, some food saucers are increasingly seeking extra merchandising and safety features Intelligent leak indicators marketed, e.g., as 'premium quality labels' can be seen to give added value to the product/brand image. The visible indicators are ideal in many cases, however, in the future it can be expected that an intelligent package can contain more complex invisible messages that can be read at a distance. A label could be introduced as a chip but advances in ink technology might enable the use of printed circuits as well. The security tags and radio frequency identity/tracebility tags are the first examples of electronic label Another approach for the future is the development of different optically read Development of these ' next generation' intelligent labels/printing systems is very challenging, e.g., in terms of cost demands, effectiveness and logistics Standardisation will undoubtedly be one of the key issues when new systems are pushed onto the market. The basic requirement for success in making intelligent systems work in real life is collaboration between research institutes, authorities, and companies from product manufacturers and raw material supplier to retailer 13.6 References 1. CHEN, C, HARTE, B, LAL, C, PETSKA, J. and HENYON, D. Assessment of package integrity using a spray cabinet technique. J. Food Prot. 1991, 54 643-7 2. KELLER, S W, MARCY, J.E., BLACKISTONE, B.A., LACY, G.H., HACKNEY, C.R. and CARTER, W.H. Bioaerosol exposure method for package integrity testing.J. Food Prot. 1996, 59: 768-71 3. AHVENAINEN, R, MATTILA-SANDHOLM, T, AXELSON, L and WIRTANEN, G The effect of microhole size and foodstuff on the microbial integrity of aseptic plastic cups. Pack. Techn. Sci. 1992, 5: 101-7 4. BLACKISTONE, B.A., KELLER, S.W., MARCY, J.E., LACY, G.H., HACKNEY, C.R. and CARTER, W.H. Contamination of flexible pouches challenged by immersion biotesting J. Food Prot. 1996. 59: 764-7 5. HURME. E. WIRTANEN. G. AXELSON-LARSSON. L. PAChERO. A. and AHVENAINEN, R. Penetration of bacteria through microholes in semirigid aseptic and retort packages. J. Food Prot. 1997, 60: 520-5 6. EILAMO, M, AHVENAINEN, R, HURME, E, HEINIO, R.L. and MATTILA- SANDHOLM, T. The effect of package leakage on the shelf-life of modified atmosphere packed minced meat steaks and its detection Lebensm.-liss Techi.1995.28:62-71
to find all defective packages. New reliable and cost-effective systems are needed. One candidate for this could be the use of hydrogen as a tracer gas. Another possibility could be oxygen indicator labels or dyes printed onto packaging material and read automatically at a distance. Today, application of intelligent package leak-indicating systems in Europe has been limited to some time-temperature indicators. However, some food producers are increasingly seeking extra merchandising and safety features. Intelligent leak indicators marketed, e.g., as ‘premium quality labels’ can be seen to give added value to the product/brand image. The visible indicators are ideal in many cases, however, in the future it can be expected that an intelligent package can contain more complex invisible messages that can be read at a distance. A label could be introduced as a chip but advances in ink technology might enable the use of printed circuits as well. The security tags and radio frequency identity/tracebility tags are the first examples of electronic labelling. Another approach for the future is the development of different optically read systems. Development of these ‘next generation’ intelligent labels/printing systems is very challenging, e.g., in terms of cost demands, effectiveness and logistics. Standardisation will undoubtedly be one of the key issues when new systems are pushed onto the market. The basic requirement for success in making intelligent systems work in real life is collaboration between research institutes, authorities, and companies from product manufacturers and raw material supplier to retailer. 