Initial challenge studies with spores of proteolytic Clostridium botulinum types A and B (~104 spores/g) showed that while air- and gas-packaged English-style crumpets (aw 0.990) and pizza crust (aw 0.960) were toxic after 42-days storage at ambient temperature (25°C), no neurotoxin was detected in bagels (a w 0.944). Further challenge studies with similarly packaged crumpets inoculated with C. botulinum (~102 spores/g), pre- or post-baking, demonstrated that all crumpets were toxic within 4 to 6 days at 25°C and that toxigenesis preceded spoilage. Furthermore, reformulating crumpets to pH 8.3 and packaging in 100% CO2 had little effect in delaying the growth of C. botulinum compared to crumpets formulated to pH 6.5 and packaged in 60% CO2. / Subsequent studies were directed at determining the levels of additional barriers that could be used to ensure the safety of high-moisture MAP crumpets. While ethanol vapour proved to be an effective additional barrier in crumpets (100-g, [aw 0.990, pH 6.5]) challenged with ~102 spores/g of C. botulinum, spoilage preceded toxigenesis due to absorption of ethanol from the package headspace by crumpets. Modelling studies in Trypticase Peptone Glucose Yeast (TPGY) broth confirmed the anti-botulinal nature of ethanol and showed that a level of ~4% (vol/vol) could be used for complete inhibition of this pathogen, depending on the aw and pH of the growth medium. However, while ethanol vapour could be used to inhibit the growth of C. botulinum in high-moisture crumpets, its anti-botulinal efficacy was influenced by the method of crumpet leavening (yeast v chemical). / Preliminary studies were also done to assess the potential of mastic oil, a novel inhibitor, against C. botulinum. While direct and indirect application of ethanolic extracts of mastic oil inhibited the growth of C. botulinum in vivo, they failed to do so in crumpets.

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