Comparative analysis of the role of Bacillus species as food fermenting and food spoilage organisms

• Author / Creator

  Li,Zhen

• Bacillus species are fermenters in some food fermentation but spoilage organisms in other food products. For instance, bacilli and fungi are the predominant organisms in daqu fermentation. The antifungal lipopeptides produced by bacilli, including surfactins, fengycins and iturins, may impact fungal growth during daqu fermentation, thereby influencing the microbial community. The interaction between Bacillus lipopeptides and fungi in daqu is unclear. Therefore, a simulated model of daqu was created to investigate the role of antifungal lipopeptides in situ. The results showed that iturin A displayed the strongest antifungal activities in vitro. B. velezensis FUA2155 exhibit higher antifungal activity than two strains of B. amyloliquefaciens in the daqu model, due to the production of iturin A. Additionally, hydrolytic enzymes produced by Bacillus spp. can cause ropy bread spoilage, which leads to economic losses in bakeries. Bacillus spp. are wheat grain endophytes and form heat resistant endospores, consequently, process hygiene and heating during baking are insufficient to prevent ropy spoilage. Therefore, to reduce the negative impact of Bacillus and increase the shelf life of bread, sourdough was investigated as a biopreservative. The results indicated more than 2 d delay of spoilage with an addition of 12 % sourdough fermented by lactic acid bacteria. Bread with reutericyclin exhibited a bactericidal mode of action against strains of Bacillus.
  In food industries, the high thermal loads that are required for inactivation of Bacillus spores can result in significant loss of food quality. Pressure-assisted thermal sterilization is a promising approach for spore inactivation without the need for high thermal stress. Nevertheless, the pressure resistance of Bacillus spores varies greatly. The spoVA2mob operon increases heat resistance of spores and multiple copies of the operon further increases the heat resistance. However, the role of spoVA2mob operon in pressure resistance is not well explored. In this study, the pressure resistance of 17 strains of Bacillus were correlated with the copy number of the spoVA2mob operon. To study the role of spoVA2mob operon in pressure resistance and spore germination triggered by different germinants, an isogenic mutant strain of Bacillus subtilis 168 with insertion of spoVA2mob operon was created. The spoVA2mob operon increased pressure resistance and decreased pressure induced spore germination significantly.
  Overall, this research provides insights into the interaction of Bacillus and other microorganisms, such as fungi and lactic acid bacteria in food fermentations, to better understand the role of Bacillus as fermenting or food spoilage organisms.

• Subjects / Keywords

  • Bacillus
  • Antifungal lipopeptides
  • Food fermentation
  • spoVA2mob
  • Ropy bread
  • High pressure

• Graduation date

  Fall 2022

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-5a2p-0j27

• License

  This thesis is made available by the University of Alberta Library with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.