IngentaConnect Survival and Growth of Psychrotrophic Bacillus cereus in Dry and ...

Abstract:

The potential for growth of enterotoxigenic Bacillus cereus in reconstituted dry foods is a concern, especially when they are consumed by infants or the immunosuppressed. The ability of a four-strain mixture of spores or vegetative cells of psychrotrophic B. cereus to survive in a commercial, dry infant rice cereal as affected by water activity (a_w; 0.27 to 0.28, 0.52 to 0.55, and 0.75 to 0.78), pH (5.6 and 6.7), and temperature (5, 25, 35, and 45°C) was investigated. The rate of death of vegetative cells in dry cereal stored for 36 weeks was not affected by a_w or pH. Death of spores in cereal stored at 45°C for up to 48 weeks was enhanced at a_w 0.78 but was unaffected by pH; loss of viability at 5, 25, and 35°C was largely unaffected by differences in a_w. The effect of temperature (8, 15, 21, and 30°C) on outgrowth of spores of B. cereus inoculated at three levels (0.14, 14, and 133 CFU/g, dry weight basis) into cereal reconstituted with apple juice and commercial pasteurized milk (2% fat) was also studied. Outgrowth of spores did not occur in cereal reconstituted with apple juice. Cereal reconstituted with milk and inoculated with 0.14, 14, and 133 spores per g contained >3 log CFU/g within 24, 9, and 6 h, respectively, at 21°C. Populations in cereal reconstituted with milk and inoculated with 133CFU of B. cereus spores per g reached 7.11, 7.72, and 7.40 log CFU/g within 12, 48, and 72 h when stored at 30, 21, and 15°C, respectively. The organism grew in cereal reconstituted with milk and held at 8°C for 72 h; however, enterotoxin was not detected. In reconstituted cereal inoculated with 133 spores per g, enterotoxin was detected (detection limit 16 ng/g) after 24, 48, and 72 h at 30, 21, and 15°C, respectively, when the population of B. cereus reached > 7 log CFU/g. It is recommended that reconstituted infant foods be either consumed immediately or held at ≤ 8°C and consumed within 48 h after preparation.

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Survival and Growth of Psychrotrophic Bacillus cereus in Dry and Reconstituted Infant Rice Cereal