Survival and growth of Bacillus cereus in Egyptian bread and its effect on bread staling.

Abstract

Bread was made from dough previously inoculated with spores of three Bacillus cereus strains at different inoculation levels. Counts of survivors and bread staling were determined in bread during storage at 25 degrees C. The total aerobic bacteria, sporeformer and B. cereus counts in seven different wheat flours were 3.0 x 10(6) to 9.1 x 10(7), 3.2 x 10(5) to 1.5 x 10(6) and 50-100 colony forming units (CFU/g). About one in a thousand bacteria were found to survive baking. On the other hand, no multiplication took place, however, until the bread had been stored for more than 3 days. Also, survival and multiplication of B. cereus spores was shown to depend on the kind of strains and type of bread. The addition of B. cereus strains to the dough gave bread with higher freshness than the control sample. This was quite noticeable in inoculated pan bread during storage. It is possible to conclude from the results that B. cereus survive the baking process particularly if original contamination is high. Also increasing the freshness of the bread does not necessarily mean better ingredient and processing conditions.