## 4 Discussion
### Chemical Characterization  
GC-TOF-MS Analysis  
Seaweeds are known for their unique sensory properties, and certain terms are commonly used to describe their distinct flavors and aromas. Some descriptions frequently associated with \"laver\" (_Porphylra_ spp., _Pyropia_ spp., and _Neopyropia_ spp. ; Rhodophyta) are a distinct sea taste, evoking the essence of the ocean when fresh; the dried form exhibits flavors similar to mushrooms and dehydrated fruits such as raisins; and, when toasted or cooked, it takes on a more fishy profile, suggestive of roasted sardines. For \"sea-lettuce\" (_Ulva_ spp. ), the most commonly used organoleptic descriptors are: when fresh, slightly bitter with green and fatty aromas and some notes of green vegetables such as cucumber and herbs (due to the presence of various aldehydes); when dried, the aroma resembles the marine environment, due to the production of dimethyl sulfide (DMS), with notes of cut grass or _matcha_ (green tea) (26; 104; 105). [PERSON] et al. (2016) identified in _P. umbilicalis_ the highest levels of total volatile alcohols and ketones in contrast to the other six species of dehydrated seaweed they stud ied, including _U. lactuca_, while no halogenated compounds were detected. Consistently, the aroma of \"laver\" seaweed appears to be primarily influenced by the presence of alcohols and ketones, with a lesser contribution from aldehydes and sulfur compounds (see Supplementary Material, Figure S2). Despite being abundant, hydrocarbons do not seem to significantly contribute to its aroma, and the commonly found halogenated compounds in various red marine macroalgae species do not thrive in this particular seaweed (except for trichloroethylene) [26; 107; 108]. These results are consistent with our findings. Regarding UL, aldehydes not only prevail as the most abundant VOCs in terms of diversity, but also exhibit the highest concentration in relation to the chromatogram area (see Supplementary Material, Figure S3). These findings align with the description provided by [PERSON] & [PERSON] [26] regarding the distinctive flavor constituents of _Ulva australis_ (formerly _Ulva pertusa_). PU showed a high concentration of 8-heptadecene (isomer 2) and heptadecene, which apparently do not influence the aroma of the samples due to their high odor thresholds [59]. The presence of these hydrocarbons may result from responses to treatments and biological activity of the marine macroalgae and associated microorganisms [26; 108]. In seaweed, 8-heptadecene is involved in a protective mechanism against mechanical damage, functioning as a chemoreception molecule and biological pheromone during the wound healing process. Some seaweeds possess an enzymatic system capable of catalyzing eicosapentaenoic acid to produce this alkene [109]. The higher occurrence of 8-heptadecene in the VAC samples appeared to be related to the damage caused by the compression of the UL during the packaging process. Numerous studies have reported the presence of heptadecane or heptadecene in \"laver\" seaweeds [106; 110; 111], including heptadecane in _P. umbilicials_[112] and 8-heptadecene in _Pyropia_ spp. [109; 113]. According to [PERSON] et al. [114], heptadecane and heptadecene were the predominant hydrocarbons found in red seaweeds collected from the Black Sea. Pentadecanl appeared to have a relevant effect on the characterization of the aromatic profile of both the CTRL and MAP-treated PU due to its high abundance and lower odor thresholds (0.715 mg/kg). Pentadecanl exhibits a refreshing, wax-like scent with hints of floral notes [115; 116]. Pentadecanl formation in seaweed seems to be related to \(\alpha\)-oxidation of palmitic acid (PA) by lipoxygenenses [117]. For some yet unknown cause, it seemed that the VAC treatment exhibited greater efficacy in inhibiting pentadecanl production. For UL, (_E,E_)-2,4-decadienal and one of its isomers were the compounds with the highest concentration, particularly in the control on day 0.