## 2 Materials and Methods
### Experimental and Statistical Analysis  
The bacterial strain adopted for the experimental investigation is the _Lactobacillus paracasei_ CBA L74 (named LpCBAL74 in the following for brevity), supplied by Heinz Italia SpA with International Depository Accession Number LMG P-24778. It is a Gram-positive, facultative heterofermentative, oxygen-tolerant anaerobic bacterium, previously stored in freeze-dried form at \(-20\)\({}^{\circ}\)C and subsequently revitalized (for 24 h at 37 \({}^{\circ}\)C) in a culture medium consisting of animal-free broth [23]. The chosen substrate for the fermentation process was a rice flour-based suspension made of rice flour (15% as weight/volume ratio, supplied by Heinz Italia SpA), water (83 wt/vol%), and glucose (2 wt/vol%). The rice flour was thermally treated for 90 min at 121 \({}^{\circ}\)C and water was autoclaved (121 \({}^{\circ}\)C for 20 min) to decrease possible microbial loads and the suspension obtained sterilized through turdallisation process to eliminate vegetative forms of bacteria by carrying out two thermal cycles constituted by a heating step at 70 \({}^{\circ}\)C for 30 min and a cooling step at 37 \({}^{\circ}\)C for 30 min ([PERSON] et al., 2020). The starting inoculum volume (characterized by a concentration of 10\({}^{8}\) CFU/mL) for each test was 9 mL to guarantee the starting biomass concentration of 10\({}^{5}\)-10\({}^{6}\) CFU/mL (CFU is the standard Colony Forming Unit). The fermentation process was carried out in a Pyrex(r) lab-scale bioreactor with a maximum volume capacity of 1.5 L and working volume of 1 L. As shown in Figure 2, the bioreactor has a cylindrical shape, i.e., 20 cm in height and 10 cm in diameter, and is coated with an external jacket, 18 cm in height and 14 cm in diameter. Moreover, the bioreactor is equipped with: (i) a mixing system constituted by two stainless steel stirrers, of which one has inclined blades and the other vertical blades (i.e., of Rushton type), both connected to a three-phase asynchronous electric motor (0.25 Hp, 0.18 kW, 1310 rpm); the proposed system allows the regulation of the stirring speed by means of a speed reducer limiting it at 180 rpm, which was preliminarily evaluated as the optimal value to obtain a uniform mixing of the suspension [22]; (ii) a thermal conditioning system consisting of a [PERSON] thermo-controlled bath that permit both to guarantee a turdallisation process and to maintain the temperature at 37 \({}^{\circ}\)C during the bacterial growth; (iii) a [PERSON] Toledo pH control system composed of probe and peristaltic pump. The experimental investigation concerned the evaluation of the biomass concentration and the lactic acid production without or with pH control at a value of 5.8, ensured by pumping in a solution of NaOH 0.2 M. Such a value is recognized to be, within the range 5 to 6, the optimal one to produce lactic acid by using Lactobacillus strains [24; 25]. The  
Figure 2: Experimental set-up of the fermentation system. fermutation process lasted 24 h at 37 \({}^{\circ}\)C. Before using, each component of the system underwent a sterilization cycle in autoclave for 20 min at 121 \({}^{\circ}\)C.  
To evaluate the bacterial growth, the fermenting suspension was sampled every 2 h [5,10]. Each sample (10 mL of volume) was aseptically drawn and used for the microbiological and chemical analysis. To this end, the samples, after collection and dilution, were seeded on a Petri dish with MRS agar supplied by Oxoid and incubated for 48 h at 37 \({}^{\circ}\)C under anaerobic conditions. The bacterial count was made through the spread plate method. The lactic acid quantity produced during the fermentation process was evaluated by using the High-Performance Liquid Chromatography apparatus (Agilent Technologies, Santa Clara, CA, USA), equipped with an Agilent Zorbax C18 column with UV light detector. For the measurements, a solution of NH\({}_{4}\)H\({}_{2}\)PO\({}_{4}\) 0.1 M with a flow rate of 0.8 mL/min was used as eluent.