Effect of pH and CO2 on growth and toxin production by Clostridium botulinum in English-Style crumpets packaged under modified atmospheres

The effect of pH and CO2 on both growth of and toxin production by Clostrid ium botulinum in English-style crumpets, packaged under modified atmosphere s was investigated using a 2 x 2 factorial experiment. English-style crumpe ts (water activity, 0.990: pH 6.5 and 8.3) were inoculated with C. botulinu m spores types A and proteolytic B (500 spores/g), packaged in either 60% C O2 (balance N-2) or 100% CO2, stored at ambient temperature (25 degrees C), and monitored daily for toxicity. Toxin was detected after 4 days in crump ets packaged in 60% CO2, irrespective of initial product pH. Toxin producti on was delayed 1.5 to 3 days in crumpets packaged under 100% CO2. Analysis of variance indicated a significant interaction effect of pH and %CO2 on ti me of earliest toxin detection. Delay of toxin production was greatest for high pH (8.3) crumpets. All products were organoleptically acceptable at th e time of toxigenesis, and therefore, high moisture-high pH bakery products , if contaminated with spores of C. botulinum, could become hazardous if pa ckaged in atmospheres containing CO2.