## 3 Results and Discussion
### Arthospira Plateensis Fermentation
Although isoamyl alcohol has also been reported in phototrophic cultures of _Chlorella vulgaris_[71], in this study, it was not found in treated biomass, but rather in unfermented _A. platensis_ biomass. The UV treatment and the sterilization process produced significant differences in the total amount of furans, pyrazines and sulfur compounds. Four furans were found as a component of the aromatic profile of fermented _A. platensis_ biomass. 2-Pentylfuran is an important product of lipid degradation and is responsible for beamy and licorice-like sensory qualities in various food products [79]; it has been associated with the typical beany, green and metallic odor of spirulina, and it was detected in considerable percentages of about 10% in fermented spirulina samples in a previous study [30]. In our case, this furan was formed following the sterilization of the biomass (0.10 \(\pm\) 0.04 ug/g), but it decreased following fermentation, while in UV-treated samples, it was not detected in the not fermented substrate, but it increased after fermentation. Pyrazines are molecules typical of roasted and thermally treated foods. Seven pyrazines were found in the analyzed samples, and most of them were connectable to the sterilization process. For example, 2,5-dimethylpyrazine, a pyrazine with a typical chocolate aroma, was found in the sterilized biomass and not in the UV-treated samples. Interestingly, some of these compounds were also produced following lactic acid fermentation. Small amounts of 2-methylpyrazine were produced by _L. rhamns_ GG (0.02 \(\pm\) 0.00 ug/g) in the sterilized biomass. This is not the first time that the production of pyrazine by _L. casei_ group bacteria was underlined [80]. Among all of the pyrazines detected in the tested samples, 2,5-dimethylpyrazine and 2-methylpyrazine are of particular interest, because these compounds have been associated with the off-flavor of _A. platensis_[30]. Similar behavior was observed for sulfur compounds, prevalently found in the sterilized samples. Dimethyl disulfide is a sulfuric compound formed following thermal oxidation of other volatile sulfur compounds such as methanethiol [72]. The number of sulfur compounds seemed to be related especially to the stabilization treatment, as the concentration of these compounds was higher in the sterilized samples when compared to those treated with UV (\(p\) = 0.019). Generally, sulfur compounds may contribute to the unpleasant odor of algae products because of their low threshold value. [PERSON] et al. (2017) stated that sulfides were responsible for about 26% of the total odor profile of sea tangle extract, and fungal fermentation lead to a total reduction of dimethyl disulfide after two days from the inoculation [33]. In our case, the fermentation step did not reduce the amount of this compound detected only in UV-treated materials (Supplementary Table S1). Esters, with floral and waxy notes, are the category that presented the lower quantities in the analyzed samples. Four compounds were identified, and this is in line with what has been reported in other studies [30; 33]. The stabilization treatment did not seem to affect their content, while fermentation led to a decrease in the initial quantity (\(p\) = 0.021) (Supplementary Table S1).