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 oxygenalways 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 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 Oxygen, ethylene and other scavengers 23