glucose is still present (Fig. 4), indicate that Z. mobilis metabolism is negatively affected. HPLC analysis revealed that maltose concentration in
dough is lower than in doughs leavened by L. sanfranciscensis alone. In
the last leavening phase, maltose concentration increased, perhaps indicating a decrease of maltose hydrolytic activity by the lactic acid bacterium (Fig. 4).
When L. sanfranciscensis is present at low concentration (i.e. Lb:Zym
1:10), CO2 productivity was lower if compared to the other associations.
Nevertheless, time course of CO2 production did not show an evident
decrease at the end of incubation (Table 2) and indeed dough pH is
higher than 4 (Table 3). These data indicate that glucose released by L.
sanfranciscensis is probably not enough to support Z. mobilis fermentative metabolism, that proceeds slowly but almost constantly (Fig. 3).
On the overall, to find out the best microbial association between
these two bacteria, the following conditions have to be fulfilled: i) glucose release by L. sanfranciscensis should be consistent to achieve an
efficient Z. mobilis dough leavening, ii) dough acidity should not limit
Z. mobilis fermentative metabolism, even if dough acidity is a positive
factor to limit microbial growth of spoiling microbiota, thus increasing
product shelf life (Corsetti and Settanni, 2007).
On the basis of the obtained results, we can conclude that it is possible to associate L. sanfranciscensis with Z. mobilis to obtain an efficient
dough leavening, by-passing Z. mobilis incapacity to metabolize maltose.
The effect of the strain is another parameter to be investigated, as the intraspecific diversity may affect the relationships that are established in
mutualistic microbial associations (Picozzi et al., 2010). Further research
trials are necessary to better understand which kind of metabolic interactions these two bacteria are able to establish and in which combination they should be used in the commonly applied dough
formulations, to develop yeast-free baked products. Focus has also to
be paid on the stability of this new bacterial association, in particular
when dealing with traditional sourdough back-sloping