Metabolism of lactic acid bacteria in wheat sourdough and bread quality

  • Author / Creator
    Zhang, Chonggang
  • Study on metabolism of lactic acid bacteria in wheat sourdough can improve bread quality such as bread flavour, texture and shelf life. This dissertation focused on several metabolic pathways in Lactobacillus strains on both biochemical and genetic level to fulfill three objectives. The first objective was to produce bread preservative propionate from lactate by cometabolism of Lactobacillus buchneri and Lactobacillus diolivorans to extend bread shelf life. The results showed that propionate was formed in cofermentation. Bread containing 20% sourdough from coferementation effectively inhibited growth of three of the four selected moulds for more than 12 days compared to traditional sourdough. The use of 10% experimental sourdough deferred growth of two molds by one day. The second objective was to characterize the metabolism of α-ketoglutarate (α-KG) in sourdough strains. Alpha-KG is an important amino group acceptor for flavour production during sourdough fermentation, however, knowledge on metabolism of α-KG in sourdough strains is lacking. Study of metabolism of α-KG in Lactobacillus sanfranciscensis and Lactobacillus reuteri showed that L. sanfranciscensis and L. reuteri utilized α-KG as electron acceptor, which was converted to 2-hydroxyglutarate in both media and wheat sourdough. The presence of phenylalanine and citrate in addition to α-KG partially redirected the use of α-KG from electron acceptor to amino group acceptor. The third objective was to compare the acid resistance pathways in L. reuteri 100-23. Inducible gene expressions for acid resistance are important survival strategy for Lactobacillus. Genes encoding three glutaminases in L. reuteri 100-23 were studied and compared with adi and gadB to find out the responsible acid resistance pathway under different acidic conditions. Under pH 3.5, ADI pathway is effective in acid resistance. Expression of gls3 was the highest during acid resistance among the three glutaminase genes. Analysis of gene expression in ∆gadB and ∆ gls3 strains showed that deletion of gadB resulted in over- expression of adi and gls3, whereas deletion of gls3 showed over-expression of gls1, gls2 and gadB compared to wild type strains. Gene expression in wheat sourdough showed comparable over-expression of gls3 and gadB.

  • Subjects / Keywords
  • Graduation date
    Fall 2011
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries 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.
  • Language
  • Institution
    University of Alberta
  • Degree level
  • Department
  • Supervisor / co-supervisor and their department(s)
  • Examining committee members and their departments
    • Dr. Ismail Fliss, Département des sciences des aliments et de nutrition, Université Laval
    • Dr. Karen Madsen, Department of Medicine
    • Dr. Thava Vasanthan, Department of Agricultural, Food and Nutritional Science
    • Dr. Michael Gänzle, Department of Agricultural, Food and Nutritional Science
    • Dr. Lynn McMullen, Department of Agricultural, Food and Nutritional Science
    • Dr. Lingyun Chen, Department of Agricultural, Food and Nutritional Science