Discussion
This research has been addressed to exploit an unconventional bacterial association to fulfill the requirement of yeast-free baked goods
consumable by people with adverse responses to the ingestion of
baker's yeast. Due to the similarity between Z. mobilis and S. cerevisiae
fermentation metabolism, this bacterium can be considered an attractive alternative to the yeast in dough leavening.
Leavening trials were carried out using a model dough commonly
employed to test leavening performance of baker's yeast (Burrows
and Harrison, 1959; Havet et al., 2000; Musatti et al., 2015). Trials carried out by mixing only flour and water showed that glucose released
in 6 h leavening is about 2.3 ± 0.3 mg/g dough (i.e. 80 mg/20 g flour);
this sugar can be metabolized by Z. mobilis through the alcoholic fermentation producing only 17–23 mL of CO2. In our trials, 21.5 ±
0.8 mL CO2 were obtained, in good agreement with the corresponding
glucose consumption. As Z. mobilis is not able to utilize maltose, doughs
produced with only this bacterium are poorly leavened: Zymomonas in
this case produces ethanol and CO2 using the small amount of glucose
present or released during leavening by hydrolytic endogenous enzymes in flour (Sprenger, 1996). As expected, CO2 production levels developed in the same conditions by S. cerevisiae, are much higher than
those produced by Z. mobilis. Indeed, when this bacterium has availability of fermentable sugars (i.e. glucose), its leavening performance is
comparable to baker's yeast (Musatti et al., 2015).
The present research illustrates an innovative strategy to improve Z.
mobilis dough leavening ability by exploiting maltose hydrolytic activity
of L. sanfranciscensis. This combinational approach mimics traditional
sourdoughs, in which LAB metabolism favors the set-up of mutualistic