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《食品包装技术》（英文版）Chapter 3 Oxygen, ethylene and other scavengers

The best known and most widely used active packaging technologies for foods today are those engineered to remove undesirable substances from the headspace of a package through absorption, adsorption or scavenging. To achieve this goal a physical or chemical absorbent or adsorbent is incorporated in the packaging material or added to the package by means of a sachet. In most publications,

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Oxygen, ethylene and other scavengers 27 S=surface area of the pack in m P= permeability of the packaging in ml/m*/24h/atm D= the shelf-life of the product in days The volume of oxygen to be absorbed is obtained by adding A and B. based on these calculations, the size of the scavenger and the number of sachets can be 3.3.1 Oxygen scavenging sachets In general, O2 scavenging technologies are based on one of the following concepts: iron powder oxidation, ascorbic acid oxidation, catechol oxidation, photosensitive dye oxidation, enzymatic oxidation(e.g. glucose oxidase and alcohol oxidase), unsaturated fatty acids(e.g. oleic acid or linolenic acid)or immobilised yeast on a solid material(Floros et al, 1997). A summary of the most important trademarks of oxygen scavenger systems and their manufacturers is shown in Table 3. 2 The majority of presently available oxygen scavengers are based on the rinciple of iron oxidation(Nakamura and Hoshino, 1983, Rooney, 1995 l.1999 Fe→Fe2 Fe2++2OH→Fe(OH2 Fe(Oh+=02+5H2O- Fe(Oh)3 The principle behind oxygen absorption is iron rust formation. To prevent the on powder from imparting colour to the food, the iron is contained in a sachet The sachet material is highly permeable to oxygen and water vapour. A rule of thumb is that 1 g of iron will react with 300 ml of O2(Labuza, 1987; Nielsen, 1997, Vermeiren et al, 1999). The LDso (lethal dose that kills 50% of the population) for iron is 16 g/kg body weight. The largest commercially available sachet contains 7 grams of iron so this would amount to only 0. 1 g/kg for a person of 70 kg, or 160 times less than the lethal dose(Labuza and breene, 1989). Iron-based oxygen scavengers have one disadvantage: they cannot pass the metal detectors usually installed on the packaging line. This problem can be avoided, e.g. by ascorbic acid or enzyme based O2 scavengers(Hurme and Ahvenainen, 1998) Some important iron-based O2 absorbent sachets are Ageless(Mitsubishi Gas Chemical Co., Japan), ATCO O2 scavenger (Standa Industrie, France), Freshilizer Series (Toppan Printing Co., Japan), Vitalon(Toagosei Chem

S surface area of the pack in m2 ; P permeability of the packaging in ml/m2 =24h/atm; D the shelf-life of the product in days. The volume of oxygen to be absorbed is obtained by adding A and B. Based on these calculations, the size of the scavenger and the number of sachets can be determined. 3.3.1 Oxygen scavenging sachets In general, O2 scavenging technologies are based on one of the following concepts: iron powder oxidation, ascorbic acid oxidation, catechol oxidation, photosensitive dye oxidation, enzymatic oxidation (e.g. glucose oxidase and alcohol oxidase), unsaturated fatty acids (e.g. oleic acid or linolenic acid) or immobilised yeast on a solid material (Floros et al., 1997). A summary of the most important trademarks of oxygen scavenger systems and their manufacturers is shown in Table 3.2. The majority of presently available oxygen scavengers are based on the principle of iron oxidation (Nakamura and Hoshino, 1983; Rooney, 1995; Vermeiren et al., 1999) Fe ! Fe2 2eÿ 1 2 O2 H2O 2eÿ ! 2OHÿ Fe2 2OHÿ ! Fe (OH)2 Fe (OH)2 1 4 O2 1 2 H2O ! Fe (OH)3 The principle behind oxygen absorption is iron rust formation. To prevent the iron powder from imparting colour to the food, the iron is contained in a sachet. The sachet material is highly permeable to oxygen and water vapour. A rule of thumb is that 1 g of iron will react with 300 ml of O2 (Labuza, 1987; Nielsen, 1997; Vermeiren et al., 1999). The LD50 (lethal dose that kills 50% of the population) for iron is 16 g/kg body weight. The largest commercially available sachet contains 7 grams of iron so this would amount to only 0.1 g/kg for a person of 70 kg, or 160 times less than the lethal dose (Labuza and Breene, 1989). Iron-based oxygen scavengers have one disadvantage: they cannot pass the metal detectors usually installed on the packaging line. This problem can be avoided, e.g. by ascorbic acid or enzyme based O2 scavengers (Hurme and Ahvenainen, 1998). Some important iron-based O2 absorbent sachets are AgelessÕ (Mitsubishi Gas Chemical Co., Japan), ATCOÕ O2 scavenger (Standa Industrie, France), FreshilizerÕ Series (Toppan Printing Co., Japan), Vitalon (Toagosei Chem. Oxygen, ethylene and other scavengers 27

