Oxygen, ethylene and other scavengers L. Vermeiren, L. heirlings, F. Devlieghere and J. Debevere, Ghent University, Belgium 3.1 Introduction 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, the term absorption is used loosely to describe any system that removes a substance from the headspace. However, there is a clear difference between absorption and adsorption. Adsorption is a two-dimensional phenomenon while absorption is three-dimensional. According to Mortimer(1993),absorption Involv es a substance being take the bulk of involves a substance being taken onto a surface. Both, absorption and adsorption are physical phenomena while scavenging implies a chemical reaction(Brody al, 2001). This chapter focuses mainly on oxygen and ethylene scavenging and finally also discusses carbon dioxide absorbers and odour removers 3.2 Oxygen scavenging technology 3.2.1 Introduction In many cases, food deterioration is caused by the presence of oxygen, as oxygen is responsible for oxidation of food constituents and proliferation of moulds, aerobic bacteria and insects. Modified atmosphere packaging(MAP) and vacuum packaging have been widely adopted to exclude oxygen from the headspace. However, these physical methods of oxygen elimination do not
3.1 Introduction 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, the term ‘absorption’ is used loosely to describe any system that removes a substance from the headspace. However, there is a clear difference between absorption and adsorption. Adsorption is a two-dimensional phenomenon while absorption is three-dimensional. According to Mortimer (1993), absorption involves a substance being taken into the bulk of a phase while adsorption involves a substance being taken onto a surface. Both, absorption and adsorption are physical phenomena while scavenging implies a chemical reaction (Brody et al., 2001). This chapter focuses mainly on oxygen and ethylene scavenging and finally also discusses carbon dioxide absorbers and odour removers. 3.2 Oxygen scavenging technology 3.2.1 Introduction In many cases, food deterioration is caused by the presence of oxygen, as oxygen is responsible for oxidation of food constituents and proliferation of moulds, aerobic bacteria and insects. Modified atmosphere packaging (MAP) and vacuum packaging have been widely adopted to exclude oxygen from the headspace. However, these physical methods of oxygen elimination do not 3 Oxygen, ethylene and other scavengers L. Vermeiren, L. Heirlings, F. Devlieghere and J. Debevere, Ghent University, Belgium
Oxygen, ethylene and other scavengers 23 al ways remove the oxygen completely. Some oxygen (0. 1-2%) generally remains in the package and even more when the food is porous. Moreover, the oxygen that permeates through the packaging film during storage cannot be removed by these techniques. In the presence of such amounts of oxygen, many of the oxidation reactions and mould proliferation still proceed. Oxygen scavengers are able to reduce the oxygen concentration to less than 0.01% and can maintain those levels(Rooney, 1995; Hurme and Ahvenainen, 1998, Vermeiren et al, 1999). An oxygen scavenger is a substance that scavenges oxygen chemically or enzymatically and therefore, protects the packaged food completely against deterioration and quality changes due to oxygen 3.2.2 Role of oxygen scavengers Preventing oxidation Oxygen scavengers effectively prevent oxidative damage in a wide range of food constituents such as(i)oils and fats to prevent rancidity, (ii) both plant and muscle pigments and flavours to prevent discolouration(e.g. meat) and loss of aste and (iii)nutritive elements, e.g., vitamins to prevent loss of the nutritional alue. Berenzon and Saguy(1998)investigated the effect of oxygen scavengers on the shelf-life extension of crackers packaged in hermetically sealed tin cans which were stored at 15, 25 and 35C for up to 52 weeks. Oxygen scavengers reduced the hexanol concentration significantly. Peroxide values were markedly reduced by the presence of oxygen scavengers. In the presence of oxygen scavengers, the lag period before the peroxides started to build up was prolonged to, respectively, 17 and 10 weeks at 25 and 35C. Sensory evaluations showed that in the presence of oxygen scavengers and independently of storage temperature, no oxidative rancid odours were observed for up to 44 weeks Preventing insect damage Oxygen scavengers are effective for killing insects and worms or their eggs growing in cereals such as rice, wheat and soybeans. Fumigation treatments using gases such as bromides and methyl disulfide kill insects