Detection of rope spoilage in bread caused by Bacillus species

Abstract

Rope spoilage of bread by eight Bacillus isolates obtained from a bakery environment was examined via direct inoculation of slices of bread with bacterial culture. The three types of loaf examined were two soft grain varieties, one containing vinegar and the other containing calcium propionate as the preservative agent, and a white variety containing calcium propionate. Differences in rope production caused by batch variation were studied by comparing seven loaves of each type of bread. Not all isolates were capable of causing extensive rope, but isolates of Bacillus subtilis, B. licheniformis, B. megaterium and B. pumilus were able to produce such spoilage. Limited rope was also caused by pre-existing Bacillus species within the loaves. The amount of rope production by an isolate was not constant on all loaf types or even between different batches of the same variety, indicating that approaches that rely on direct inoculation of loaves with culture are not applicable for assessing the rope-inducing potential of Bacillus isolates. However, it was clear from this study that vinegar in soft grain loaves was more effective than calcium propionate at inhibiting rope.