pH increasing problem of yeast fermentation (under aerobic condition) - (Dec/14/2011 )

Dear all,

Recently I did consuming experiments with two monosaccharides (glucose and galactose) by Kluyveromyces marxianus (yeast) in the fermentor. The initial pH of medium is 7.0. I think it is normal that the pH dropped down to 6.5 after overnight incubation while stirring but without ventilation.
But I also found that when the reaction is stirring with ventilation, the pH increases immediately to 7.99 after half a hour. I don’t know what is the reason? Could you give me some suggestions?
Thanks in advance!

Biogareth

Still waiting for your suggestions!

Hola,at least in sacharomyces, you don´t need close aireation to have fermentation only adding sugars (glucose) above 1g/l yeast will partially oxide the sugar giving ethanol (crabtree efect) and pH lows a bit less than in respiration. If the pH increases could be due to deamination of amino acids, but it occurs when medium haven´t sugar or by the effect of hign levels of dissolved oxigen when optical density is very low at the beginning of culture, I believe. If decreasing air/oxigen flow ,pH decrease it would be the reason if no, I haven´t more opinion to give you but I will think. Buena suerte