Abstract
Cold-tolerant, neurotoxigenic, endospore forming Clostridium (C.) botulinum type E belongs to the non-proteolytic physiological C. botulinum group II, is primarily associated with aquatic environments, and presents a safety risk for seafood. High pressure thermal (HPT) processing exploiting the synergistic effect of pressure and temperature can be used to inactivate bacterial endospores. We investigated the inactivation of C. botulinum type E spores by (near) isothermal HPT treatments at 300–1200 MPa at 30–75°C for 1 s to 10 min. The occurrence of heat and lysozyme susceptible spore fractions after such treatments was determined. The experimental data were modeled to obtain kinetic parameters and represented graphically by isoeffect lines. In contrast to findings for spores of other species and within the range of treatment parameters applied, zones of spore stabilization (lower inactivation than heat treatments alone), large heat susceptible (HPT-induced germinated) or lysozyme-dependently germinable (damaged coat layer) spore fractions were not detected. Inactivation followed first order kinetics. Dipicolinic acid release kinetics allowed for insights into possible inactivation mechanisms suggesting a (poorly effective) physiologic-like (similar to nutrient-induced) germination at ≤450 MPa/≤45°C and non-physiological germination at >500 MPa/>60–70°C. Results of this study support the existence of some commonalities in the HPT inactivation mechanism of C. botulinum type E spores and Bacillus spores although both organisms have significantly different HPT resistance properties. The information presented here contributes to closing the gap in knowledge regarding the HPT inactivation of spore formers relevant to food safety and may help industrial implementation of HPT processing. The markedly lower HPT resistance of C. botulinum type E spores compared with the resistance of spores from other C. botulinum types could allow for the implementation of milder processes without endangering food safety.
Highlights
Clostridium botulinum type E belongs to the non-proteolytic C. botulinum group II, one of four phylogenetically distinct lineages comprising several different species (Collins and East, 1998)
Spore Inactivation in Different High Pressure Units To be able to compare the results from experiments under isothermal–isobaric conditions conducted in the high pressure units U111 and FBG 5620 and the results obtained for the High pressure thermal (HPT)-mediated release of Dipicolinic Acid (DPA) from spores conducted in unit TMW-RB, it is essential that treatments with identical target parameters (p/T/t) in the different units exert comparable effects on spores
Commonalties and significant differences exist between the HPT-mediated inactivation of C. botulinum type E and other endospores
Summary
Clostridium botulinum type E belongs to the non-proteolytic C. botulinum group II, one of four phylogenetically distinct lineages comprising several different species (Collins and East, 1998). Endospores of this organism are primarily associated with aquatic environments including sea and fresh water sediments in temperate regions of the northern hemisphere (Hielm et al, 1998a,b). Its spores are more susceptible to inactivation by heat than those from other C. botulinum types, they can survive mild heat treatments such as traditional hot-smoking processes, where the internal product temperature typically peaks at 65– 85◦C (Hyytia et al, 1998; Hyytiä-Trees, 1999). The fact that C. botulinum type E is able to grow and form toxin at temperatures as low as 3◦C (Peck, 2006) increases the hazards arising from this organism, especially for sous-vide products and other refrigerated processed foods of extended durability (REPFEDs) where food safety relies on mild processing conditions and refrigerated storage (Lund and Peck, 1994)
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