Modified atmosphere packaging (MAP) 351 pathogens, which may result in the food becoming unsafe for consumption before it appears to be organoleptically unacceptable. Most of the pathogenic bacteria can be inhibited by low temperatures(<7C). At these conditions, only psy- chrotrophic pathogens can proliferate. The effect of CO2 on the different psychrotrophic foodborne pathogens is described belo 16.5.1 Clostridium botulinum Dne major concern is the suitability of MAP in the food industry. This is mainly due to the possibility that psychrotrophic, non-proteolytic strains of C. botulinum types B, E, and F are able to grow and produce toxins under MAP conditions Little is known about the effects of modified atmosphere storage conditions on toxin production by C. botulinum. The possibility of inhibiting C botulinum by incorporating low levels of O2 in the package does 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%0 O2 Toxin production by C. botulinum type E, prior to spoilage, has been described in 3 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, par ticularly 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 modi fied atmosphere(vacuum, 100% CO2, or 70% CO2 30%0 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 fillet 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% CO/70% N2)in cooked turkey at 4C but not at 10 C nor at 15C (Lawlor et al, 2000). Recent results in a study by Gibson et al(2000)also ndicated 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 16.5.2 Listeria monocytogenes Listeria monocytogenes is considered a psychrotrophic foodborne pathogen Growth is possible at 1C( Varnam and Evans, 1991)and has even been reported at temperatures as low as -15C(Hudson et al, 1994). The growth of L. mono- cytogenes 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 bypathogens, which may result in the food becoming unsafe for consumption before it appears to be organoleptically unacceptable. Most of the pathogenic bacteria can be inhibited by low temperatures (<7 °C). At these conditions, only psy￾chrotrophic pathogens can proliferate. The effect of CO2 on the different psychrotrophic foodborne pathogens is described below. 16.5.1 Clostridium botulinum One major concern is the suitability of MAP in the food industry. This is mainly due to the possibility that psychrotrophic, non-proteolytic strains of C. botulinum types B, E, and F are able to grow and produce toxins under MAP conditions. Little is known about the effects of modified atmosphere storage conditions on toxin production by C. botulinum. The possibility of inhibiting C. botulinum by incorporating low levels of O2 in the package does 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 3 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, par￾ticularly 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 modi- fied atmosphere (vacuum, 100% CO2, or 70% CO2/30% air). In Tilapia fillets, a modified atmosphere (75% CO2/25% N2), at 8 °C, 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 4 °C (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 4 °C but not at 10 °C 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. 16.5.2 Listeria monocytogenes Listeria monocytogenes is considered a psychrotrophic foodborne pathogen. Growth is possible at 1 °C (Varnam and Evans, 1991) and has even been reported at temperatures as low as -1.5 °C (Hudson et al, 1994). The growth of L. mono￾cytogenes 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 Modified atmosphere packaging (MAP) 351