Operator-independent assessment of bread spoilage profiles caused by Bacillaceae reveals a high degree of inter- and intraspecies heterogeneity

Abstract

Ropy bread spoilage caused by aerobic spore-forming bacteria (ASF) is characterized by discoloration, sticky and stringy crumb degradation, and a fruity odor due to the release of volatile organic compounds (VOCs). Previous studies employing model experiments have demonstrated strain-specific spoilage potential. However, to gain a deeper understanding, it is essential to study rope spoilage within baked bread. This study aimed to objectively evaluate the effect of different ASF strains on bread quality. 82 strains were subjected to a comprehensive evaluation, including proteotypic and genotypic fingerprinting, and 13 were selected for further analysis, where ASF endospore-spiked dough samples were baked and incubated. Physical changes in crumb texture, discoloration, and VOC production were quantified using texture analysis, color measurements, and headspace solid-phase microextraction gas chromatography-mass spectrometry. The high intraspecies diversity was reflected in strain-specific variations in rope spoilage profiles. A significant reduction in crumb firmness and increased discoloration, as well as the development of high levels of relative acetoin, were associated with rope spoilage. While color measurements could not detect early-stage spoilage, changes in crumb texture and VOC development were detectable after 24 h of baking. Even low levels of contamination (10^1 spores/g) could cause potential spoilage detectable by texture analysis, although not visible to the naked eye. This study provides an unbiased framework for future research and may help develop early detection tools for improved bread spoilage management.