Conversion of Protein to Bioactive Peptides in Sourdough Fermentation

  • Author / Creator
    Zhao, Jing
  • Sourdough fermentation can generate various peptides and amino acids to improve bread quality, such as taste, flavor and texture. The aim of this PhD dissertation was to investigate the synthesis mechanisms of bioactive and taste active peptides or amino acids during fermentation and their effect on food quality. To understand the effect of glutamate on bread taste, sourdough was fermented with GABA-accumulating L. reuteri 100-23 and the glutamate-accumulating mutant L. reuteri 100-23ΔgadB. The difference of glutamate contents between sourdough breads was equal to its taste threshold (0.03%). Nevertheless, the taste difference between bread fermented with L. reuteri 100-23 and 100-23Δgadwas attributed to umami. Besides, a consumer panel (n=40) ranked the salty taste of L. reuteri sourdough bread with 1.0% NaCl equal to that of the reference bread with 1.5% NaCl but higher than that of the reference bread with 1.0% NaCl. These results confirmed the umami taste of glutamate in sourdough bread and the taste enhancer activity of glutamate in bread. A series of -glutamyl dipeptides with kokumi taste activity was first found in sourdough. Proteolysis and strain specificity are the key factors to generate dipeptides. Amino acids model of Lactobacillus confirmed the contribution of microorganisms in the generation of γ-glutamyl dipeptides, even though the specific metabolism pathway is still unclear. At subthreshold of -glutamyl dipeptides, the sourdough bread with -glutamyl dipeptides ranked higher in salty taste than regular bread and type I sourdough bread. Moreover, the significant difference in salty taste between sourdough breads fermented with L. reuteri LTH5448 and L. reuteri 100-23 is attributed to the significant difference in the level of -glutamyl dipeptides. This result indicated the contribution of -glutamyl dipeptides to the taste of bread. The use of sourdough fermented with glutamate and kokumi peptide accumulating lactobacilli allowed reduction of NaCl without any adverse effect on the other taste or quality attributes. The ACE-inhibitory tripeptides have been found during sourdough fermentation. The bread-making steps, including kneading, proofing and baking affect the stability of peptides. The levels of peptides after different thermal treatments, including steamed bread, baked bread and soda crackers, were compared. The X-PP was the most stable peptides during dough stage but decreased during baking whereas other ACE tripeptides remained stable during baking but decreased during the dough stage. The cumulative concentrations of 8 ACE-inhibitory peptides in steamed bread and baked bread likely meet in vivo active concentrations. In conclusion, through the combination of glutamate, kokumi peptides, ACE-inhibitory peptides as well as GABA, new functional bread can be produced with low sodium and bioactive compounds without adverse effects on taste or other quality attributes.

  • Subjects / Keywords
  • Graduation date
    Spring 2016
  • 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.