## 3 Results and Discussion
### Arthospira Plateensis Fermentation
The LAB species considered in the present work, _L. casei_ and _L. rhamnus_, provided significantly different results in the production of heptadecane in the differently treated substrates, which is indeed linkable to LAB fermentation [68]. It can be speculated that the production and/or release of this compound may depend on the applied LAB species. The same phenomenon can be observed also for pentadecane. A higher amount was detected in the UV-treated samples when compared to the sterilized ones. It can be observed that the quantity of hydrocarbon grew following fermentation when both the strains were used (Supplementary Table S1). The significant difference observed in the fermented biomasses (i.e., heptadecane: UV 2240 = 7.65 \(\pm\) 1.95 \(\upmu\)g/g; ST 2240 = 2.53 \(\pm\) 0.66 \(\upmu\)g/g) can be ascribed to the different stabilization processes applied; the higher concentration of these volatiles in the UV-treated biomass could be ascribed to the metabolism of the endogenous microflora typical of the spirulina biomass. Since the UV treatment, unlike the heat treatment, did not completely eliminate contaminating microflora, this behavior can be ascribed to the residual microflora deriving from cultivation in open ponds. Terpenes, the second most important class in terms of concentration, were positively influenced by sterilization treatment, and an interaction between the two factors was observed (\(p=0.013\)). Terpenes and norisoprenoids are fundamental compounds in food aroma. \(\upbeta\)-cyclocitral and \(\upbeta\)-ionone, with pleasant fruity and floral notes, are two volatiles typical of cyanobacteria. The formation of these compounds is due to the oxidation of carotenoids following caroten oxygenase. Norcarotenoids are an important group of compounds formed by several species of cyanobacteria, generated by enzymatic degradation of carotenes and carotenoids. For example, the oxygenase reaction of carotenoids was first described in Microystis. \(\upbeta\)-cyclocitral is formed by the cleavage reaction of \(\upbeta\)-carotene catalyzed by the enzyme [59]. \(\upbeta\)-ionone and norcarotenoids of the \(\upbeta\)-ionone-type are an important group of compounds that were found in axenic cyanobacterial cultures and a monoxenic culture of _Phormidium_ sp. [69]. Significant differences in the presence of \(\upbeta\)-cyclocitral, the compound that mainly characterizes the class of terpen and norisoprenoids, were found because of the biomass stabilization treatment (\(p<0.001\)), while no significant differences were found in \(\upbeta\)-ionone production. Regarding the production of aldehydes and ketones and/or release, both fermentations and treatments produced significant differences in the samples (\(p<0.02\)); in addition, a strong interaction was noticed between the two factors for these two volatile classes (\(p<0.005\)). While differenced were noted among the two stabilization treatments (\(p=0.012\)), ketone concentration was mainly affected by fermentation, (Figure 3, Supplementary Table S1). In particular for aldehydes, a reduction following the fermentation of the sterilized biomass using both the tested strains was observed. Conversely, by fermentation of the UV-treated biomass, the amount of aldehydes increased. This behavior could be due to the presence of the epiphytic bacteria typical of the spirulina biomass. Considering these data, it can be suggested that fermentative LAB can reduce the amount of these compounds, but the typical microflora of _A. platensis_ can produce aldehydes, thereby giving the fermentedbiomass a different aroma profile. Hexanal was found in several microalgae [70; 71; 72; 73]. Fermentation of sterilized biomass by both of the strains led to a significant diminution of hexanal content (\(p<0.01\)), while only fermentation of the _L. rhamn_s GG strain seemed to produce this compound in UV-treated samples.