I am conducting fermentation experiments with Hydrogenophaga psuedoflava whereby sucrose is the main substrate. I tried adding up to 6.8 g/L sodium formate as a co-substrate and noticed that, at the higher concentrations of sodium formate, pH actually increases rather than decreasing over time as was the case normally when fermenting sucrose only (up to 10 g/L). Why is that?
Hello, the formate is fermented to methane and carbon dioxide as shown: 4HCOOH - CH4 + 3CO2 + 2H20. If the pH of the fermentation medium is maintained in pH range (about 8.0 to 8.5), the stoichiometry of the equation is obeyed, but the continued fermentation of sodium formate can increase in pH due to the accumulation of sodium carbonate in fermentation media.
Since E.Coli is active at lower pH -https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/mixed-acid-fermentation
The sodium formate solution has a high concentration of sodium ions and formate ions and a small concentration of formic acid and hydroxide ions. ... This removes some hydronium ion from solution, increasing the pH. https://www.chm.uri.edu/weuler/chm112/lectures/lecture17.html
Check https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/mixed-acid-fermentation
Acetate is always produced as a volatile fatty acid (VFA) product. Excess carbon and electrons are released as carbon-dioxide and hydrogen respectively. This therefore increases the pH.
Thank you, everyone, for your input, especially Karen A. Darbinyan and Chinaza Godswill Awuchi
I ran my samples in HPLC finally and noticed that the formate, CHO2–(aq), is being consumed overtime by my strain. Given how sodium formate disassociates in water, NaCHO2(aq) → Na+(aq) + CHO2–(aq), I expect that this results in the accumulation of Na+ in the medium. On the other hand, the subsequent hydrolysis, CHO2–(aq) + H2O(l) ⇋ HCHO2(aq) + OH–(aq), is taking place at a slower rate since CHO2–(aq) is being consumed. How are any of these two mechanisms increasing pH? Moreover, Karen A. Darbinyan, I am not sure how this is leading to the accumulation of sodium carbonate. Can you give more details please?
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