Oxygen, ethylene and other scavengers 29 Table 3.3 Types and properties of Ageless oxygen scavenging sachets( rooney, 1995; Ageless technical information, 2002) Type Function Moisture status Water activity speed(day) ZP/ZPT Decreases [O2 <0.9 1-3 Decreases [O2 0.65-0.95 0.5-1.0 Decreases [O2 Self-reacting 0.65-0.95 3(0-4° 0(-25°C FX Decreases [O21 0.5-1.0 FM Decreases [O2 dependent >0. 1.0 E Decreases Decreases [o2 Self-reacting 0.3-0.5 L Decreases [O2] Self-reacting 0.3-0.95 4 number of days to reduce the oxygen level to less than 0.01%(measured at room temperature Japan), /es pan), Sanso-cut(Finetec Co, Japan ), Seaqul(Nippon Soda Co Industry Co. ax(Multisorb technologies Inc, USA)and O-Buster (Dessicate L SA). Some of them will be discussed in detail Ageless can reduce the oxygen in an airtight container down to 0.01%(100 ppm)or less to prolong shelf-life of food products. Several types of Agelessare commercially available and applicable to many types of foods (Labuza and Breene, 1989, Smith et al., 1990: Abe, 1994, Ageless technical information 1994: Rooney, 1995; Smith, 1996). The different types and properties of Ageless oxygen scavenging sachets are shown in Table 3.3 A self-reacting type contains moisture in the sachet and as soon as the sachet is exposed to air, the reaction starts. In moisture-dependent types, oxygen scavenging takes place only after moisture has been taken up from the food These sachets are stable in open air before use because they do not react immediately upon exposure to air therefore they are easy to handle if kept dry Toppan Printing Co developed another type of oxygen scavenging sachet, named Freshilizer. Two series are commercially available, the F series and C series. Sachets of the F series contain ferrous metal and scavenge oxygen without generating another gas. The C series contain non-ferrous particles and are able to sorb oxygen and generate an equal volume of carbon dioxide to prevent package collapse FreshPax is a patented oxygen scavenger developed by Multisorb technologies. Four main types of Fresh Pax are commonly available: type B D,R and M. Type B is used for moist or semi-moist foods with a water activity above 0.7. Type D is recommended for use with dehydrated and dried foods. To scavenge oxygen at refrigerated or frozen storage temperatures, type R should