but their residues can remain in the food. Additionally, insects in the egg or pupal stages can be resistant against fumigation treatments. Oxygen scavengers are very effective against insects because they remove the oxygen the insects need to survive Prevention of proliferation of moulds and strictly aerobic bacteria Ox ging is effective in preventing growth of moulds and aerobic bacteria. Mould spoilage is an important microbial problem limiting the shelf- life of high and intermediate moisture products. Losses due to mould spoilage are a serious economic concern in the bakery industry. Some moulds, such as Aspergillus flavus and Aspergillus parasiticus, can also produce highly toxic substances called mycotoxins. In gas packaging aerobic growth can still occur depending on the residual oxygen level in the package headspace. It has been demonstrated that moulds can proliferate in headspaces with oxygen
always remove the oxygen completely. Some oxygen (0.1–2%) generally remains in the package and even more when the food is porous. Moreover, the oxygen that permeates through the packaging film during storage cannot be removed by these techniques. In the presence of such amounts of oxygen, many of the oxidation reactions and mould proliferation still proceed. Oxygen scavengers are able to reduce the oxygen concentration to less than 0.01% and can maintain those levels (Rooney, 1995; Hurme and Ahvenainen, 1998; Vermeiren et al., 1999). An oxygen scavenger is a substance that scavenges oxygen chemically or enzymatically and therefore, protects the packaged food completely against deterioration and quality changes due to oxygen. 3.2.2 Role of oxygen scavengers Preventing oxidation Oxygen scavengers effectively prevent oxidative damage in a wide range of food constituents such as (i) oils and fats to prevent rancidity, (ii) both plant and muscle pigments and flavours to prevent discolouration (e.g. meat) and loss of taste and (iii) nutritive elements, e.g., vitamins to prevent loss of the nutritional value. Berenzon and Saguy (1998) investigated the effect of oxygen scavengers on the shelf-life extension of crackers packaged in hermetically sealed tin cans which were stored at 15, 25 and 35ºC for up to 52 weeks. Oxygen scavengers reduced the hexanol concentration significantly. Peroxide values were markedly reduced by the presence of oxygen scavengers. In the presence of oxygen scavengers, the lag period before the peroxides started to build up was prolonged to, respectively, 17 and 10 weeks at 25 and 35ºC. Sensory evaluations showed that in the presence of oxygen scavengers and independently of storage temperature, no oxidative rancid odours were observed for up to 44 weeks. Preventing insect damage Oxygen scavengers are effective for killing insects and worms or their eggs growing in cereals such as rice, wheat and soybeans. Fumigation treatments using gases such as bromides and methyl disulfide kill insects but their residues can remain in the food. Additionally, insects in the egg or pupal stages can be resistant against fumigation treatments. Oxygen scavengers are very effective against insects because they remove the oxygen the insects need to survive. Prevention of proliferation of moulds and strictly aerobic bacteria Oxygen scavenging is effective in preventing growth of moulds and aerobic bacteria. Mould spoilage is an important microbial problem limiting the shelflife of high and intermediate moisture products. Losses due to mould spoilage are a serious economic concern in the bakery industry. Some moulds, such as Aspergillus flavus and Aspergillus parasiticus, can also produce highly toxic substances called mycotoxins. In gas packaging aerobic growth can still occur depending on the residual oxygen level in the package headspace. It has been demonstrated that moulds can proliferate in headspaces with oxygen Oxygen, ethylene and other scavengers 23
24 Novel food packaging techniques concentrations as low as 1-2%(Smith, 1996). Oxygen levels of 0. 