Aerobic spore-forming bacteria associated with ropy bread: Identification, characterization and spoilage potential assessment

• Published in: International journal of food microbiology 2024-06, Vol.418, p.110730-110730, Article 110730
• Main Authors: Pacher, Nicola, Burtscher, Johanna, Bender, Denisse, Fieseler, Lars, Domig, Konrad J.
• Format: Article
• Language: English
• Subjects: Bacillus spp; Bacteria, Aerobic - classification; Bacteria, Aerobic - genetics; Bacteria, Aerobic - growth & development; Bacteria, Aerobic - isolation & purification; Bread; Bread - microbiology; Colorimetric measurements; Food Contamination - analysis; Food Microbiology; RNA, Ribosomal, 16S - genetics; Rope spoilage; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Spores, Bacterial - growth & development; Virulence Factors - genetics
• ISSN: 0168-1605; 1879-3460
• DOI: 10.1016/j.ijfoodmicro.2024.110730

Aerobic spore-forming (ASF) bacteria have been reported to cause ropiness in bread. Sticky and stringy degradation, discoloration, and an odor reminiscent of rotting fruit are typical characteristics of ropy bread spoilage. In addition to economic losses, ropy bread spoilage may lead to health risks, as virulent strains of ASF bacteria are not uncommon. However, the lack of systematic approaches to quantify physicochemical spoilage characteristics makes it extremely difficult to assess rope formation in bread. To address this problem, the aim of this study was to identify, characterize and objectively assess the spoilage potential of ASF bacteria associated with ropy bread. Hence, a set of 82 ASF bacteria, including isolates from raw materials and bakery environments as well as strains from international culture collections, were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and their species identity confirmed by 16S rRNA and gyrA or panC gene sequencing. A standardized approach supported by objective colorimetric measurements was developed to assess the rope-inducing potential (RIP) of a strain by inoculating autoclaved bread slices with bacterial spores. In addition, the presence of potential virulence factors such as swarming motility or hemolysis was investigated. This study adds B. velezensis, B. inaquosorum and B. spizizenii to the species potentially implicated of causing ropy bread spoilage. Most importantly, this study introduces a standardized classification protocol for assessing the RIP of a bacterial strain. Colorimetric measurements are used to objectively quantify the degree of breadcrumb discoloration. Furthermore, our results indicate that strains capable of inducing rope spoilage in bread often exhibit swarming motility and virulence factors such as hemolysis, raising important food quality considerations. •New classification protocol for quantification of the rope inducing potential.•B. velezensis, B. inaquosorum, B. spizizenii added to species related to ropy bread.•Colorimetric method establishes ΔE* > 10 cut-off for potential spoilage strains.