Industry Co., Japan), Sanso-cut (Finetec Co., Japan), Seaqul (Nippon Soda Co., Japan), FreshPaxÕ (Multisorb technologies Inc., USA) and O-Buster Õ (Dessicare Ltd., USA). Some of them will be discussed in detail. Ageless Õ can reduce the oxygen in an airtight container down to 0.01% (100 ppm) or less to prolong shelf-life of food products. Several types of AgelessÕ are commercially available and applicable to many types of foods (Labuza and Breene, 1989; Smith et al., 1990; Abe, 1994; AgelessÕ technical information, 1994; Rooney, 1995; Smith, 1996). The different types and properties of Ageless Õ oxygen scavenging sachets are shown in Table 3.3. A self-reacting type contains moisture in the sachet and as soon as the sachet is exposed to air, the reaction starts. In moisture-dependent types, oxygen scavenging takes place only after moisture has been taken up from the food. These sachets are stable in open air before use because they do not react immediately upon exposure to air therefore they are easy to handle if kept dry. Toppan Printing Co. developed another type of oxygen scavenging sachet, named FreshilizerÕ. Two series are commercially available, the F series and C series. Sachets of the F series contain ferrous metal and scavenge oxygen without generating another gas. The C series contain non-ferrous particles and are able to sorb oxygen and generate an equal volume of carbon dioxide to prevent package collapse. FreshPaxTM is a patented oxygen scavenger developed by Multisorb technologies. Four main types of FreshPax are commonly available: type B, D, R and M. Type B is used for moist or semi-moist foods with a water activity above 0.7. Type D is recommended for use with dehydrated and dried foods. To scavenge oxygen at refrigerated or frozen storage temperatures, type R should Table 3.3 Types and properties of Ageless oxygen scavenging sachets (Rooney, 1995; Ageless technical information, 2002) Type Function Moisture status Water activity Absorption speeda (day) ZP/ZPT Decreases [O2] Self-reacting < 0.95 1–3 SA Decreases [O2] Self-reacting 0.65–0.95 0.5–1.0 SS Decreases [O2] Self-reacting 0.65–0.95 2–3 (0–4ºC) 10 (ÿ25ºC) FX Decreases [O2] Moisture > 0.85 0.5–1.0 dependent FM Decreases [O2] Moisture dependent > 0.80 1.0 also microwaveable products E Decreases [O2] Self-reacting < 0.3 3–8 Decreases [CO2] G Decreases [O2] Self-reacting 0.3–0.5 1–4 increases [CO2] GL Decreases [O2] Self-reacting 0.3–0.95 2–4 a number of days to reduce the oxygen level to less than 0.01% (measured at room temperature) Oxygen, ethylene and other scavengers 29

30 Novel food packaging be used. Type M can be used for moist or semi-moist foods, which are packaged under modified atmospheres containing carbon dioxide Another scavenging technology is based on catechol oxidation. As catechol is n organic compound, it passes metal detectors. Tamotsu is the only commercial product in Japan based on this technology(Abe, 1994). Tamotsu type D is used for dry products such as spices, freeze-dried foods, tea. These sachets do not require moisture for their oxygen scavenging reaction Another way of controlling the oxygen level in a food package is by zyme technology. A combination of two enzymes, glucose oxidase catalase, has been applied for oxygen removal. In the presence of water, glt oxidase oxidises glucose, that can be originally present or added to the product to gluconic acid and hydrogen peroxide( greenfield and Laurence, 1975; Labuza and Breene, 1989, Nielsen, 1997). The reaction is: 2 glucose +2 02+2 H20-2 gluconic acid 2 H2O2 where glucose is the substrate Since H2O2 is an objectionable end product, catalase is introduced to break down the peroxide(rooney, 1995, Vermeiren et al., 1999) 2 H,O,+catalase -2H20+O,+ catalase Enzymatic systems are usually very sensitive to changes in pH, water activity, temperature and availability of solvents. Most systems require water for their action, and therefore, they cannot be effectively used with low-water content foods(Floros et al., 1997). The enzyme can either be part of the packaging structure or put in an independent sachet. Both polypropylene(PP) and polyethylene(PE)are good substrates for immobilising enzymes ( Labuza and Breene, 1989). A commercially available enzyme-based oxygen absorbent sachet is Bioka(Bioka Ltd, Finland). It is claimed that all components of the reactive powder and the generated reaction products are food-grade substances safe for both the user and the environment (Bioka technical information, 1999) The oxygen scavenger eliminates the oxygen in the headspace of a package and in the actual product in 12-48 hours at 20C and in 24-96 hours at 2-6C. With certain restrictions, the scavenger can also be used in various frozen products When introducing the sachet into a package, temperature may not exceed 60oC because of the heat sensitivity of the enzymes (Bioka technical information, 1999). An advantage is that it contains no iron powder, so it presents no problems for microwave applications and for metal detectors in the production Besides glucose oxidase, other enzymes are able to scavenge oxygen. One such enzyme is alcohol oxidase, which oxidises ethanol to acetaldehyde. It could be used for food products in a wide aw range since it does not require water to operate. If a lot of oxygen has to be absorbed from the package, a great amount of ethanol would be required, which could cause an off-odour in the package. In addition, considerable aldehyde would be produced which could give the food a yoghurt-like odour(Labuza and Breene, 1989)

