## 4 Discussion
### Chemical Characterization
2,4-decadienal is known for its greasy aroma, accompanied by green, fresh, and citrus notes. When present in high quantities, its flavor resembles that of fried chicken, with an underlying rancid aftertaste [115]. Given the low detection threshold (approximately 0.0003-0.00013 mg/kg) and high initial concentration of the 2,4-decadienal isomers, it can be inferred that these compounds significantly contributed to the characterization of the UL odor. In _Ulva conglobata_, it was demonstrated that 2,4-decadienals were produced via hydroxy eicosatetraenoic acids (HETEs), derived from arachidonic acid, by means of a crude enzyme that was isolated from the seaweed [118]. It is recognized that microbial activity can diminish the presence of these compounds, associated with a \"fishy aroma\" in fermented seaweeds [112; 119]. Similarly, exposure to light also appears to contribute to their decline [120]. The significant decrease in 2,4-decadienals in CTRL seemed to be primarily influenced by the presence of microorganisms, rather than the level of light exposure, which was similar across all the samples. 1-Hexanol carries a distinctive green and herbaceous aroma, with a slight alcoholic hint, reminiscent of the scent of freshly cut grass [115]. Despite its medium odor threshold (1.21 mg/kg), it was reported that odor contribution in the seaweed _Ulva australis_ was low [59; 116]. 1-Hexanol can be generated through the peroxidation of unsaturated fatty acids. Additionally, aldehydes can be converted to their corresponding alcohols through a reaction catalyzed by aldehyde dehydrogenases (ALDHs) [121]. In the case of fermented seaweeds, it has been observed that 1-hexanol undergoes a transformation into 1-hexanol through the action of enzymes released by microorganisms [122]. In UL-CTRL, 1-hexanol reached its maximum at day 12, surpassing other abundant compounds such as 2,4-decadienals and 8-heptadecene (isomer 1), while in UL treated with MAP and VAC, its presence remained relatively low. Therefore, its occurrence appeared to be related to the aerobic activity of the microbiome found within the seaweed. Benzaldehyde exhibits a sweet and fruity aroma, with a very characteristic flavor that resembles bitter almonds and cherries [115]. Although this compound possesses a moderate odor threshold (0.55 mg/kg) and seems to contribute to the aroma of certain species of _Ulva_ spp., its influence is less noticeable compared to other aldehydes present [59; 116]. In our study, benzaldehyde seemed to have an impact on the aroma profile of UL processed, particularly with MAP, although this influence appeared to be beneficial, considering the organoleptic attributes associated with the compound. There are many hypotheses about the metabolic pathway for the production of benzaldehyde in marine macroalgae, such as: thermally generated and derived from Strecker degradation of amino acids [123]; from aromatic compounds through enzymatic peroxidation by haloperoxidases, in the absence of halides [124]; and from amino acid derivatives by chemical routes as a consequence of lipid oxidation (this can occur either directly through free radicals derived from lipid hydroperoxides, or indirectly through reactive carbonyls derived from lipids) [125]. Similar to our results, [PERSON] et al. [56] identified benzaldehyde as the most abundant aromatic compound in _U. lactuca_. Its concentration seemed to be influenced by the storage time for all treatments, with an emphasis on samples preserved by MAP. No existing literature was found regarding the characteristic aroma of 8-heptadecene, and its presence did not seem to impact the aroma of seaweeds from the genus _Ulva_ spp. Some studies indicated 8-heptadecene as the primary hydrocarbon in marine green macroalgae [106; 112; 126]. The compound was isolated from the seaweed _Bryopsis maxima_ (Chlorophyta), being identified as the (Z)-8-heptadecene stereoisomer [127]. Limited research exists regarding the changes in VOCs in seaweeds as influenced by storage duration. [PERSON] et al.