## 3 Results and Discussion
### Arthospira Plateensis Fermentation
rhamn_s GG is a probiotic commonly supplemented to fermented milk [38], but applications to other matrices have also been evaluated. For instance, a sausage supplemented with _L. rhamn_s GG has been produced [39] though this strain grew to a lesser extent than in _A. platensis_. During fermentation, the initial pH of the hydrated _A. platensis_ biomass decreased from 7.0 \(\pm\) 0.1 to 5.2 \(\pm\) 0.1 in the first 24 h for both samples and remained stable until the end of the fermentation process. This decrease in pH during fermentation reflects the growth of the LAB strains with consequent production of organic acids, mainly lactic acid. Considering the possibility to use lactic acid-fermented _A. platensis_ in a food supplement formulation or as an ingredient, the survival of LAB was evaluated after a lyophilization process. _L. rhamn_s GG was reduced at 8.22 \(\pm\) 0.02 log CFU/g (_p_ < 0.05), and _L. casei_ 2240 was reduced by more than 1 log CFU/g (from 8.44 \(\pm\) 0.28 to 6.9 \(\pm\) 0.03 log CFU/g) (_p_ < 0.05) (Figure 1A). The second fermentation process was carried out on _A. platensis_ samples treated at 121 \({}^{\circ}\)C for 20 min in order to eliminate the presence of any microbial contamination. The absence of residual contamination after treatment was confirmed by plate count below the detection limit (1 log CFU/g). The sterilization treatment involves the use of a particular apparatus, the autoclave, and high energy to reach the temperatures and pressures required by the process. This treatment is therefore longer and more expensive than that based on UV rays, but the results show that it is certainly more effective in reducing the initial microbial concentration of the product. Following the heat treatment, the characteristic green-blue color of _A. platensis_ changed to a dark green, brownish color. This may be due to the degradation of pigments such as carotenoids, xanthophylls, phycocyanins and chlorophyll caused by the high temperatures reached [40; 41; 42]. The growth trend of LAB strains is presented in (Figure 1B). In particular, after 24 h, _L. casei_ 2240 increased by 2.13 log CFU/g (from 7.57 \(\pm\) 0.142 to 9.70 \(\pm\) 0.320 log CFU/g) (_p_ < 0.05) and _L. rhamn_s GG by 1.5 log (from 7.10 \(\pm\) 0.06 to 8.63 \(\pm\) 0.21 log CFU/g) (_p_ < 0.05) and then remained constant (with no significant differences) up to 48 h.  
The ability of these _Lacticaseibacillus_ species to grow on different matrixes has been challenged over the years, with different results [25; 39; 43; 44]. In particular _L. casei_ and _L. rhamn_s strains grown on sterilized vegetables' by-products increased by more than that observed on _A. platensis_[45]. However, the ability of this cyanobacterium to boost the growth of LAB is known in the literature [20], and because of its richness in small peptides and proteins, _A. platensis_ can be considered a good matrix to allow for the growth of LAB species such as _L. casei_ and _L. rhamns_. After fermentation of the sterilized biomass, a lower acidification rate than that of the UV-treated fermented samples was observed. The pH value of the sterilized fermented biomasses after 24 h was 5.8 \(\pm\) 0.1 and 6.1 \(\pm\) 0.1, respectively, for _L. casei_ 2240 and _L. rhamn_s GG and also remained stable at 48 h of fermentation (Figure 1B). Analogously to the UV-treated samples, a lyophilization process was applied to the sterilized products after fermentation. A decrease in the microbial concentration of 0.5 log CFU/g was observed for both strains; in particular, _L. rhamn_s GG was reduced to 8.15 \(\pm\) 0.05 log CFU/g and _L. casei_ 2240 to 8.86 \(\pm\) 0.05 log CFU/g (_p_ < 0.05) (Figure 1B). _L. rhamn_s GG better survived the lyophilization process than _L. casei_ 2240, whose viability showed a decrease of more than 1 log CFU/g. The survivability of freeze-dried strains is of particular importance for the production of foods containing live cells, and, for this reason, many studies focus on enhancing the viability of LAB after this process [46; 47].