1% or lower are required to prevent the growth and mycotoxin production of many moulds (Rooney, 1995). The effects of modified atmosphere packaging involving oxygen scavengers, age temperature and packaging film barrier characteristics on the growth of and aflatoxin production by Aspergillus parasiticus in packaged peanuts was investigated(Ellis et al, 1994). A slight mould growth was visible in air-packaged peanuts using a high gas barrier film (Oxygen Transmission Rate (OTR) of 3-6 cc. m. day at 23C and dry conditions)while extensive growth was observed in peanuts packaged under similar air conditions using a low gas barrier film(OTR of 4000 cc m-day-) When an oxygen scavenger(Ageless type S)was incorporated, mould growth was inhibited in peanuts packaged in a high gas barrier film and was reduced when a low barrier film was used. Aflatoxin B1 production was inhibited in peanuts packaged in a high barrier film with an oxygen scavenger, while a limited amount of aflatoxin less than the regulatory level of 20 ng g was detected in absorbent packaged peanuts using a low barrier film. This study showed that oxygen scavengers are effective for controlling the growth of and aflatoxin production by Aspergillus parasiticus. However, the effectiveness of the scavengers will be dependent on the gas barrier properties of the packaging Smith et al.(1986) showed that oxygen scavengers are three times more effective than gas packaging for increasing the mould-free shelf-life of crusty rolls. In gas packaged (40% N2/60% CO2)crusty rolls with Ageless the headspace oxygen never increased beyond 0.05% and the product remained mould-free for over 60 days at ambient storage temperature. A similar mould- free shelf-life was obtained in air and N2 packaged crusty rolls with Ageless The mould-free shelf-life of white bread packaged in a polypropylene film could be extended from 4-5 days at room temperature to 45 days by using an Ageless sachet. Pizza crust, which moulds in 2-3 days at 30oC was mould-free for over 10 days using an appropriate O2 scavenger(Nakamura and Hoshino, 1983) It is well known that an oxygen-free atmosphere at a water activity greater than 0.92 can favour the growth of many microbial pathogens including Clostridium botulinum (Labuza and Breene, 1989). Clostridium botulinum mainly grows under anaerobic conditions but can also have a limited growth under low O2 conditions. The use of oxygen scavengers could be dangerous if the temperature is not kept close to 0oC. Daifas et al.(1999)investigated the growth and toxin production by Clostridium botulinum in English-style crumpets, using an Ageless FX200 oxygen scavenger at room temperature All inoculated crumpets were toxic within 4 to 6 days and were organoleptically acceptable at the time of toxigenesis. Counts of C. botulinum increased to approximately 105 CFUIg at the time of toxin production. This study confirms that C. botulinum could pose a public health hazard in high aw - high pH crumpets using an oxygen scavenger when stored at non-chilled conditions Lyver et al.(1998)have done challenge studies on raw surimi nuggets, which were inoculated with 10" spores/g of Clostridium botulinum type E spores. All
concentrations as low as 1–2% (Smith, 1996). Oxygen levels of 0.1% or lower are required to prevent the growth and mycotoxin production of many moulds (Rooney, 1995). The effects of modified atmosphere packaging involving oxygen scavengers, storage temperature and packaging film barrier characteristics on the growth of and aflatoxin production by Aspergillus parasiticus in packaged peanuts was investigated (Ellis et al., 1994). A slight mould growth was visible in air-packaged peanuts using a high gas barrier film (Oxygen Transmission Rate (OTR) of 3–6 cc. mÿ2 . dayÿ1 at 23ºC and dry conditions) while extensive growth was observed in peanuts packaged under similar air conditions using a low gas barrier film (OTR of 4000 cc mÿ2 dayÿ1 ). When an oxygen scavenger (AgelessÕ type S) was incorporated, mould growth was inhibited in peanuts packaged in a high gas barrier film and was reduced when a low barrier film was used. Aflatoxin B1 production was inhibited in peanuts packaged in a high barrier film with an oxygen scavenger, while a limited amount of aflatoxin less than the regulatory level of 20 ng. gÿ1 was detected in absorbent packaged peanuts using a low barrier film. This study showed that oxygen scavengers are effective for controlling the growth of and aflatoxin production by Aspergillus parasiticus. However, the effectiveness of the scavengers will be dependent on the gas barrier properties of the packaging film. Smith et al. (1986) showed that oxygen scavengers are three times more effective than gas packaging for increasing the mould-free shelf-life of crusty rolls. In gas packaged (40% N2/60% CO2) crusty rolls with Ageless Õ the headspace oxygen never increased beyond 0.05% and the product remained mould-free for over 60 days at ambient storage temperature. A similar mouldfree shelf-life was obtained in air and N2 packaged crusty rolls with AgelessÕ. The mould-free shelf-life of white bread packaged in a polypropylene film could be extended from 4–5 days at room temperature to 45 days