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×Doxygen 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 ˆ …V ÿ P† ‰O2Š=100 V ˆ volume of the finished pack determined by submersion in water and expressed in ml; P ˆ weight of the finished pack in g; ‰O2Š ˆ initial O2 concentration in package ( ˆ 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 ˆ S P D 26 Novel food packaging techniques