Co-fermentation is a process in which two or more substances are fermented together to produce a desired product. In the context of sugar and glycerol mixture, co-fermentation involves the simultaneous fermentation of both sugars to produce PDO (1,3-propanediol).
The process of co-fermentation begins with the introduction of the sugar and glycerol mixture to a fermentation vessel, along with the necessary microorganisms or enzymes. These microorganisms or enzymes play a crucial role in converting the sugars into PDO.
One of the key enzymes involved in the co-fermentation process is glycerol dehydrogenase (GDH), which catalyzes the conversion of glycerol to dihydroxyacetone (DHA). GDH is typically produced by certain microorganisms such as bacteria. Another enzyme, glycerol dehydratase (GDHt), then converts DHA into 3-hydroxypropionaldehyde (3-HPA).
Next, 3-HPA is converted into PDO by the enzyme PDO reductase (PDOR). PDOR is responsible for the reduction of 3-HPA to PDO, which is the desired end product of the co-fermentation process. the enzyme dihydroxyacetone kinase (DHAK) converts DHA into ATP, which provides energy for the overall fermentation process.
However, in the presence of glucose, the synthesis of these enzymes is typically repressed, particularly during the initial fermentation phase. Glucose is a preferred carbon source for many microorganisms, and they tend to consume it first before utilizing other sugars or substrates. As a result, the production of PDO is delayed or inhibited until glucose is depleted.
During the initial phase of co-fermentation, glucose is the main sugar consumed by the microorganisms. As glucose levels decrease, the microorganisms switch to utilizing other sugars present in the mixture, such as glycerol. This shift in sugar utilization triggers the synthesis and activation of the enzymes responsible for the conversion of glycerol to PDO.
In my experience as a brewer, I have encountered situations where the co-fermentation process was affected by the presence of glucose. It is crucial to monitor glucose levels and ensure that it is consumed before expecting significant PDO production. By carefully managing the fermentation conditions and providing a suitable environment for the growth and activity of the microorganisms involved, it is possible to optimize the co-fermentation process and enhance PDO production.
To summarize, co-fermentation of a sugar and glycerol mixture involves the simultaneous fermentation of both sugars to produce PDO. The synthesis of enzymes responsible for the conversion of glycerol to PDO is usually repressed in the presence of glucose, leading to a delay or inhibition of PDO production. However, as glucose levels decrease, the microorganisms shift their sugar utilization and activate the enzymes, allowing for the conversion of glycerol to PDO. Proper monitoring and management of fermentation conditions are necessary to optimize the co-fermentation process and achieve the desired PDO production.