by using an AgelessÕ sachet. Pizza crust, which moulds in 2–3 days at 30ºC was mould-free for over 10 days using an appropriate O2 scavenger (Nakamura and Hoshino, 1983). It is well known that an oxygen-free atmosphere at a water activity greater than 0.92 can favour the growth of many microbial pathogens including Clostridium botulinum (Labuza and Breene, 1989). Clostridium botulinum mainly grows under anaerobic conditions but can also have a limited growth under low O2 conditions. The use of oxygen scavengers could be dangerous if the temperature is not kept close to 0ºC. Daifas et al. (1999) investigated the growth and toxin production by Clostridium botulinum in English-style crumpets, using an AgelessÕ FX200 oxygen scavenger at room temperature. All inoculated crumpets were toxic within 4 to 6 days and were organoleptically acceptable at the time of toxigenesis. Counts of C. botulinum increased to approximately 105 CFU/g at the time of toxin production. This study confirms that C. botulinum could pose a public health hazard in high aw – high pH crumpets using an oxygen scavenger when stored at non-chilled conditions. Lyver et al. (1998) have done challenge studies on raw surimi nuggets, which were inoculated with 104 spores/g of Clostridium botulinum type E spores. All 24 Novel food packaging techniques
Oxygen, ethylene and other scavengers 25 Table 3.1 Effects of oxygen scavengers on foods(Abe, 1994; Smith et al, 1990) Effect Typical application Fresh taste and aroma arious food items, coffee, tea lusts, cheese, processed Nuts, fried foods, processed meat, whole er produc duration Processed meat, green noodle, herbs, tea, ← Insect damage Beans, grain, herbs, spices Maintaining nutritional value All kinds of foods products were packaged in air and air with an Ageless Ss oxygen absorber and stored at 4, 12 and 25C. Toxin was not detected in any raw product throughout stor 8 days). The absence of toxigenesis was attributed to the low pH (4.1 4.3)due mainly to the growth of lactic acid bacteria. Whiting and naftulil (1992) showed that controlling the pH and NaCl concentration of the food product is an important factor in controlling growth of C. botulinum under low oxygen concentrations. When oxygen absorbers are used, challenge studies should be done to investigate if C. botulinum is able to grow. An overview of the effects of oxygen scavengers and their most important food applications is shown in Table 3.1 3.3 Selecting the right type of oxygen scavenger Oxygen scavengers must satisfy several requirements: they must 1. be harmless to the human body. Though the oxygen scavengers themselves are neither food nor food additives, they are placed together with food in a package, and there is therefore the possibility of accidental intake 2. absorb oxygen at an appropriate rate. If the reaction is too fast, there will be a loss of oxygen absorption capacity during introduction into the package. If it is too slow, the food will not be adequately protected from oxygen 3. not produce toxic substances or unfavourable gas or odour. performance 5. absorb a large amount of oxygen 6. be economically priced(Nakamura and Hoshino, 1983: Abe, 1994; Rooney An appropriate oxygen scavenger is chosen depending on the O2-level in the headspace, how much oxygen is trapped in the food initially and the amount of
products were packaged in air and air with an AgelessÕ SS oxygen absorber and stored at 4, 12 and 25ºC. Toxin was not detected in any raw product throughout storage (28 days). The absence of toxigenesis was attributed to the low pH (4.1– 4.3) due mainly to the growth of lactic acid bacteria. Whiting and Naftulin (1992) showed that controlling the pH and NaCl concentration of the food product is an important factor in controlling growth of C. botulinum under low oxygen concentrations. When oxygen absorbers are used, challenge studies should be done to investigate if C. botulinum is able to grow. An overview of the effects of oxygen scavengers and their most important food applications is shown in Table 3.1. 3.3 Selecting the right type of oxygen scavenger Oxygen scavengers must satisfy several requirements: they must 1. be harmless to the human body. Though the oxygen scavengers themselves are neither food nor food additives, they are placed together with food in a package, and there is therefore the possibility of accidental intake by consumers. 2. absorb oxygen at an appropriate rate. If the reaction is too fast, there will be a loss of oxygen absorption capacity during introduction into the package. If it is too slow, the food will not be adequately protected from oxygen damage. 