13.6 References 1. CHEN, C., HARTE, B., LAI, C., PETSKA, J. and HENYON, D. Assessment of package integrity using a spray cabinet technique. J. Food Prot. 1991, 54: 643–7. 2. KELLER, S.W., MARCY, J.E., BLACKISTONE, B.A., LACY, G.H., HACKNEY, C.R. and CARTER, W.H. Bioaerosol exposure method for package integrity testing. J. Food Prot. 1996, 59: 768–71. 3. AHVENAINEN, R., MATTILA-SANDHOLM, T., AXELSON, L. and WIRTANEN, G. The effect of microhole size and foodstuff on the microbial integrity of aseptic plastic cups. Pack. Techn. Sci. 1992, 5: 101–7. 4. BLACKISTONE, B.A., KELLER, S.W., MARCY, J.E., LACY, G.H., HACKNEY, C.R. and CARTER., W.H. Contamination of flexible pouches challenged by immersion biotesting. J. Food Prot. 1996, 59: 764–7. 5. HURME, E., WIRTANEN, G., AXELSON-LARSSON, L., PACHERO, A. and AHVENAINEN, R.. Penetration of bacteria through microholes in semirigid aseptic and retort packages. J. Food Prot. 1997, 60: 520–5. 6. EILAMO, M., AHVENAINEN, R., HURME, E., HEINIO¨ , R-L. and MATTILASANDHOLM, T. The effect of package leakage on the shelf-life of modified atmosphere packed minced meat steaks and its detection. Lebensm.-Wiss. - Techn. 1995, 28: 62–71. Detecting leaks in modified atmosphere packaging 283
284 Novel food packaging 7. RANDELL, K, AHVENAINEN, R, LATVA-KALA, K, HURME, E, MATTILA- SANDHOLM, T and HYVONEN, L Modified atmosphere-packed marinated chicken breast and rainbow trout quality as affected by package leakage. J. Food Sc.1995,60:.667-72,684 8. AHVENAINEN, R, EILAMO, M and HURME, E. Detection of improper sealing and quality deterioration of MA-packed pizza by a colour indicator. Food Control1997,8:177-84 9. GILCHRIST. J.E. SHAH. D.B. RADLE D.C. and DICKERSoN. R w. Leak detection in flexible retort pouches. J. Food Prot. 1989, 52: 412-15 LAMPL,RA. Retort pouch: the development of a basic packaging concept in oday's high technology era. J. Food Proc. Eng. 1980, 4: 1-18 11. MARCY, J.E. Integrity testing and biotest procedures for heat-sealed containers. In:(Blackiestone, B.A. and Harper, C L, eds), Plastic Package Integrity Testing -Assuring Seal Quality Institute of Packaging Professionals, Herndon, Virginia. pp. 35-48. 1995 12. ROSE, D. Risk factors associated with post process contamination of hear sealed semi-rigid packaging. Techn. Mem. No. 708. CCFRA, Chipping Campden, Gloucestershire, 1994 13. AHVENAINEN, R, HURME, E, RANDELL, K. and EILAMO, M. The effect of akage on the quality of gas-packed foodstuffs and the leak detection VTT Research Notes 1683, Espoo, Finland, 1995 14. AXELSON, L, CAVLIN, S and NORDSTROM, J. Aseptic integrity and microhole determination of packages by electrolytic conductance measurement Pack. Techn. Sci. 1990. 3: 141-62 15. HURME. E, WIRTANEN. G, AXELSON-LARSSON, L. and AhvENAInEN, R Testing of reliability of non-destructive pressure differential package leakage testers with semirigid aseptic cups. Food Control. 1998, 9: 49-55 16. JENSEN, P. Testing of package integrity based on CO2 as a trace gas. Proc APRI Symp. Reims, 9-12 October 1994, 9 p 17. SAFVI A, MEERBAUM, M, MORRIS, S. HARPER, C and o'BRIen w. Acoustic 18 ging of defects in flexible food packages. J. Food Prot.1997,60: 309- SONG,Y,LEE, H. and YAM, K. Feasibility of using a non-destructive ultrasonic technique for detecting defective seals. Pack. Techn. Sci. 1993 6:37-42 19. YAM, K.L. Pressure differential techniques for package integrity inspection In (Blakistone, B.A. and Harper, C.L. eds) Plastic Package Integrity Testing assuring Seal Quality, Institute of Packaging Professionals, Herndon, VA, pp. 137-46, 1995 20. HURME. E. WIRTANEN. G. AXELSON-LARSSON. L. and ahvenainen Reliability of non-destructive pressure differential package leakage testers using semirigid retort trays. Food Sci. Techn. 1998, 31: 461-6 21. HURME E. and AHVENAINEN R. 1998. A nondestructive leak detection method for flexible food packages using hydrogen as a tracer gas. J. Food Prot.1998.61:11659
