I am a Ph.D. candidate in Hammes' lab working on the physiology of sour dough lactobacilli. As homofermentative lactic acid bacteria do not produce CO2, yeast must be added to ensure leavening of the dough. As there is no use for NADH, it must be oxidized to NAD again. In the absence of other substrates, acetyl-Phosphate is reduced to ethanol, with two NADH becoming oxidized to HAD in the process. Oxygen is present only in the beginning of the fermentation, and the amounts of oxygen are too low to result in significant amounts of acetic acid, though, in principle, it is possible to increase the acetate content by aeration of dough.
Fructose is present in sucrose and other glucofructans with higher molecular weights.
Thus, the effect of substrates and oxygen on the FQ is nicely explained by the metabolic characteristics of the dominating fermentation organisms. Dear Michael Gaenzele Thank you for sending one of the most gracious letters I have ever received in response to any kind of an inquiry. Since I wrote to Prof. Hammes I have been able to copy a number of articles from English language publications by Drs. Brummer, Spicher, Vogel, and so forth. Unfortunately, some of them have been in non-technical journals and were thus short on details, and even the less technical ones were not as clearly and idiomatically written as your letter.