3. not produce toxic substances or unfavourable gas or odour. 4. be compact in size and are expected to show a constant quality and performance. 5. absorb a large amount of oxygen. 6. be economically priced (Nakamura and Hoshino, 1983; Abe, 1994; Rooney, 1995). An appropriate oxygen scavenger is chosen depending on the O2-level in the headspace, how much oxygen is trapped in the food initially and the amount of Table 3.1 Effects of oxygen scavengers on foods (Abe, 1994; Smith et al., 1990) Effect Typical application Fresh taste and aroma Various food items, coffee, tea $ Mould growth Bakery products, cheese, processed seafood, pasta $ Rancidity Nuts, fried foods, processed meat, whole milk powder product $ Discolouration Processed meat, green noodle, herbs, tea, dried vegetables $ Insect damage Beans, grain, herbs, spices Maintaining nutritional value All kinds of foods Oxygen, ethylene and other scavengers 25
26 Novel food packaging oxygen that will be transported from the surrounding air into the package during storage. The nature of the food (e. g. size, shape, weight), water activity and desired shelf-life are also important factors influencing the choice of oxygen absorbents For an oxygen scavenger(sachet) to be effective, some conditions have to be fulfilled(Nakamura and Hoshino, 1983 Abe, 1994, Smith, 1996). First of all packaging containers or films with a high oxygen barrier must be used, otherwise the scavenger will rapidly become saturated and lose its ability to trap O2. Films with an oxygen permeability not exceeding 20 ml/md atm are recommended for packages in which an oxygen scavenger will be used. Examples of barrier layers used with oxygen scavengers are VOH(ethylene vinyl alcohol) and PVDC (polyvinylidene chloride)(Nakamura and Hoshino, 1983; Rooney, 1995). If films with high O2 permeabilities are used( 100 ml/m2. d atm), the O2 concentration will reach zero within a week but after some days, it will return to ambient air level because the absorbent is saturated. If high-barrier films(e.g. <10 ml/m=d atm)are used, the headspace O2 will be reduced to 100 ppm within 1-2 days and remain at this level for the duration of the storage period provided that package integrity is maintained(Rooney, 1995). Secondly, for flexible packaging heat sealing should be complete so that no air invades the package through the sealed part. A rapid, inexpensive and efficient method of monitoring package integrity and ensuring low residual headspace oxygen throughout the storage period is through the incorporation of a redox indicator, e.g. Ageless Eye. Ageless Eye is a tablet which indicates the presence of oxygen by a colour change. When placed inside the package, the colour changes from blue to pink when the O2 concentration approaches zero. If the indicator reverts to its blue colour, this is an indication of poor packaging integrity (Smith et al, 1990; Nakamura and Hoshino, 1983, Rooney, 1995). Finally, an oxygen scavenger of the appropriate type and size must be selected. The appropriate size of the scavenger can be calculated using the following formulae(Roussel, 1999; ATCO technical information, 2002). The volume of oxygen present at the time of packaging(A)can be calculated using the formula A=(V-P)×[O2/100 V= volume of the finished pack determined by submersion in water and expressed in ml P= weight of the finished pack in g: Jo2= initial O2 concentration in package(=21% if air) In addition, it is ary to calculate the volume of oxygen likely to permeate through the packaging during the shelf-life of the product(B). Thi quantity in ml may be calculated as follows B=SxP×D
oxygen that will be transported from the surrounding air into the package during storage. The nature of the food (e.g. size, shape, weight), water activity and desired shelf-life are also important factors influencing the choice of oxygen absorbents. For an oxygen scavenger (sachet) to be effective, some conditions have to be fulfilled (Nakamura and Hoshino, 1983; Abe, 1994; Smith, 1996). First of all, packaging containers or films with a high oxygen barrier must be used, otherwise the scavenger will rapidly become saturated and lose its ability to trap O2. Films with an oxygen permeability not exceeding 20 ml/m2 .d.atm are recommended for packages in which an oxygen scavenger will be used. Examples of barrier layers used with oxygen scavengers are EVOH (ethylene vinyl alcohol) and PVDC (polyvinylidene chloride) (Nakamura and Hoshino, 1983; Rooney, 1995). If films with high O2 permeabilities are used (> 100 ml/m2 .d.atm), the O2 concentration will reach