## 3 Results and Discussion
### Determination of the Lipid Content and Lipid Hydrolysis Events  
The pouting muscle showed a low lipid content (5.58 \(\pm\) 0.39 g\(\cdot\)kg\({}^{-1}\) muscle), which corresponds to a lean fish species [53]. This lipid content agrees with a previous seasonal study which indicated a 0.54-1.08 g\(\cdot\)100 g\({}^{-1}\) muscle range for the entire ground muscle (white and dark muscles altogether) of the current fish species [18]. Recently, a low lipid content (i.e., 1.0 \(\pm\) 0.1 g\(\cdot\)100 g\({}^{-1}\) muscle) was also reported for pouting by [PERSON] et al. [19].  
Lipid hydrolysis events in pouting muscle were investigated by assessing the FFA content (Figure 2). The initial FFA value was 13.4 \(\pm\) 1.0 g\(\cdot\)kg\({}^{-1}\) lipids. Afterward, remarkable increases in the FFA content (_p_ < 0.05) with the chilling time were observed (_r_ = 0.94, quadratic fitting). Notably, the FFA fraction represented approximately 17% of the total lipid fraction at the end of the study, with this value being over 10 times higher than the initial value.  
It has been signaled that FFA formation during chilled storage would occur as a result of endogenous enzyme and microbial activities [25; 27]. Before attaining the end of the microbial lag phase, FFAs are reported to be mainly produced by effect of endogenous enzyme activity (namely lipases and phospholip) [48; 49]. Then, the impact of microbial activity should increase as a result of processes related to bacterial catabolism [26; 27]. In agreement with this important role of microbial activity in FFA formation, good correlation values between the FFA values and both the aerobic mesophile and psychrotroph counts (_r_ = 0.94 in both cases) were detected in the present study.  
Although the release of FFAs themselves does not imply any remarkable loss of nutritional quality, FFA accumulation has been linked to an enhancement of lipid oxida  
Figure 1: Evolution of trimethylamine (TMA; mg TMA-N\(\cdot\)kg\({}^{-1}\) muscle) value in pouting muscle subjected to chilling storage. Average values of three independent determinations (_n_ = 3), with standard deviations denoted by bars. Different letters (a, b and c) denote differences (_p_ < 0.05) with chilling time.  
tion [54; 55] and textural deterioration due to interactions with proteins [47; 56]. Additionally, FFAs have been reported to undergo a faster oxidation rate than higher molecular weight lipid classes such as triacylglycerols and phospholipids. This differential behavior has been explained on the basis of offering a lower steric hindrance to the initial development of the oxidation mechanism [24; 57].  
To the best of our knowledge, no previous studies have addressed the FFA evolution of pouting muscle during refrigerated storage. Regarding other lean fish species, FFA formation has been shown to occur to a lesser extent in general compared with the present species. Thus, low FFA values were detected in the dorsal and ventral zones of Atlantic pomfret (_Brama brana_) [52]. After 15 days of storage, FFA contents of 3.2 and 4.6 g\(\cdot\)100 g\({}^{-1}\) lipids were observed, respectively. Hake (_M. merluccius_) muscle attained a 2.5 g\(\cdot\)100 g\({}^{-1}\) lipids range after a 19 day storage period [58]. Low FFA formation (approximately 13 g\(\cdot\)kg\({}^{-1}\) lipids) was also detected in farmed turbot (_Psetta maxima_) muscle after a 19 day period [59]. However, wild turbot (_Scophththalmus maximus_) led to notably higher FFA formation (20.6 g\(\cdot\)100 g\({}^{-1}\) lipids) after a 19 day storage period [51]. Regarding underutilized low-fat species, chilled lobster krill (_Munida_ sp.) exhibited an FFA value of 28.1 g\(\cdot\)kg\({}^{-1}\) lipids (10 days of storage) [11].