be used. Type M can be used for moist or semi-moist foods, which are packaged under modified atmospheres containing carbon dioxide. Another scavenging technology is based on catechol oxidation. As catechol is an organic compound, it passes metal detectors. Tamotsu is the only commercial product in Japan based on this technology (Abe, 1994). Tamotsu type D is used for dry products such as spices, freeze-dried foods, tea. These sachets do not require moisture for their oxygen scavenging reaction. Another way of controlling the oxygen level in a food package is by using enzyme technology. A combination of two enzymes, glucose oxidase and catalase, has been applied for oxygen removal. In the presence of water, glucose oxidase oxidises glucose, that can be originally present or added to the product, to gluconic acid and hydrogen peroxide (Greenfield and Laurence, 1975; Labuza and Breene, 1989; Nielsen, 1997). The reaction is: 2 glucose + 2 O2 + 2 H2O ! 2 gluconic acid + 2 H2O2 where glucose is the substrate. Since H2O2 is an objectionable end product, catalase is introduced to break down the peroxide (Rooney, 1995; Vermeiren et al., 1999): 2 H2O2 catalase ! 2 H2O O2 catalase Enzymatic systems are usually very sensitive to changes in pH, water activity, temperature and availability of solvents. Most systems require water for their action, and therefore, they cannot be effectively used with low-water content foods (Floros et al., 1997). The enzyme can either be part of the packaging structure or put in an independent sachet. Both polypropylene (PP) and polyethylene (PE) are good substrates for immobilising enzymes (Labuza and Breene, 1989). A commercially available enzyme-based oxygen absorbent sachet is Bioka (Bioka Ltd., Finland). It is claimed that all components of the reactive powder and the generated reaction products are food-grade substances safe for both the user and the environment (Bioka technical information, 1999). The oxygen scavenger eliminates the oxygen in the headspace of a package and in the actual product in 12–48 hours at 20ºC and in 24–96 hours at 2–6ºC. With certain restrictions, the scavenger can also be used in various frozen products. When introducing the sachet into a package, temperature may not exceed 60ºC because of the heat sensitivity of the enzymes (Bioka technical information, 1999). An advantage is that it contains no iron powder, so it presents no problems for microwave applications and for metal detectors in the production line. Besides glucose oxidase, other enzymes are able to scavenge oxygen. One such enzyme is alcohol oxidase, which oxidises ethanol to acetaldehyde. It could be used for food products in a wide aw range since it does not require water to operate. If a lot of oxygen has to be absorbed from the package, a great amount of ethanol would be required, which could cause an off-odour in the package. In addition, considerable aldehyde would be produced which could give the food a yoghurt-like odour (Labuza and Breene, 1989). 30 Novel food packaging techniques