zero within a week but after some days, it will return to ambient air level because the absorbent is saturated. If high-barrier films (e.g. < 10 ml/m2 .d.atm) are used, the headspace O2 will be reduced to 100 ppm within 1–2 days and remain at this level for the duration of the storage period provided that package integrity is maintained (Rooney, 1995). Secondly, for flexible packaging heat sealing should be complete so that no air invades the package through the sealed part. A rapid, inexpensive and efficient method of monitoring package integrity and ensuring low residual headspace oxygen throughout the storage period is through the incorporation of a redox indicator, e.g. AgelessÕ EyeÕ. AgelessÕ EyeÕ is a tablet which indicates the presence of oxygen by a colour change. When placed inside the package, the colour changes from blue to pink when the O2 concentration approaches zero. If the indicator reverts to its blue colour, this is an indication of poor packaging integrity (Smith et al., 1990; Nakamura and Hoshino, 1983; Rooney, 1995). Finally, an oxygen scavenger of the appropriate type and size must be selected. The appropriate size of the scavenger can be calculated using the following formulae (Roussel, 1999; ATCOÕ technical information, 2002). The volume of oxygen present at the time of packaging (A) can be calculated using the formula: A V ÿ P O2=100 V volume of the finished pack determined by submersion in water and expressed in ml; P weight of the finished pack in g; O2 initial O2 concentration in package ( 21% if air). In addition, it is necessary to calculate the volume of oxygen likely to permeate through the packaging during the shelf-life of the product (B). This quantity in ml may be calculated as follows: B S P D 26 Novel food packaging techniques
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
Table 3.2 Some manufacturers and trade names of oxygen scavengers(Ahvenainen and urme, 1997; Day, 1998; Vermeiren et al., 1999) Com Trade name Principle/Active substances Mitsubishi Gas Chemical Co, Ltd (Japan) Ageless Sachets and labels Iron based Toppan Printing Co, Ltd. (Japan) Freshilizer Sachets Iron based Toagosei Chem Ind Co (Japan) Vitalin Sachets Nippon Soda Co, Ltd. (Japan) Seaqul Finetec Co, Ltd. (Japan) Sanso-cut Iron based Toyo Pulp Co (Japan) Sachets Catechol Toyo Seikan Kaisha Ltd (Japan) Plastic trays Iron based Dessicare Ltd (US) Iron based Multisorb technologies Inc. (US) FreshMan Labels Iron based Freshpax Sachets Iron based Amoco Chemicals(US) Amosorb Plastic film unknown Ciba Specialty chemicals(Switzerland) Shelfplus Plastic film Iron based W.R. Grace and Co (US) PureSeal Bottle crowns Ascorbate/metallic salts Dare Bottle crowns, bottles Ascorbate/sulphite CSIRO/Southcorp Packaging(Australia) Plastic film Photosensitive dye/ organic compound Sealed Air Co. (US) OS1000 Plastic film Light activated scavenger echnologies (UK) Xbar Plastic bottles Cobalt catalyst/ nylon polymer ATCO Sachets Iron based Bottle crowns Iron based ATCO Labels Iron based Bioka Ltd (Finland) Bioko Sache Enzyme based
Table 3.2 Some manufacturers and trade names of oxygen scavengers (Ahvenainen and Hurme, 1997; Day, 1998; Vermeiren et al., 1999) Company Trade name Type Principle/Active substances Mitsubishi Gas Chemical Co., Ltd. (Japan) Ageless Sachets and labels Iron based Toppan Printing Co., Ltd. (Japan) Freshilizer Sachets Iron based Toagosei Chem. Ind. Co. (Japan) Vitalon Sachets Iron based Nippon Soda Co., Ltd. (Japan) Seaqul Sachets Iron based Finetec Co., Ltd. (Japan) Sanso-cut Sachets Iron based Toyo Pulp Co. (Japan) Tamotsu Sachets Catechol Toyo Seikan Kaisha Ltd. (Japan) Oxyguard Plastic trays Iron based Dessicare Ltd. (US) O-Buster Sachets Iron based Multisorb technologies Inc. (US) FreshMax Labels Iron based FreshPax Sachets Iron based Amoco Chemicals (US) Amosorb Plastic film unknown Ciba Specialty chemicals (Switzerland) Shelfplus O2 Plastic film Iron based W.R. Grace and Co. (US) PureSeal Bottle crowns Ascorbate/metallic salts Darex Bottle crowns, bottles Ascorbate/sulphite CSIRO/Southcorp Packaging (Australia) Zero2 Plastic film Photosensitive dye/ organic compound Cryovac Sealed Air Co. (US) OS1000 Plastic film Light activated scavenger CMB Technologies (UK) Oxbar Plastic bottles Cobalt catalyst/ nylon polymer Standa Industrie (France) ATCO Sachets Iron based Oxycap Bottle crowns Iron based ATCO Labels Iron based Bioka Ltd. (Finland) Bioka Sachets Enzyme based
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. 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 0.85 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
