ABSTRACT
The ingestion of gluten-containing foods can cause wheat-related disorders in up to 15% of wheat consuming populations. Besides the role of gluten, α-amylase/trypsin inhibitors (ATI) have recently been identified as inducers of an innate immune response via toll-like receptor 4 in celiac disease and non-celiac wheat sensitivity. ATI are involved in plant self-defense against insects and possibly in grain development. Notably, they are largely resistant to gastrointestinal proteases and heat, and their inflammatory activity affects not only the intestine, but also peripheral organs. The aim of this study was to understand the changes of ATI throughout the sourdough and yeast-fermented bread-making processes. ATI tetramers were isolated, fluorescein-labelled, and added to a mini-dough bread-making system. When the pH decreased below 4.0 in sourdough fermentation, the ATI tetramers were degraded due to the activation of aspartic proteases, whilst in yeast fermentation, ATI tetramers remained intact. The amylase inhibitory activity after sourdough fermentation decreased significantly, while the concentration of free thiol groups increased. The glutathione reductase activity of Fructilactobacillus sanfranciscensis did not contribute to the reduction of ATI tetramers. Compared to the unfermented wheat, sourdough fermentation was able to decrease the release of pro-inflammatory cytokines monocyte chemoattractant protein-1 (MCP-1) and tumor necrosis factor alpha (TNF-α) in quantitative ATI extracts added to the human monocytic cell line THP-1. The current data suggest that sourdough fermentation can degrade ATI structure and bioactivity, and point to strategies to improve product development for wheat sensitivity patients.
ABSTRACT
Bacillus spp. cause ropy bread spoilage of bread, which is characterized by a rotten fruity odor, followed by discoloration and degradation of the crumb. Bacillus spp. are wheat grain endophytes and form heat resistant endospores, therefore, process hygiene and heating during baking do not prevent ropy spoilage. This study used 8 strains of Bacillus subtilis and Bacillus amyloliquefaciens to determine whether the presence and the copy number of spoVA2mob operon influences survival after baking; in addition, the spoilage phenotype was correlated with the presence of amylolytic enzymes in genomes of Bacillus spp.. The presence and copy number of the spoVA2mob operon had only a minor effect on survival of Bacillus endospores. Strains of B. amyloliquefaciens caused ropy spoilage faster than strains of B. subtilis, this difference correlated to the number and type of extracellular amylases encoded in the genomes of the strains of B. amyloliquefaciens and B. subtilis. The inhibitory effect of sourdough on ropy spoilage was determined by addition of 3-24% sourdough fermented with L. reuteri TMW1.656. Addition of 12% and 24% sourdough, corresponding to a bread pH of 5.93 ± 0.041 and 5.53 ± 0.040, respectively, delayed ropy spoilage for 2 and more than 5 d, respectively. The comparison of addition of 12% sourdough fermented with the reutericyclin producing L. reuteri TMW1.656 and the isogenic reutericyclin-negative strain L. reuteri TMW1.656ΔgtfAΔrtcN demonstrated that reutericyclin produced in sourdough inhibits growth of Bacillus in bread. In conclusion, sourdough inhibits germination of Bacillus spores in bread and the effect of sourdough is enhanced by reutericyclin.
