# Functional and Healthy Features of Conventional and Non-Conventional Soundoughs
## 2 Sourdough Technology  
Based on the technology applied for their production, three main types of sourdough can be distinguished: type I, which is the artisan bakery firm sourdough; type II, referring to industrial liquid sourdoughs; and type III, which indicates industrial dried sourdoughs [15; 16] (Figure 1). Usually, mature type I sourdough contains a mixture of typical yeast and mesophilic LAB strains that characterize sourdough-based products [6]. The stability of the dough depends on the type of flour, the quality and nutritional value of the cereals, the temperature and humidity during processes, and the microbial composition of the inoculum [17; 18]. The common yeast species are mainly _Saccharomyces cerevisiae_, _Kazachstania humilis_ (formerly _Candida humilis_), _Kazachstania exigua_, _Pichia kudriavzevii_, and _Torulspora delbrueckii_[19; 20]. Moreover, almost 95% of the traditional sourdough population is dominated by heterofermentative LAB alone or in association with homofermentative lactobacilli [15; 21]. _Lactobacillus santrancisensis_ (currently _Fructilactobacillus santrancisensis_) was most frequently detected in association with yeasts belonging to _Kazachstania_ species, predominantly _K. humilis_[22; 23; 24]. Other frequently representative LAB include _Lactobacillus plantarum_ (currently _Lactipaltobacillus plantarum_), _Lactobacillus brevis_ (currently _Levilactobacillus brevis_), _Leuconostoc_ spp., and _Weissella_ spp. [1; 25; 26]. To avoid any confusion for the _Lactobacillus_ strains reported in previous studies with the former classification of the genus, the old name of the species will be maintained in the present review; the following link is suggested for the appropriate name conversion:  
[[http://lactobacillus.ualberta.ca](http://lactobacillus.ualberta.ca)]([http://lactobacillus.ualberta.ca](http://lactobacillus.ualberta.ca)), accessed on 17 March 2021. The type I sourdough is prepared according to the traditional method, conducted by daily refreshments, also called \"back-slopping\", which keeps it metabolically active. Accordingly, a selection of sourdough microbiota occurs, due to the back-slopping, which is repeated five to ten times [8; 27]. These sourdoughs are typical of various traditional Italian sweet baked products, including those that are commercialized and consumed during holiday seasons, such as _Panettone_ and _Colomba_[3; 18; 28]. Type II and III sourdoughs (the latter is made by dehydrating the stabilized form of type II sourdough) were developed for industries with the aim of providing a more standardized process [6]. Both are made with selected cultures added at a ratio of 100:1 (LAB to yeasts) to obtain specific features of the baked products and inhibit the growth of unwanted microbiota [8]. The selection of microbial strains useful as starter cultures is fundamental for sourdough industries and relies on various metabolic traits that have both technological and functional interest [29; 30]. In this context, qualified microbial culture collections, constitute a fundamental cornerstone for the investigation of sourdoughs' microbiota to select strains with desired features [31]. Among LAB, the selection of potential starters is generally made within the _Lactobacillaceae_ and the most often used are acid-tolerant strains such as _L. amylovorus_, _L. panis_, _L. pontis_, and _L. reuteri_[27; 32; 33]. Different non-lactobacillus strains have also been tested as suitable starters because of the positive effect of their compounds on the sourdough flavor, which can open new prospects in the sourdough industries. As reported by [PERSON] et al. [34], _Pedicoccus pentosacaus_ OA1 and S3N3 and _Leuconostoc citream_ PRO17 were selected on the basis of optimal acidification and growth performance, as well as the intense proteolytic activity in whole wheat flour doughs. Recently, AAB have also been considered useful starters for the production of desired metabolites [7].