# Probiotics in the Sourdough Bread Fermentation: Current Status
## 2 Sourdough Fermentation Types: Inoculum and Technology Processes  
Sourdough fermentation can be classified according to the inoculum (type I, II, and III) and the technology process (type 0, I, II, and III). According to inoculum, type I uses the microorganisms present in the dough, which results in spontaneous fermentation and utilizes back-slopping to propagate the sourdough microbiota. This process is common in artisan bakeries and homes. Control parameters include temperature, number, and time of back-slopping in artisan bakeries. Type II inoculum are frequently utilized in industrial processes, where a starter culture is added to sourdough fermentation according to the objectives and results desirable in the final process. Type III is a hybrid and combines type II by using a starter culture with type I for propagating the sourdough with back-slopping. Type III is common in artisan bakeries and industrial ones [27]. According to the production and process, sourdough fermentation can also be classified into four major types. The simple type 0 fermentation starts with a flour-water mixture and is allowed for a limited time. LAB species that are naturally present in the flour, grow faster are more prolific than yeast. [PERSON] et al. 2013 [28] compared the growth of two _Lactobacillus paracasei_ strains with two _Saccharomyces cerevisiae_ strains. LAB had the highest counts over time and microbial growth after 10 h of fermentation. The highest value for LAB strains was 8.91 log CFU/g, and then 8.66 log CFU/g. One _S. cerevisiae_ strain reached 8.03 log CFU/g, and the other, 0.21 log CFU/g. At 6 h of fermentation, LABs were 8.66 log CFU/g and 8.33 log CFU/g. Yeasts showed 7.18 log CFU/g and 7.08 log CFU/g. The growth kinetics of six strains of LAB: _Fruticlactobacillus santranicscensis_, were compared with five strains of yeast: _Kazachstania humilis_, from sourdough, by [PERSON] et al. 2021 [29]. Three predictive models were used to evaluate the behavior of co-cultivated microorganisms: The zwittering model based on [PERSON]'s equation, [PERSON] and [PERSON] function, and Schiraldi's function. The results showed that _F. santranicscensis_ strains significantly steer the growth kinetics affecting the ratio of bacterial to yeast cells, where the yeast strains of _K. humilis_ adapt to the bacterial strains. The authors discuss the possibility of metabolic interactions for stabilizing the sourdough consortium through communication, such as quorum sensing, to control population density, among other functionalities. In another co-culture article with LAB and yeast, the yeast population size decreased in the presence of LAB regardless of the strain, while the LAB's population size was rarely influenced by the presence of yeast [30]. In type 0 fermentation, bioactive molecules and organic acids (lactic and acetic acids) are produced lowering the pH (pH-4), but it is controversial if this type of fermentation is a true sourdough. The time limit is insufficient to produce other characteristic products of sourdoughs and is more known as sponge dough [27]. Type I is a traditional method for preparing sourdough and consists of spontaneous fermentation in a flour-water mixture at an ambient temperature of less than 30 \({}^{\circ}\)C for 24 h or less and back-slopping frequently. This fermentation increases the quality of the final baked good [27; 31]. Type II is when a starter culture initiates the fermentation process and is used to develop desirable characteristics for the baking industry. It is a sourdough in liquid form with controlled parameters [31; 32]. Type III can be dried or lyophilized. It is preferable for use in an industrial bakery because it has a higher stability quality than fresh sourdough [31; 33]. The fermentation temperature used is above 30 \({}^{\circ}\)C and in a single time stage between 24-72 h [34]. The fermentation process will change depending on the added materials, such as the addition of naturally rich products in microorganisms: fruits, yogurt, or another material [35].