Team:BHSF/Description

Attributions

Our team members all love baking. We often bake at home, especially during the pandemic when we had no where to buy bread. Besides, baking at home is much safer.

However, when baking at home, as students, we often go studying during the process of fermentation and unable to bake the dough(kill the yeast) on time, leaving the bread over-fermented (we will explain this term in the following paragraphs). When we exchanged with other people who also bake at home, we discovered that many others are troubled by the same problem of not being able to terminate fermentation in time, what’s more, due to the lack of experience, some people had no idea of the appropriate time to ferment.

All these problems lead to over-fermentation, making the bread hard like a stone, with a terrible smell, and greatly hurts the confidence of the bakers.

Fermentation (also called proofing) is the most important process in baking, the principle of this process is the respiration of yeasts and other microbes, during which they consume simple sugars generated by amylase in the flour and produce Carbon dioxides.

The formula of fermentation is:
C₆H₁₂O₆ + 6H₂O + 6O₂ --→ 6CO₂ + 12H₂O + ATP

And some organic acid will be produced as the by-product of fermentation.[1]

Carbon dioxide lifts up the gluten in the dough and allows the bread to leaven, therefore gives the bread its structure, dough volume, lightness and touch.
The principle of baking is also shown in the picture below.

Too much fermentation can result in excessive production of Carbon dioxide and will destroy gluten [2](structure) of bread, making the dough so weak that it cannot shape properly, not to mention that it probably won’t rise very well either, that’s why sometimes we baked ‘stones’ instead of fluffy bread[3]. What’s more, overfermentation gives your dough too much by-product, making it too acidic, these acids will impede crust color development. Last but not the least, if the oxygen left in the dough is insufficient, the yeast will begin anaerobic aspiration and produce alcohol which makes the bread smell weird.[4]

Therefore, we came up with the idea of modifying the genes in the auxotrophic baking yeast and designed a circuit based on toggle switch.

Before we add the inducer galactose, the switch is kept at “off” state, where the gene (in yellow) of an inhibitor protein, along with one that complements the auxotroph, get to express, while expression of the other inhibitor (in red) is repressed nearly to the full extent.

After galactose is added, the expression of recombinase (in green) is activated, which in subsequently initiate the expression of the gene in red by flipping the reversed promoter in front of it, the over-expression of the red inhibitor triggers the switch to be turned on, and the expression of the other inhibitor (in yellow) is rapidly shut down, leading to a drop in its concentration, and the following gene that complements the auxotroph stops expressing. The yeast then goes into dormancy, so that we can terminate fermentation over a certain period of time.

Note:
1.Fermentation also produces other compounds such as acid，which gives the dough its unique flavor and strength (acids help condition the gluten network).
2.Gluten is the protein in the flour, which mainly forms the structure of bread.
3.The influence of fermentation on texture is extremely obvious in soft rolls, this process determines whether its fluffy or not.
4.By over-fermentation, we are saying producing too much ethanol(alcohol) and acid, moderate amount of them are necessary for some types of bread, but too much them is always not a good thing, that’s what our project is for.

Reference and resources

Team:BHSF/Description

Reference and resources

-Baking

-Design

-Modeling

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