# Probiotics in the Sourdough Bread Fermentation: Current Status
## 5 Enzymes in Sourdough
### Hydrolases
#### 5.4.1 Amylase, Inulinase, and Their Impact on Bread Structure and Properties  
Several types of amylases act on starch, mainly liberating glucose for the fermentation and improvement of the bread's color, flavor, and shelf-life [210]. The main groups are endoamylases, exoamylases, and debranching amylases. Among the endoamylases, \(\alpha\) \begin{table}
\begin{tabular}{c c c} \hline \hline
**Enzyme** & **Microorganisms** & **Reference** \\ \hline Xylanase & _Sporotrichum thermophile_ BJAMDU5 & [184] \\  & _Pichia pastoris_ & [185] \\  & _Bacillus subtilis_ & [186] \\  & _Myceliphthora thermophila_ BJTLRMDU3 & [187] \\ Phytase & _Lactobacillus casci_ & [188] \\  & _Enterobacter_ SP. ACSS & [189] \\  & _Sporotrichum thermophile_ & [190] \\  & _Aspergillus niger_ NCIM 563 & [191] \\ Amylase & _Rhizopus oryzae_ & [192] \\  & _Bacillus subtilis_ US86 & [193] \\  & _Bacillus subtilis_ M13 & [194] \\  & _Streptomyces baldium_ DB-1 & [195] \\ Glucose Oxidase & _Aspergillus niger_ & [196] \\  & _Penicillium notatum_ & [197] \\  & _Aspergillus niger_ & [198] \\  & _Aspergillus niger_ & [199] \\ Peptidase & _Rhizopus oryzae_ & [192] \\  & _Bacillus subtilis_ PF1 & [200] \\  & _Bacillus subtilis_ & [201] \\  & _Bacillus puntilus_ SG2 & [202] \\ Lipase & _Aspergillus niger_ MTCC 872 & [203] \\  & _Pseudomonas fluorescens_ (NRLL B-2641) & [204] \\  & _Bacillus subtilis_ I-4 & [205] \\  & _Bacillus_ sp. MPTK 912 & [206] \\ Cellulase & _Sporotrichum thermophile_ BJAMDU5 & [203] \\  & _Streptomyces strain_ C188 & [207] \\  & _Cellulomonas uda_ & [208] \\  & _Trichoderma reseei_ NCIM 1186 & [209] \\ \hline \hline \end{tabular}
\end{table} 
Table 4: List of microorganisms that produce the main enzymes used in the bakery. amylase (EC 3.2.1.1) is the main one, acting on \(\alpha\)-1,4 bonds in the amylose and amylopectin chains. The group of exoamylases includes glucoamylase (EC 3.2.1.3), \(\alpha\)-glucosidase (EC 3.2.1.20), and \(\beta\)-amylase (EC 3.2.1.2) promoting the hydrolysis of terminal glycosidic units. Debranching amylases act on \(\alpha\)-1,6 branch bonds, and pullulanase (EC 3.2.1.41) is the leading representative [211]. Starch/amide is present in around 70-75% of wheat flour. It comprises a linear chain of \(\alpha\)-1,4 glycosopyranoside (amylose) and a linear chain of \(\alpha\)-1,4 glycosopyranoside with \(\alpha\)-1,6 branch points (amylopectin). During the baking process, the bread undergoes several changes in starch retrogradation relative to the crystalline structure of amylose and amylopectin. These changes occur not only in baking but also during the cooling and storage processes [212]. Starch retrogradation is a process in which disaggregated amylose and amylopectin chains in a gelatinized starch paste reassociate to form a more ordered structure [213]. It is a pivotal issue in bread aging and is the cause of bread hardening. The amylases produced by LAB strains reduce the aging process during bread storage [214]. Amylase-producing microorganisms in the sourdough environment are essential in converting starch into fermentable carbohydrates such as maltodext, maltose, sucrose, and glucose. LAB are sources of maltose phosphorylase, which generate D-glucose, \(\beta\)-D-glucose, 1-phosphate, and 1,6-\(\alpha\)-glucosidase, which hydrolyzes \(\alpha\)-(1-6)-glucooligosaccharides [3]. In addition, wheat has \(\alpha\)-amylase, \(\beta\)-amylase, and glucoamylase activity, but at pH \(<\) 4.5, only glucoamylase maintains its activity. Microorganisms in the sourdough microbiota produce inulinase (\(\beta\)-2, 1-D-fructan-fructan-hydrolase--EC 3.2.1.7)--a glycosylase that hydrolyzes the \(\beta\)-2.1 bonds of fructose of the fructose polymer, inulin. Inulinase can reduce the number of oligosaccharides, disaccharides, monosaccharides, and fermentable polyols (FODMAPs) in bread [78]. FODMAPs are associated with irritable bowel syndrome.