# Probiotics in the Sourdough Bread Fermentation: Current Status
## 4 Probiotics and Postbiotics in Sourdough and the Impact on Human Health  
Probiotics are live microorganisms that confer a health benefit when administered in adequate amounts. In addition, new terms have been used to name microbial metabolites from non-viable cells, including paraprobiotics, parapsychobiotics, ghost probiotics, matabiotics, tyrdallized probiotics, bacterial lysates, and postbiotics. However, the last term is being mightily used for the vital concept of promoting health. Postbiotics means non-living microorganisms and is a preparation with inanimate microbial cells or their components that promote host health. Metabolites and cellular structures from microorganisms from sourdough are potential postbiotics [47; 48]. Sourdough microbiota are involved in a complex interaction that engenders beneficial compounds for human consumption. With the current molecular methods, a better characterization of sourdough microbiota has been described [49; 50]. Moreover, whole-genome sequencing has permitted more accuracy in confirming the requirements for characterizing probiotic microorganisms [25]. The probiotics and postbiotics of sourdough provide health benefits in addition to the essential nutritional components of the bread itself. A fermented food passes through a process with microorganisms and enzymes converting macronutrients into bioactiveproducts. LAB is one major microorganism group with several probiotic strains applicable to cereal fermentation. LAB are classified as Gram-positive bacteria which include low guanine + cytosine (G + C) content as well as being acid-tolerant, non-motile, non-spore-forming, and are rod- or cocci-shaped. The main function of LAB is to produce lactic acid, that is, the acidification [40]. The most common genera found in sourdough were _Lactobacillus_, _Leuconostoc_, _Weissella_, and _Pediococcus_. However, the genera _Streptococcus_, _Enterococcus_, and _Lactococcus_ are found, although less frequently [51; 52]. The second group of microorganisms are the yeast, and more than 20 species dominated by the genera _Saccharomyces_ and _Candida_ are found. LABs and yeasts are naturally found in the microbiota of the cereal flour used or can be added as a starter. Some native microorganisms found in sourdough are listed in Table 1.  
No strong relation between the microbiota and regional origin has been proven until now [34; 53]. However, in Brazil, _Lactobacillus fractiminis_ was the prevalent species rather than _Lactobacillus__santranciscensis_. Other bacteria could be present. At a temperature of 30 \(\pm\) 1 \({}^{\circ}\)C, unusual bacterial groups such as _Pseudomonas_ and _Enterobacteriaceae_ can proliferate. At a temperature of 21 \(\pm\) 1 \({}^{\circ}\)C, there may be a prevalence of LAB, which are safer for human consumption [54]. Other factors that have been identified that could influence the microbiota. Insects could be a reservoir of _Lactobacillus__santranciscensis_[55], commonly found in type I sourdough. _Lactobacillus__delbrueckii_ and _Lactobacillus__reuteri_ groups from vertebrate-host interactions are typical occurrences in type II sourdough [33]. In Italy, bakery LAB species such as _Weissela_ spp. and _Streptococcus_ spp. are in the local environment [50]. In addition, the water used in sourdough type I could influence its microbiota [56]. It has been demonstrated that _Lactobacillus_, _Streptococcus_, _Enterococcus_, and Lactococcus are endophytic components of wheat and, as such, a source of sourdough microbiota [52]. The sourdough microbiota changes with decreasing pH, whereas at the beginning, there is abundant Proteobacteria phylum in mature sourdoughs, which at the end is replaced by Firmicutes [54; 57]. [PERSON] et al. [58] demonstrated that the extraction rate of wheat flour from cultivars _Triticum aestivum_ and _Triticum durum_ modified the microbiota community in sourdough type I. The study showed that during fermentations, both controlled and uncontrolled pH conditions up to 4.0 yield similar LAB and yeast species [59].