Formation of taste-active metabolites in sourdough fermentation and the fermentation of plant-based cheese analogues
Creators: Xie, Jin
Publisher: name: University of Alberta Library
Year: 2024

<p>Fermentation is an oldest and effective method to generate taste-active compounds which contribute to food taste. The aim of this PhD dissertation was to investigate the synthetic mechanism of taste-active γ-glutamyl dipeptides during sourdough fermentation and the fermentation of plant-based cheese analogues, and their effect on taste of foods.<br>
Kokumi γ-glutamyl dipeptides accumulate in sourdoughs. To understand the role of γ-glutamyl-cysteine ligases (Gcls) from lactobacilli in the formation of taste-active γ-glutamyl dipeptides in sourdough or sourdough bread, three Gcls from strains of Lm. reuteri, designated as Gcl1, Gcl2 and Gcl3, were characterized. In addition, sourdoughs were fermented with strains of Lm. reuteri or its Gcl-deficient mutant strains, subsequently used for the production of sourdough breads. The results showed that in enzymatic reaction with an individual amino acid, Gcl3 exhibits the broadest substrate specificity among three Gcls and all three Gcls were inactive to Val, Asp and His. All three Gcls of Lm. reuteri with a mixture of amino acids were most active to Cys among 12 amino acids. Gcl1 exhibited a stronger activity with hydrophobic amino acids Ile, Leu, and Phe when compared to Gcl2 and Gcl3. In sourdough fermentation, the accumulation of kokumi γ-glutamyl dipeptides was attributed to the combined activity of cereal enzymes, Gcls of lactobacilli and other microbial enzymes in lactobacilli. Although several γ-glutamyl dipeptides were synthesized during sourdough fermentation, baking processing strongly influenced the concentrations of γ-glutamyl dipeptides in bread. The effect of γ-glutamyl dipeptides in taste of bread remain to be investigated further. <br>
Consumer demand for plant-based cheese analogues is increasing but challenges remain to improve the flavor and quality. The study described in thesis investigated microbiological and physicochemical impacts of seed germination and fermentation with Bacillus spp. on proteolysis in plant-based cheese analogues and the contribution of adjunct cultures on the accumulation of kokumi γ-glutamyl dipeptides in the fermentation of plant cheese analogues. Bacilli but not seed germination enhanced proteolysis of plant-based cheese analogues and release of glutamate during ripening. Lp. plantarum and Lc. lactis served as starter cultures for plant milk acidification; Lv. hammesii, Ff. milii, or Lt. buchneri was assessed as an adjunct culture for the ripening of plant cheese analogues. During ripening of plant-based cheese analogues, Lc. lactis and Lp. plantarum were inactivated. Cell counts of Lv. hammesii remained stable over 45 d of ripening while Ff. milii and Lt. buchneri grew slowly.  The combined activity of seed germination, Bacillus spp., and adjunct culture lactobacilli contributed to the synthesis of kokumi γ-glutamyl dipeptides in plant-based cheese analogues. <br>
Overall, this research revealed the synthetic mechanism of taste-active γ-glutamyl dipeptides in sourdough fermentation and the fermentation of plant cheese analogues, providing insights into the control of formation of taste-active compounds in food fermentations. </p>