MAP, product safety and nutritional quality 211 not appear to be feasible. Miller(1988, cited by Connor et al., 1989)reported that psychrotrophic strains of C. botulinum are able to produce toxins in an environment with up to 10%O2. Toxin production by C. botulinum type E,prior to spoilage, has been described in three types of fish, at O2 levels of 2% and 4% OConnor-Shaw and Reyes, 2000). Dufresne et al.(2000) also proposed that additional barriers, other than headspace O2 and film, need to be considered to ensure the safety of MAP trout fillets, particularly at moderate temperature The probability of one spore of non-proteolytic C. botulinum(types B, E and F) being toxicogenic in rock fish was outlined in a report by Ikawa and Genigeorgis(1987). The results showed that the toxigenicity was significantly affected(P<0.005)by temperature and storage time, but not by the used modified atmosphere (vacuum, 100%CO2, or 70% CO2/30% air). In Tilapia fillets, a modified atmosphere(75% CO2/25% N2), at 8C, delayed toxin formation by C. botulinum type E, from 17 to 40 days, when compared to vacuum packaged fillets(Reddy et al, 1996). Similar inhibiting effects were recorded for salmon fillets and catfish fillets, at 4C (Reddy et al., 1997a and 1997b). Toxin production from non-proteolytic C. botulinum type B spores was also retarded by a CO2 enriched atmosphere(30% Co2/70% N2)in cooked turkey at 4C but not at 10C nor at 15.C (Lawlor et al, 2000). Recent results in a study by gibson et al.(2000)also indicated that 100% CO2 slows the growth rate of C. botulinum, and that this inhibitory effect is further enhanced with appropriate NaCl concentrations and chilled temperatures Listeria monocytogenes is considered a psychrotrophic foodborne pathogen Growth is possible at 1oC (Varnam and Evans, 1991) and has even been reported at temperatures as low as-15C (Hudson et al, 1994 ) The growth of L. monocytogenes in food products, packaged under modified atmospheres, has of several, although in some cases contradicting, stu de fernando et al., 1995). In general, L. monocytogenes is not greatly inhibited by CO2 enriched atmospheres(zhao et al, 1992)although when combined with other factors such as low temperature, decreased water activity and the addition of Na lactate the inhibiting effect of CO2 is significant (Devlieghere et al 2001). Listeria growth in anaerobic CO2 enriched atmosphere has been demonstrated in lamb in an atmosphere of 50: 50 CO2/N2, at 5C (Nychas 1994): in frankfurter type sausages in atmospheres of distinct proportions of CO2/N2, at 4, 7 and 10oC(Kramer and Baumgart, 1992)and in pork in an atmosphere of 40: 60 CO2/N2, at 4C(Manu-Tawiah et al., 1993).However other authors have not detected growth in chicken anaerobically packaged in 30:70 CO /N2, at 6C(Hart et al., 1991); in 75: 25 CO et al, 1990)and at 4C in 100% CO, in raw minced meat(franco-abuin et al. 997)or in buffered tryptose broth (Szabo and Cahill, 1998). Several investigations demonstrated possible growth of L. monocytogenes on modified atmosphere packaged fresh-cut vegetables, although the results depended very much on the type of vegetables and the storage temperature( Berrang et al. 1989a, Beuchat and Brackett, 1990; Omary et al., 1993, Carlin et al, 1995not appear to be feasible. Miller (1988, cited by Connor et al., 1989) reported that psychrotrophic strains of C. botulinum are able to produce toxins in an environment with up to 10% O2. Toxin production by C. botulinum type E, prior to spoilage, has been described in three types of fish, at O2 levels of 2% and 4% (O’Connor-Shaw and Reyes, 2000). Dufresne et al. (2000) also proposed that additional barriers, other than headspace O2 and film, need to be considered to ensure the safety of MAP trout fillets, particularly at moderate temperature abuse conditions. The probability of one spore of non-proteolytic C. botulinum (types B, E and F) being toxicogenic in rock fish was outlined in a report by Ikawa and Genigeorgis (1987). The results showed that the toxigenicity was significantly affected (P<0.005) by temperature and storage time, but not by the used modified atmosphere (vacuum, 100% CO2, or 70% CO2/30% air). In Tilapia fillets, a modified atmosphere (75% CO2/25% N2), at 8ºC, delayed toxin formation by C. botulinum type E, from 17 to 40 days, when compared to vacuum packaged fillets (Reddy et al., 1996). Similar inhibiting effects were recorded for salmon fillets and catfish fillets, at 4ºC (Reddy et al., 1997a and 1997b). Toxin production from non-proteolytic C. botulinum type B spores was also retarded by a CO2 enriched atmosphere (30% CO2/70% N2) in cooked turkey at 4ºC but not at 10ºC nor at 15ºC (Lawlor et al., 2000). Recent results in a study by Gibson et al. (2000) also indicated that 100% CO2 slows the growth rate of C. botulinum, and that this inhibitory effect is further enhanced with appropriate NaC1 concentrations and chilled temperatures. Listeria monocytogenes is considered a psychrotrophic foodborne pathogen. Growth is possible at 1ºC (Varnam and Evans, 1991) and has even been reported at temperatures as low as ÿ1.5C (Hudson et al., 1994). The growth of L. monocytogenes in food products, packaged under modified atmospheres, has been the focus of several, although in some cases contradicting, studies (Garcia de Fernando et al., 1995). In general, L. monocytogenes is not greatly inhibited by CO2 enriched atmospheres (Zhao et al., 1992) although when combined with other factors such as low temperature, decreased water activity and the addition of Na lactate the inhibiting effect of CO2 is significant (Devlieghere et al., 2001). Listeria growth in anaerobic CO2 enriched atmosphere has been demonstrated in lamb in an atmosphere of 50:50 CO2/N2, at 5ºC (Nychas, 1994); in frankfurter type sausages in atmospheres of distinct proportions of CO2/N2, at 4, 7 and 10ºC (Kra¨mer and Baumgart, 1992) and in pork in an atmosphere of 40:60 CO2/N2, at 4ºC (Manu-Tawiah et al., 1993). However, other authors have not detected growth in chicken anaerobically packaged in 30:70 CO2/N2, at 6ºC (Hart et al., 1991); in 75:25 CO2/N2 at 4ºC (Wimpfheimer et al., 1990) and at 4ºC in 100% CO2 in raw minced meat (Franco-Abuin et al., 1997) or in buffered tryptose broth (Szabo and Cahill, 1998). Several investigations demonstrated possible growth of L. monocytogenes on modified atmosphere packaged fresh-cut vegetables, although the results depended very much on the type of vegetables and the storage temperature (Berrang et al., 1989a; Beuchat and Brackett, 1990; Omary et al., 1993; Carlin et al., 1995; MAP, product safety and nutritional quality 211