Fig 1.
Glycerol biosynthesis and CO2 production.
Glycerol biosynthesis from dihydroxyacetone phosphate is a two-step process. The first step which is catalyzed by the Gpd enzyme, is rate limiting for the production of glycerol. Overproduction of glycerol and carbon flux towards glycerol production is linked with decreased CO2 production from fermented sugar.
Fig 2.
GPD1 tunes intracellular glycerol concentration.
We measured the intracellular glycerol level before exposure to the high osmolarity condition (before inoculation into dough). Deletion (A) and overexpression (B) of GPD1 in both yeast backgrounds results in respectively decreased (p < 0.05 for bakery strain) and increased (p< 0.05 for both strains) intracellular glycerol level. The control strain used in panel B is a wild-type (WT) strain transformed with the same overexpression plasmid that did not contain the GPD gene (“empty vector control”). Bar graphs show the average of the repeats and error bars represent the standard deviation from the mean. Bar graphs with asterisk are significantly different from their corresponding control.
Fig 3.
Glycerol production is crucial for efficient dough fermentation.
Δgpd1 mutants show impaired dough fermentation (p < 0.05) (A) even though these mutants show a similar fermentation profile as the respective wild-type strains when salt-free dough is used (B). Bar graphs show the average of the repeats and error bars represent the standard deviation from the mean. Bar graphs with asterisk are significantly different from their corresponding control.
Fig 4.
GPD1 overexpression increases the fermentation capacity of the laboratory strain in high-sugar dough.
(A) In low-sugar dough, increased glycerol production does not influence the fermentation capacity, (B) but in higher osmotic pressure, 50% improvement in one of the backgrounds was observed (p < 0.05). Bar graphs show the average of the repeats and error bars represent the standard deviation from the mean. The bar graph with asterisk is significantly different from its corresponding control. (C) CO2 measurement profile during fermentation of high-sugar dough (18%) recorded by Risograph shows that this improvement in the fermentation capacity of laboratory strain is due to the shorter lag of the mutant compared to the control and the swift start of fermentation.
Fig 5.
Fermenting with the strain with higher glycerol production level leads to stronger dough structure.
(A) GPD1 overexpression results in a 30% (bakery strain, left) or 100% (laboratory strain, right) increase in glycerol levels in dough. Error bars represent the standard deviation from the mean (average of the repeats). (B) Rheofermentometer analysis indicates that the dough shows better gas retention once fermented with the GPD1-overexpressing mutant. The arrows represent the maximum height of dough fermented with different strain or mutants. The bigger maximum height and slower decrease of the height is associated with better gas retention in dough. The difference is more pronounced in the laboratory strain (right).