7. RANDELL, K., AHVENAINEN, R., LATVA-KALA, K., HURME, E., MATTILASANDHOLM, T. and HYVO¨ NEN, L. Modified atmosphere-packed marinated chicken breast and rainbow trout quality as affected by package leakage. J. Food Sci. 1995, 60: 667–72, 684. 8. AHVENAINEN, R., EILAMO, M. and HURME, E. Detection of improper sealing and quality deterioration of MA-packed pizza by a colour indicator. Food Control 1997, 8: 177–84. 9. GILCHRIST, J.E., SHAH, D.B., RADLE, D.C. and DICKERSON., R.W. Leak detection in flexible retort pouches. J. Food Prot. 1989, 52: 412–15. 10. LAMPI, R.A. Retort pouch: the development of a basic packaging concept in today’s high technology era. J. Food Proc. Eng. 1980, 4: 1–18. 11. MARCY, J.E. Integrity testing and biotest procedures for heat-sealed containers. In: (Blackiestone, B.A. and Harper, C.L., eds), Plastic Package Integrity Testing – Assuring Seal Quality. Institute of Packaging Professionals, Herndon, Virginia. pp. 35–48. 1995. 12. ROSE, D. Risk factors associated with post process contamination of heat sealed semi-rigid packaging. Techn. Mem. No. 708. CCFRA, Chipping Campden, Gloucestershire, 1994. 13. AHVENAINEN, R., HURME, E., RANDELL, K. and EILAMO, M. The effect of leakage on the quality of gas-packed foodstuffs and the leak detection. VTT Research Notes 1683, Espoo, Finland, 1995. 14. AXELSON, L., CAVLIN, S. and NORDSTRO¨ M, J. Aseptic integrity and microhole determination of packages by electrolytic conductance measurement. Pack. Techn. Sci. 1990, 3: 141–62. 15. HURME, E., WIRTANEN, G., AXELSON-LARSSON, L. and AHVENAINEN, R. Testing of reliability of non-destructive pressure differential package leakage testers with semirigid aseptic cups. Food Control. 1998, 9: 49–55. 16. JENSEN, P. Testing of package integrity based on CO2 as a trace gas. Proc. IAPRI Symp. Reims, 9–12 October 1994, 9 p. 17. SAFVI, A., MEERBAUM, M., MORRIS, S., HARPER, C. and O’BRIEN W. Acoustic imaging of defects in flexible food packages. J. Food Prot. 1997, 60: 309– 14. 18. SONG, Y., LEE, H. and YAM, K. Feasibility of using a non-destructive ultrasonic technique for detecting defective seals. Pack. Techn. Sci. 1993, 6: 37–42. 19. YAM, K.L. Pressure differential techniques for package integrity inspection. In (Blakistone, B.A. and Harper, C.L. eds) Plastic Package Integrity Testing – assuring Seal Quality, Institute of Packaging Professionals, Herndon, VA., pp. 137–46, 1995. 20. HURME, E., WIRTANEN, G. AXELSON-LARSSON, L. and AHVENAINEN, R. Reliability of non-destructive pressure differential package leakage testers using semirigid retort trays. Food Sci. Techn. 1998, 31: 461–6. 21. HURME, E. and AHVENAINEN, R. 1998. A nondestructive leak detection method for flexible food packages using hydrogen as a tracer gas. J. Food Prot. 1998, 61: 1165–9. 284 Novel food packaging techniques
Detecting leaks in modified atmosphere packaging 285 STAUFFER T. Non-destructive in-line detection of leaks in food and beverage packages -an analysis of methods. J. Pack. Techn. 1988, 2: 147- 23. BOJKOW, E, RICHTER, C. and POTZL, G. Helium leak testing of rigid containers. Proc. IAPRI Symp. Vienna, 23-26 September, 16 p. 1984 24. HEIKKINEN E. HURME.E and ahvenainEN R US Patent 6279384 Method for treating a product and a leak-detection device, 2001 ABE,Y. Active packaging with oxygen absorbers. In(Ahvenainen, R Mattila-Sandholm, T. and Ohlsson, T. eds) Minimal Processing of Foods VTT Symposiu um142 Gas Chemical Co, Inc, Tokyo, Japan, 190> ygen Indicator, Mitsubishi 26. GOTO, M. Japanese Patent JP 62-259059. O 27. YOSHIKAWA, Y, NAWATA, T, GOTO, M. and FUJIl, Y, US Patent 4169811 Oxygen Indicator, Mitsubishi Gas Chemical Co, Inc, Tokyo, Japan, 1979 28. DAVIES, E.S. and GARNER, C.D. GB 2298273 Oxygen Indicating Composition. The Victoria University of Manchester, Manchester, UK 1996 29. KRUMHAR, K. C and KAREL, M. US Patent 5096813. Visual Indicator System. Massachusetts Institute of Technology, Cambridge, MA, USA 30. YOSHIKAWA, Y, NAWATA, T, GOTO, M. and Kondo, y US Patent 4349509 Oxygen Indicator Adapted for Printing or Coating and Oxygen-Indicating Device. Mitsubishi Gas Chemical Co, Inc, Tokyo, Japan, 1982 31. NAKAMURA, H, NAKAZAWA, N and KAWAMURA, Y Japanese Patent P 62- 183834. Food Oxidation Indicating Material- Comprises Oxygen Absorption Agent Containing Indicator Composed of Methylene Blue, Reducing Agent and Resin Binder. Toppan Printing Co, Ltd, Tokyo, 1987 32. SHIROZAKI, Y. Japanese Patent JP 2-57975. Oxygen Indicator. Nippon Kayaku KK, Tokyo, Japan, 1990 33. LENARVOR N, HAMON, J.