Oxygen, ethylene and other scavengers 31 te The Pillsbury Company holds a 1994 patent that utilises ascorbic acid as lucing agent(Graf, 1994). The product, also referred to as Oxysorb, comprises a combination of a reducing agent, ascorbic acid, and a small amount of a transition metal, such as copper. The oxygen removing system may be added The oxidation of polyunsaturated fatty acids(PUFAs)is another technique to scavenge oxygen. It is an excellent oxygen scavenger for dry foods. Most known oxygen scavengers have a serious disadvantage: when water is absent, their oxygen scavenging reaction does not progress. In the presence of an oxygen scavenging system, the quality of the dry food products may decline rapidly because of the migration of water from the oxygen scavenger into the food Mitsubishi Gas Chemical Co holds a patent that uses PUFAs as a reactive agent The PUFAs, preferably oleic, linoleic or linolenic, are contained in carrier oil such as soybean, sesame or cottonseed oil. The oil and/or PUFA are compounded with a transition metal catalyst and a carrier substance(for example calcium carbonate) to solidify the oxygen scavenger composition. In this way the scavenger can be made into a granule or powder and can be ckaged in sachets(Floros et al., 1997) 3.3.2 Oxygen save nging films It should be noted that the introduction of oxygen scavenger sachets into the food package suffers from the disadvantage of possible accidental ingestion of the contents by the consumer. Another concern is that the sachet could leak out and contaminate the product. When sachets are used, there also needs to be a free flow of air surrounding the sachet in order to scavenge headspace oxygen (Rooney, 1995). To eliminate this problem, oxygen removing agents can be ncorporated into the packaging material such as polymer films, labels, crown corks, liners in closures. These oxygen scavenging materials have the additional advantage that they can be used for all products, including liquid products. The oxygen consuming substrate can be either the polymer itself or some easily oxidisable compound dispersed or dissolved in the packaging material(Nielsen 1997, Hurme and Ahvenainen, 1998) a problem related to the use of O2 scavenging films is that the films should not react with atmospheric oxygen prior to use. This problem has been solved by inclusion of an activation system triggering the O2 consuming capabilities of the film in the packaging system. Activation by illumination or catalysts or reagents, supplied at the time of filling, may be required to start the reaction Illumination of a package that contains a photosensitising dye and a singlet oxygen acceptor results in rapid scavenging of oxygen from the headspace Australian researchers have reported that reaction of iron with ground state O2 is too slow for shelf-life extension(Hurme and Ahvenainen, 1998). The singlet excited state of oxygen, which is obtained by dye sensitisation of ground state oxygen using near infra-red, visible or ultraviolet radiation, is highly reactive and so its chemical reaction with scavengers is rapid (Rooney, 1981). The

The Pillsbury Company holds a 1994 patent that utilises ascorbic acid as reducing agent (Graf, 1994). The product, also referred to as Oxysorb, comprises a combination of a reducing agent, ascorbic acid, and a small amount of a transition metal, such as copper. The oxygen removing system may be added in a small oxygen permeable pouch. The oxidation of polyunsaturated fatty acids (PUFAs) is another technique to scavenge oxygen. It is an excellent oxygen scavenger for dry foods. Most known oxygen scavengers have a serious disadvantage: when water is absent, their oxygen scavenging reaction does not progress. In the presence of an oxygen scavenging system, the quality of the dry food products may decline rapidly because of the migration of water from the oxygen scavenger into the food. Mitsubishi Gas Chemical Co. holds a patent that uses PUFAs as a reactive agent. The PUFAs, preferably oleic, linoleic or linolenic, are contained in carrier oil such as soybean, sesame or cottonseed oil. The oil and/or PUFA are compounded with a transition metal catalyst and a carrier substance (for example calcium carbonate) to solidify the oxygen scavenger composition. In this way the scavenger can be made into a granule or powder and can be packaged in sachets (Floros et al., 1997). 3.3.2 Oxygen scavenging films It should be noted that the introduction of oxygen scavenger sachets into the food package suffers from the disadvantage of possible accidental ingestion of the contents by the consumer. Another concern is that the sachet could leak out and contaminate the product. When sachets are used, there also needs to be a free flow of air surrounding the sachet in order to scavenge headspace oxygen (Rooney, 1995). To eliminate this problem, oxygen removing agents can be incorporated into the packaging material such as polymer films, labels, crown corks, liners in closures. These oxygen scavenging materials have the additional advantage that they can be used for all products, including liquid products. The oxygen consuming substrate can be either the polymer itself or some easily oxidisable compound dispersed or dissolved in the packaging material (Nielsen, 1997; Hurme and Ahvenainen, 1998). A problem related to the use of O2 scavenging films is that the films should not react with atmospheric oxygen prior to use. This problem has been solved by inclusion of an activation system triggering the O2 consuming capabilities of the film in the packaging system. Activation by illumination or catalysts or reagents, supplied at the time of filling, may be required to start the reaction. Illumination of a package that contains a photosensitising dye and a singlet oxygen acceptor results in rapid scavenging of oxygen from the headspace. Australian researchers have reported that reaction of iron with ground state O2 is too slow for shelf-life extension (Hurme and Ahvenainen, 1998). The singletexcited state of oxygen, which is obtained by dye sensitisation of ground state oxygen using near infra-red, visible or ultraviolet radiation, is highly reactive and so its chemical reaction with scavengers is rapid (Rooney, 1981). The Oxygen, ethylene and other scavengers 31

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