## 4 Discussion
Additionally, 2- and 3-methyl-1-butanol, ethanol, 2- and 3-methylbutanal, 3-hydroxy-2-butanone, acetic acid, dimethyl sulfide, 3-methylbutyl acetate and various ethyl esters were associated with _Pseudomonas_ in FJA models of gilt-head sea bream stored at 0 and 15 \({}^{\circ}\)C [15]. Here, it is important to underline the production of such esters by _Pseudomonas_ spp. (through esterase activity) in seafood during storage [2]. In real seafood, such VOC were also detected, and increased in some cases, in gilt-head sea bream, European sea bass and meagre, at various chilled storage conditions where _Pseudomonas_ spp. dominated [6; 7; 8; 21]. Indeed, many of these compounds can be produced by the catabolism of aminoacids or other compounds of substrate by _Pseudomonas_ spp. [13]. On the other hand, the compounds detected in both inoculated and non-inoculated models (e.g., 2-ethyl-1-hexanol, 1-penten-3-ol, 2-hexen-1-ol (trans), nonanal, n-decanal, heptanal, octanal, hexenal, 6-methyl-5-hepten-2-one, acetophenone, etc.) cannot be clearly related to microbial or chemical activity. For example, 2-ethyl-1-hexanol has been found to be linked with the activity of lactic acid bacteria in sterile shrimp [28] and FJA models [15]; however, it has also been reported as a non-microbial origin compound [15]. On the other hand, the rest of the aforementioned compounds, e.g., 1-penten-3-ol, heptanal, nonanal, etc., have already been reported to be products of chemical activity in seafood; in particular, they are involved in the oxidative reactivity of polyunsaturated fatty acids [29; 30; 31]. Our findings indicate that different storage temperatures affect, to some extent, the metabolic profile of the strains. Indeed, the interactive behavior of microorganisms in seafood not only contributes to their growth, but also their spoilage activity [26]. Some of the compounds of microbial origin presented an increasing tendency during FJA storage, and so might be used as CSIs of the freshness or spoilage status of seafood. Among them, some compounds (e.g., methanethiol, dimethyl sulfide, dimethyl disulfide, 2-pentanone, ethyl acetate, 2-nonanone, n-nonanone, 2-undecanone, 3-octen-2-one, 2-heptanone) were associated with some of the _Pseudomonas_ strains (e.g., 35, 35, 55), other compounds were associated with all strains (e.g., 2-heptanone), while others (e.g., hexyl acetate, ethyl-2 methylbutyrate, ethyl isovalerate, ethyl isobutyrate) were associated with the action of one strain only (e.g., 61), revealing the spoilage activity of the different strains of _Pseudomonas_. The majority of these compounds were associated with quality deterioration due to the development of off-odors and off-flavors in chill-stored seafood [2]. Indeed, such compounds, mainly the ethyl esters, have also been found to increase in gutted gilt-headsea bream and European sea bass during storage at 2\({}^{\circ}\)C where _P. fluorescens_ dominated [6; 7], and in gilthead sea bream fillets at 0 and/or 5 under air where _Pseudomonas_ genus in general dominated [21]. In all these cases, sensory rejection occurred when _Pseudomonas_ reached spoilage level (8-9 log cfu/g), and in parallel, some of the aforementioned compounds increased. Taking into account all information and findings, the compounds of microbial origin found herein could indeed be used as potential CSIs in some seafood, such as aerobically stored Mediterranean aquacultured fish.