-R. and LaPiNe, C. French Patent FR 2710757 Detecting the presence and disappearance of a gaseous target substance using an indicator which forms a coloured reaction product with the substance, and an antagonist which modifies the colour of the reaction product. ATCO, Caen, France, 1993 MATTILA-SANDHOLM. T. ahvENainEN. R. HURME. E. and jarvi. KAARIAINEN, T. EP 0666977. Oxygen sensitive colour indicator fc detecting leaks in gas-protected food packages. Technical Research Centre of Finland (VTT), Espoo, Finland, 1998 35. PERLMAN, D and LINSCHITZ, H. US Patent 4526752 Oxygen Indicator for 36. AHVENAINEN, R, PULLINEN, T, HURME. E, SMOLANDER, M. and SIIKA-AHO M. WO 9821120. Package for decayable foodstuffs. Technical Research Centre of Finland (VTT), Espoo, Finland, 1998 37. GARDIOL, A.E., HERNANDEZ, R.J., REINHAMMAR, B. and HARTE,BR
22. STAUFFER, T. Non-destructive in-line detection of leaks in food and beverage packages – an analysis of methods. J. Pack. Techn. 1988, 2: 147– 9. 23. BOJKOW, E., RICHTER, C. and PO¨ TZL, G. Helium leak testing of rigid containers. Proc. IAPRI Symp. Vienna, 23–26 September, 16 p. 1984. 24. HEIKKINEN, E., HURME, E. and AHVENAINEN, R. US Patent 6279384. Method for treating a product and a leak-detection device, 2001. 25. ABE, Y. Active packaging with oxygen absorbers. In (Ahvenainen, R., Mattila-Sandholm, T. and Ohlsson, T. eds) Minimal Processing of Foods, VTT Symposium 142. , pp. 209–23, 1994. 26. GOTO, M. Japanese Patent JP 62-259059. Oxygen Indicator, Mitsubishi Gas Chemical Co., Inc., Tokyo, Japan, 1987. 27. YOSHIKAWA, Y., NAWATA, T., GOTO, M. and FUJII, Y. US Patent 4169811. Oxygen Indicator, Mitsubishi Gas Chemical Co., Inc., Tokyo, Japan, 1979. 28. DAVIES, E.S. and GARNER, C.D. GB 2298273 Oxygen Indicating Composition. The Victoria University of Manchester, Manchester, UK, 1996. 29. KRUMHAR, K. C. and KAREL, M. US Patent 5096813. Visual Indicator System. Massachusetts Institute of Technology, Cambridge, MA, USA, 1992. 30. YOSHIKAWA, Y., NAWATA, T., GOTO, M. and KONDO, Y. US Patent 4349509. Oxygen Indicator Adapted for Printing or Coating and Oxygen-Indicating Device. Mitsubishi Gas Chemical Co., Inc., Tokyo, Japan, 1982. 31. NAKAMURA, H., NAKAZAWA, N. and KAWAMURA, Y. Japanese Patent JP 62- 183834. Food Oxidation Indicating Material – Comprises Oxygen Absorption Agent Containing Indicator Composed of Methylene Blue, Reducing Agent and Resin Binder. Toppan Printing Co., Ltd., Tokyo, Japan, 1987. 32. SHIROZAKI, Y. Japanese Patent JP 2-57975. Oxygen Indicator. Nippon Kayaku KK, Tokyo, Japan, 1990. 33. LENARVOR, N., HAMON, J.-R. and LAPINTE, C. French Patent FR 2710751. Detecting the presence and disappearance of a gaseous target substance – using an indicator which forms a coloured reaction product with the substance, and an antagonist which modifies the colour of the reaction product. ATCO, Caen, France, 1993. 34. MATTILA-SANDHOLM, T., AHVENAINEN, R., HURME, E. and JA¨ RVIKA¨ A¨ RIA¨ INEN, T. EP 0666977. Oxygen sensitive colour indicator for detecting leaks in gas-protected food packages. Technical Research Centre of Finland (VTT), Espoo, Finland, 1998. 35. PERLMAN, D. and LINSCHITZ, H. US Patent 4526752. Oxygen Indicator for Packaging, 1985. 36. AHVENAINEN, R., PULLINEN, T., HURME, E., SMOLANDER, M. and SIIKA-AHO, M. WO 9821120. Package for decayable foodstuffs. Technical Research Centre of Finland (VTT), Espoo, Finland, 1998. 37. GARDIOL, A.E., HERNANDEZ, R.J., REINHAMMAR, B. and HARTE, B.R. Detecting leaks in modified atmosphere packaging 285
