## 4 Discussion
This strain observed a decrease in the percentage of PUFAs in respect to SFAs when glucose was used as a carbon source as opposed to glycerol [15]. Therefore, the raw glycerol used in this case could produce the same output of DHA as that obtained using glucose as a main carbon source from the commercial Sabouraud medium but using a substrate waste from another productive activity. This result is similar to that obtained in other marine fungoides such as _Thraustochytrium_ sp. [31] and _Aurantiocytrium_ sp. [32], where the total production of polyunsaturated fatty acids omega-3 do not demonstrate significant differences between glucose and raw glycerol. A different way to compare the results from the carbon source used could be from a nutritional point of view. Accordingly, the relationship of unsaturated fatty acids in respect to saturated ones can be calculated for strain NCYC4007. In the study, the relationship indicates that the acquired biomass obtained when raw glycerol was used presents a lower degree of unsaturation (0.5), followed by analytical grade glycerol (0.9) and, finally, glucose (1.0). This indicator of unsaturation has been associated to the oxidative stability of fatty acids [33] and, in this case, suggests that lipid contents acquired from the biomass obtained when glucose was used have a greater possibility to oxidize than lipids produced when raw glycerol was used. Thus, the acquired biomass with raw glycerol, despite having a lower unsaturation level (0.5), could present a greater stability of the PUFAs against oxidation in a bioprocess on a larger productive purposes scale than that of the biomass acquired with glucose as a carbon source (1.0). In greater detail, the acquired profiles obtained when glucose and analytical grade glycerol were used as a carbon source highlight the presence of oleic acid (C18:1; Table 2), a precursor in the synthesis of polyunsaturated fatty acids belonging to the omega-3 family, such as DHA and omega-6 [34]. Meanwhile, with raw glycerol, a high production of linoleic acid was observed (C18:2, Table 2), a precursor in the synthesis of fatty acids belonging to the omega-6 family, which can be transformed via catalysis \(\Delta\)15 desaturase to \(\alpha\)-linoleic acid (C18:3) and, also, is a precursor to DHA synthesis [34]. These results suggest that the NCYC4007 strain could have more than one metabolic pathway for DHA synthesis, which could be induced depending on which substrate is used, according to what was observed in _Schizochytrium_[28], _Aurantiochytrium_ and _Thraustochytrium_[35]. The TC production observed in strain NCYC1146 (19% in ODW) is greater than described for _R. mucilaginousa_[13] and _R. glutinis_[14], corresponding to an 8% or 10% TC of ODW, respectively. The maximum production of TC in less time was observed when raw glycerol is used, similar to what was observed for the production of DHA in NCYC4007. This observation could be related with a greater activity of the biosynthesis routes due to the use of raw glycerol as a substrate as opposed to glucose. This has been described as a species of _Thraustochytrids_, where the polyktetide synthase pathway (PKS) and that of mevalonate were involved in DHA production, used for the production of carotenoids and found to be more active in a glycerol medium to one with glucose [36]. The carotenoid pigments profile of strain NCYC1146 is similar to the profiles from _Thraustochytrids strains_ AMCQS5-3, AMCQS5-5 [12] and ONC-T18 [36] that produce the greatest concentration of \(\beta\)-carotene, followed by echinenone (intermediary of 3-hydroxyechinenone) and canthaxanthin. It was observed that extending the culture time of the _Thraustochytrids_ ONC-T18 strain [37] could synthesize other xanthines such as astaxanthin due to 3-hydroxyechinenone, and the adonirrubin are precursors of this substance [37], both present in the carotenoids profile of NCYC1146 (Figure 3).