Thermal Inactivation of Nonproteolytic Clostridium botulinum Type E Spores in Model Fish Media and in Vacuum-Packaged Hot-Smoked Fish Products

Abstract

Thermal inactivation of nonproteolytic Clostridium botulinum type E spores was investigated in rainbow trout and whitefish media at 75 to 93°C. Lysozyme was applied in the recovery of spores, yielding biphasic thermal destruction curves. Approximately 0.1% of the spores were permeable to lysozyme, showing an increased measured heat resistance. Decimal reduction times for the heat-resistant spore fraction in rainbow trout medium were 255, 98, and 4.2 min at 75, 85, and 93°C, respectively, and those in whitefish medium were 55 and 7.1 min at 81 and 90°C, respectively. The z values were 10.4°C in trout medium and 10.1°C in whitefish medium. Commercial hot-smoking processes employed in five Finnish fish-smoking companies provided reduction in the numbers of spores of nonproteolytic C. botulinum of less than 103 . An inoculated-pack study revealed that a time-temperature combination of 42 min at 85°C (fish surface temperature) with >70% relative humidity (RH) prevented growth from 10 6 spores in vacuum-packaged hot-smoked rainbow trout fillets and whole whitefish stored for 5 weeks at 8°C. In Finland it is recommended that hot-smoked fish be stored at or below 3°C, further extending product safety. However, heating whitefish for 44 min at 85°C with 10% RH resulted in growth and toxicity in 5 weeks at 8°C. Moist heat thus enhanced spore thermal inactivation and is essential to an effective process. The sensory qualities of safely processed and more lightly processed whitefish were similar, while differences between the sensory qualities of safely processed and lightly processes rainbow trout were observed.

Construction of Nontoxigenic Mutants of Nonproteolytic Clostridium botulinum NCTC 11219 by Insertional Mutagenesis and Gene Replacement

“…5). This is in line with previous reports and has been attributed to the existence of a lysozyme-impermeable and -permeable fraction in the spore population (38,39). The decimal reduction times (D values) were calculated only from the log-linear part, corresponding to the presumed lysozyme-permeable fraction.…”

Fish: a potential source of bacterial pathogens for human beings

“…C. botulinum type E is found in marine and lake sediments and in fish intestine; it does not grow or produce toxin in living fish but is carried passively. Commercial hot-smoking processes employed in five fish-smoking companies provided reduction in the numbers of spores of nonproteolytic C. botulinum of less than 10 3 (Lindstrom et al, 2003). Most critical are the hygienic conditions for handling the product a�er smoking.…”

Laboratory Diagnostics of Botulism

“…Group I organisms seem to be more of terrestrial origin and are present in temperate climates, whereas group II strains, particularly type E, are frequently found in aquatic environments in the Northern hemisphere (Table 1). Differences in spore heat resistance and growth temperatures are responsible for the safety risks posed by C. botulinum groups I and II in the food industry; group I spores, which have a high heat resistance (112,138,180,184,192,202), cause problems in canning and home preservation of vegetables and meat, whereas group II spores, with somewhat lower spore heat resistance (135,140,(168)(169)(170), are of great concern in minimally processed packaged foods that have extended shelf lives at refrigerated temperatures (134,167).…”