## 4 Discussion
### Strategies to Improve Gluten-Free Dough Rheology and Bread Characteristics
#### 4.1.8 Sourdough Fermentation  
Several authors have investigated the effects of sourdough fermentation on gluten-free dough rheology and bread characteristics. For example, [PERSON] and [PERSON] (2015) [13] highlighted that sourdough fermentation positively influenced all aspects of bread quality: texture, aroma, nutritional properties, and shelf life. However, improvement was strictly dependent on the used microbiota. Moreover, the possibility of obtaining natural products with a reduced use of additives or even clean labels is appealing. The acidification of gluten-free doughs by sourdough fermentation can partially replace the function of gluten, and enhance polysaccharide swelling [14]. In particular, [PERSON] and [PERSON] (2008) [15] highlighted that sourdough fermentation increased dough elasticity over the initial 24 h of fermentation, and delayed the onset of bread staling. Furthermore, [PERSON] and [PERSON] (2012) [17] highlighted that it increased loaf specific volume, and improved the texture of bread produced with oat flour.  
The findings outlined above are supported by other work [53]. The latter study investigated the effect of sourdough made from combinations of four _Lactobacillus_ spp. on the physicochemical properties, consumer acceptability, and shelf life of formulations made with pearl millet flour. The authors found that sourdough fermentation increased the elasticity, and reduced the stiffness of doughs [53]. Doughs fermented with _L. brevis_ had the greatest increase in loaf height, specific volume, porosity, and moisture content. Loaves had higher moisture content, the development of mold during storage was suppressed for a longer period, and breads were more palatable than either conventional or chemically acidified ones [53]. The authors suggest that _L. brevis_ and _L. paralimentarius_ are the two most promising species for the production of high-quality, gluten-free doughs and breads made using millet flour [53].  
The results reported in [PERSON] et al. (2019) [53] are supported by [PERSON] et al. (2014) [54]. The latter study investigated the effects of sourdough fermentation on doughs and breads obtained with maize flour. The rheological analysis found that it shortened relaxation time, and resulted in the lowest elastic modulus, indicating a softer and less elastic dough. Fermentation also increased loaf volume by 25-26%, and improved texture and larger cells were observed. However, [PERSON] et al. (2011) [55] tested the effect of sourdough fermentation on dough and bread produced with buckwheat flour, with conflicting results.  
Although sourdough fermentation seems to be an interesting improvement strategy, both from a nutritional and technological point of view, like [PERSON] et al. (2008) [14], we believe that further studies are necessary. In particular, close attention should be paid to a very interesting secondary advantage related to sourdough fermentation--the ability of some lactic acid bacteria to produce techno-functionalized exopolysaccharide. This topic was extensively examined in [PERSON] et al. (2018) [56]. The authors noted that, typically, exopolysaccharides produced by lactic acid bacteria are high molecular weight polymers with physiochemical properties that are similar to commercial hydrocolloids or gums, and could be considered as a potential (natural) improver for gluten-free formulations. Although these molecules are able to mimic gluten network behavior, the authors observe that several factors can influence their impact. Flour composition, acidification potential, the type of exopolysaccharide, and many other factors must be carefully considered. However, since their in-situ production has no labeling requirements, increases shelf life, and improves nutritional content, further investigations are urgently needed.