Active packaging and colour control: the case of fruit and vegetables 425 lowered the difference between ideal mushroom target and sample than those observed for mushrooms stored in conventional packages (non-MAP). The improved colour might also be due to lower microbial growth resulting from low O2(Roy et al, 1996) Strawberries stored under low O, 2kPa showed a better colour, high anthocyanin concentration and organic acids content than those stored in air Fruits became darker red and accumulated anthocyanin, although O2 was not as effective at high COz levels in reducing decay(Holcroft and Kader, 1999b Freshly harvested white asparagus spears stored in air or in CA having increased O2 concentrations(1 to 15kPa)showed a concomitant increment in anthocyanin content, resulting in an intense purple colour of the tips. Hue values were lower than those at harvest. with a decline in l* values The lowest anthocyanin accumulation was observed at the tips of the spears stored under the lowest O, level (Siomos et al., 2000) days of strongly reduced from 90% in air to 35% under 2kPa O2 and OkPa CO2 (Verlinden et al, 2001). Fresh processed potato slices stored in MAP with low O, showed a better colour retention when the o, level was lowered from 3.5 to 1. 4kPa, probably due to reduction of oxidase activity such as PPO, ascorbic acid oxidase(AAO, EC 1.10.3.3)and glycolic acid oxidase(GAO, EC 1. 15) Slices in air showed a decrease in L* compared to MAP. It was advantageous to have almost no initial O2 within packages by flushing N2. This active MAP was very important for the keeping quality of slices, taking into consideration that residual O2 in the packages was enough to prevent anaerobiose( Gunes and Lee 1997) To prevent browning of minimally processed potatoes, dipping in some chemical agents was essential because MAP alone did not avoid this disorder Browning is closely related with O2 and COz levels in the package and Oz must be decreased to an acceptable minimum level as soon as possible, it being advantageous to have almost no O2 initially within packages( Gunes and Lee, The intensity of browning of ready-to-eat apples depends on the atmosphere omposition. Apple cubes in MAP were efficiently preserved from browning and showed the lowest colour losses when initially displacing O2 by injecting 100kPa N2 and a film with low O2 permeability was used. This atmosphere was the main factor affecting lightness, and l' changes occurred four times more slowly than when O2 was about 2kPa or when medium O2 permeability films were used( Soliva-Fortuny et al., 2001) It has been suggested that O2 levels greater than 2lkPa may influence the postharvest life of intact and fresh processed fruit and vegetables and PPO may be substrate-inhibited by high O2 levels(Day, 1994). Superatmospheric could have an effect on respiratory activity and ethylene synthesis and action, although response depends on the commodity, ripening stage, O2 level, length of storage and temperature. Levels of COz and C2 Ha should also be considered When focusing on pigment changes, Kader and Ben-Yehoshua(2000)reportedlowered the difference between ideal mushroom target and sample than those observed for mushrooms stored in conventional packages (non-MAP). The improved colour might also be due to lower microbial growth resulting from low O2 (Roy et al., 1996). Strawberries stored under low O2 2kPa showed a better colour, high anthocyanin concentration and organic acids content than those stored in air. Fruits became darker red and accumulated anthocyanin, although O2 was not as effective at high CO2 levels in reducing decay (Holcroft and Kader, 1999b). Freshly harvested white asparagus spears stored in air or in CA having increased O2 concentrations (1 to 15kPa) showed a concomitant increment in anthocyanin content, resulting in an intense purple colour of the tips. Hue values were lower than those at harvest, with a decline in L* values. The lowest anthocyanin accumulation was observed at the tips of the spears stored under the lowest O2 level (Siomos et al., 2000). Red discolouration of chicory after seven days of storage at 12ºC was strongly reduced from 90% in air to 35% under 2kPa O2 and 0kPa CO2 (Verlinden et al., 2001). Fresh processed potato slices stored in MAP with low O2 showed a better colour retention when the O2 level was lowered from 3.5 to 1.4kPa, probably due to reduction of oxidase activity such as PPO, ascorbic acid oxidase (AAO, EC 1.10.3.3) and glycolic acid oxidase (GAO, EC 1.1.3.15). Slices in air showed a decrease in L* compared to MAP. It was advantageous to have almost no initial O2 within packages by flushing N2. This active MAP was very important for the keeping quality of slices, taking into consideration that residual O2 in the packages was enough to prevent anaerobiose (Gunes and Lee, 1997). To prevent browning of minimally processed potatoes, dipping in some chemical agents was essential because MAP alone did not avoid this disorder. Browning is closely related with O2 and CO2 levels in the package and O2 must be decreased to an acceptable minimum level as soon as possible, it being advantageous to have almost no O2 initially within packages (Gunes and Lee, 1997). The intensity of browning of ready-to-eat apples depends on the atmosphere composition. Apple cubes in MAP were efficiently preserved from browning and showed the lowest colour losses when initially displacing O2 by injecting 100kPa N2 and a film with low O2 permeability was used. This atmosphere was the main factor affecting lightness, and L* changes occurred four times more slowly than when O2 was about 2kPa or when medium O2 permeability films were used (Soliva-Fortuny et al., 2001). It has been suggested that O2 levels greater than 21kPa may influence the postharvest life of intact and fresh processed fruit and vegetables and PPO may be substrate-inhibited by high O2 levels (Day, 1994). Superatmospheric O2 could have an effect on respiratory activity and ethylene synthesis and action, although response depends on the commodity, ripening stage, O2 level, length of storage and temperature. Levels of CO2 and C2H4 should also be considered. When focusing on pigment changes, Kader and Ben-Yehoshua (2000) reported Active packaging and colour control: the case of fruit and vegetables 425