MAP, product safety and nutritional quality 217 been described as the two treatments which contribute to preserve vitamin Cin fruits and vegetables(Watada, 1987). Delaporte(1971)and others observed that loss of AA can be reduced by storing apples in a reduced oxygen atmosphere However, Haffner et al.(1997) have shown that AA levels in various apple cultivars decreased more under ultra low oxygen (ULO) compared to air storage On the other hand. increasing cO, concentration above a certain threshold seems to have an adverse effect on vitamin c content in some fruits and vegetables. It has been reported that the effect of elevated co2 level and storage temperature and duration (Weichmann, 1986). Bangerth(1977)observed accelerated AA losses in apples and red currants stored in elevated CO atmospheres. Vitamin C content was reduced by high CO2 concentrations (10- 30%CO2)in strawberries and blackberries and only a moderate to negligible effect was found for black currants, red currants and raspberries(Agar et al 1997) torage of sweet pepper for six days at 13.C in CO2 enriched atmospheres resulted in a reduction in AA content(Wang, 1977). Wang(1983)noted that 1% O2 retarded aa degradation in Chinese cabbage stored for three months at 0C He observed that treatments with 10 or 20%CO2 for five or ten days produced no effect, and 30 or 40% CO2 increased AA decomposition. Veltman et al. (1999)have observed a 60% loss in AA content of "Conference pears after storage in 2%O2+10%CO2. There were no data available to show whether a parallel reduction in O2 concentration alleviates the negative CO2 effect. Agar et al.(1997) proposed that reducing O2 concentration in the storage atmosphere in the present of high CO2 had little effect on the vitamin C preservation. The only beneficial effect of low O, alleviating the co, effect could be observed when applying CO2 concentrations lower than 10% In fresh-cut products, high CO2 concentration in the storage atmosphere has also been described to cause degradation of vitamin C. Thus, concentrations of 5, 10 or 20% CO2 caused degradation of vitamin C in fresh-cut kiwifruit slices (Agar et al, 1999). Enhanced losses of vitamin C in response to CO2 higher than 10% may be due to the stimulating effects on oxidation of AA and/or inhibition of Dha reduction to AA(Agar et al., 1999). In addition, vitamin C content decreased in MAP-stored Swiss chard (Gil et al., 1998a)as well as in potato strips(Tudela et al, 2002). In contrast, MAP retarded the conversion of Aa to DHA that occurred in air-stored jalapeno pepper rings(Howard et al., 1994 Howard and Hernandez-Brenes 1998). Wright and Kader(1997a)found no significant losses of vitamin C occurred during the post-cutting life of fresh-cut strawberries and persimmons for eight days in CA (2%O2, air 12%CO2,or 2%O2+ 12%CO2at 0C In studies of cut broccoli florets and intact heads of broccoli CA/maP resulted in greater AA retention and shelf-life extension in contrast to air-stored samples(Barth et al, 1993; Paradis et al, 1996). Retention of Aa was found in fresh-cut lettuce packaged with nitrogen(Barry-Ryan and O Beirne, 1999) They suggest that high levels of CO2(30-40%) increased AA losses by conversion into Dha due to availability of oxygen in lettuce(Barry-Ryan andbeen described as the two treatments which contribute to preserve vitamin C in fruits and vegetables (Watada, 1987). Delaporte (1971) and others observed that loss of AA can be reduced by storing apples in a reduced oxygen atmosphere. However, Haffner et al. (1997) have shown that AA levels in various apple cultivars decreased more under ultra low oxygen (ULO) compared to air storage. On the other hand, increasing CO2 concentration above a certain threshold seems to have an adverse effect on vitamin C content in some fruits and vegetables. It has been reported that the effect of elevated CO2 level and storage temperature and duration (Weichmann, 1986). Bangerth (1977) observed accelerated AA losses in apples and red currants stored in elevated CO2 atmospheres. Vitamin C content was reduced by high CO2 concentrations (10– 30% CO2) in strawberries and blackberries and only a moderate to negligible effect was found for black currants, red currants and raspberries (Agar et al., 1997). Storage of sweet pepper for six days at 13ºC in CO2 enriched atmospheres resulted in a reduction in AA content (Wang, 1977). Wang (1983) noted that 1% O2 retarded AA degradation in Chinese cabbage stored for three months at 0ºC. He observed that treatments with 10 or 20% CO2 for five or ten days produced no effect, and 30 or 40% CO2 increased AA decomposition. Veltman et al. (1999) have observed a 60% loss in AA content of ‘Conference’ pears after storage in 2% O2 + 10% CO2. There were no data available to show whether a parallel reduction in O2 concentration alleviates the negative CO2 effect. Agar et al. (1997) proposed that reducing O2 concentration in the storage atmosphere in the present of high CO2 had little effect on the vitamin C preservation. The only beneficial effect of low O2 alleviating the CO2 effect could be observed when applying CO2 concentrations lower than 10%. In fresh-cut products, high CO2 concentration in the storage atmosphere has also been described to cause degradation of vitamin C. Thus, concentrations of 5, 10 or 20% CO2 caused degradation of vitamin C in fresh-cut kiwifruit slices (Agar et al., 1999). Enhanced losses of vitamin C in response to CO2 higher than 10% may be due to the stimulating effects on oxidation of AA and/or inhibition of DHA reduction to AA (Agar et al., 1999). In addition, vitamin C content decreased in MAP-stored Swiss chard (Gil et al., 1998a) as well as in potato strips (Tudela et al., 2002). In contrast, MAP retarded the conversion of AA to DHA that occurred in air-stored jalapeno pepper rings (Howard et al., 1994; Howard and Hernandez-Brenes 1998). Wright and Kader (1997a) found no significant losses of vitamin C occurred during the post-cutting life of fresh-cut strawberries and persimmons for eight days in CA (2% O2, air + 12% CO2, or 2% O2 + 12% CO2) at 0ºC. In studies of cut broccoli florets and intact heads of broccoli CA/MAP resulted in greater AA retention and shelf-life extension in contrast to air-stored samples (Barth et al., 1993; Paradis et al., 1996). Retention of AA was found in fresh-cut lettuce packaged with nitrogen (Barry-Ryan and O’Beirne, 1999). They suggest that high levels of CO2 (30–40%) increased AA losses by conversion into DHA due to availability of oxygen in lettuce (Barry-Ryan and MAP, product safety and nutritional quality 217