Studies were conducted to determine the effect of various levels of headspace oxygen (0–100%, balance CO2) or film oxygen transmission rate (OTR) on the time to toxicity in modified atmosphere packaged (MAP) fresh trout fillets challenged with C. botulinum type E (102 spore/g) and stored under moderate temperature abuse conditions (12C). In all cases, trout were toxic within 5 days, irrespective of the initial levels of oxygen in the package headspace. However, spoilage preceded toxigenesis. Packaging of trout fillets in low gas barrier films, with OTRs ranging from 4,000 to 10,000 cc/m2/day at 24C and 0% relative humidity, also had no effect on time to toxicity in all MAP trout fillets. All fillets were toxic within 4–5 days and spoilage again preceded toxigenesis. This study has shown that the addition of headspace O2, either directly to a package or indirectly by using a low gas barrier film, had no influence on the time to toxigenesis or spoilage. Additional barriers, other than headspace O2 or film transmission rate, need to be considered to ensure the safety of MAP trout fillets, particularty at moderate temperature abuse conditions.

Studies were done to determine the effect of film oxygen transmission rate (OTR) on the time to toxicity in vacuum packaged cold and hot smoked rainbow trout fillets challenged with C. botulinum type E (102 spores/g) and stored at refrigerated conditions (4C), and under mild (8C) and moderate (12C) temperature abuse conditions. While no samples were toxic at 4C, toxin was detected within 28 days at 8C for cold smoked trout fillets vacuum packaged in films with high OTR. Toxin was also detected for most vacuum packaged hot smoked trout fillets within 14–28 days at 8C, with the exception of trout fillets packaged in films with an OTR > 10,000 cc/m2/day. In most cases at 8C, spoilage, based on odor/color scores, preceded or occurred simultaneously with toxigenesis. At 12C all cold and hot smoked trout were toxic after 14–21 days and samples packaged in films with an OTR <5000 cc/m2/day became toxic before, or at the same time as, samples became spoiled. This study has shown that vacuum packaging of trout fillets in low gas barrier films, ranging in OTR from approximately 3,000 to approximately 10,000 cc/m2/day at 24C and 0% relative humidity (RH), did not prevent the growth and toxin production by C. botulinum in vacuum packaged cold and hot smoked trout fillets at 12C. Additional barriers, other than the OTR of the packaging film, need to be considered to ensure the safety of vacuum packaged trout fillets, particularly at mild to moderate temperature abuse storage conditions.