## 3 Results and Discussions
### Chemical Results in HTS Fillets  
TMA basically originates from trimethylamine oxide based on the breakdown of bacterial community as well as enzymatic autolysis, which is the primary substance that contributes to the 'fishy' off-odor in aquatic products [22]. HTS fillets samples dipped in chitosan-based coating evidenced an obvious inhibitory effect on TMA formation (Figure 2a). The initial TMA value of 0.15 mg N/100 g increased to 10.5 and 9.18 mg N/100 g in CK1 and CK2 samples on final day 18,  
Figure 1: Changes in total viable bacteria (**a**), _Pseudomonas_ spp. (**b**), and H\({}_{2}\)S-producing bacteria (**c**) of half-smooth tongue sole fillets during refrigerated storage (CK1: Chitosan coating without rosmarinic acid or \(\varepsilon\)-PL; CK2: Chitosan coating with 30 mg/kg rosmarinic acid; C1/C2/C3/C4: chitosan coating with 30 mg/kg rosmarinic acid and 0.05%/0.10%/0.15%/0.20% \(\varepsilon\)-PL). respectively. However, the treated HTS samples resulted in significantly lower (\(p<0.05\)) values of 2.25, 1.50, 1.51, and 1.53 mg N/100 g for C1, C2, C3, and C4 after 18 days storage, respectively. The use of chitosan-based coating combined with \(\varepsilon\)-PL and RA led to a sharp reduction in the TMA formation in the HTS fillets. According to [PERSON] et al., a TMA value of 10 mg N/100 g has been used as a limit value of fish freshness [23]. Based on our research (in all treated samples, day 15), a TMA value of 5 mg N/100 g could be considered as an indication of HTS fillets spoilage initiation, and such value in our study corresponded to the microbiological TVC limit value of 7 log CFU/g at day 15 (Figure 1a). The TMA formation was mainly caused by spoilage organisms in HTS fillets, such as _Pseudomonas_ spp- and H\({}_{2}\)S-producing bacteria. The lower TMA values in treated samples could be the result of bacterial inhibition by chitosan-based coatings containing \(\varepsilon\)-PL and RA. Notable TVB-N formation was also determined in HTS fillets under study (Figure 2b). This increase was especially apparent in CK1 and CK2. High TVB-N values in aquatic products during storage demonstrate that nitrogenous materials accumulated from the degradation, operated by proteolytic bacteria of nitrogenous-containing molecules, such as proteins and nucleic acids [24]. \(\varepsilon\)-PL and RA significantly reduced the formation of TVB-N compared to CK1 and CK2 samples. TVB-N values slowly increased from an initial value of about 10 mg N/100 g of HTS fillets at day 0 to 31.52 and  
Figure 2: Changes in trimethylamine (TMA, **a**), total volatile basic nitrogen values (TVB-N, **b**), inosine 5\({}^{\prime}\)-monophosphate (IMP, **c**), hypoxanthine (Hx, **d**), **K** value (**e**), and Thiobarbituric acid (TBA, **f**) of half-smooth tongue sole fillets during refrigerated storage (CK1: Chitosan coating without rosmarinic acid or \(\varepsilon\)-PL; CK2: Chitosan coating with 30 mg/kg rosmarinic acid; C1/C2/C3/C4: Chitosan coating with 30 mg/kg rosmarinic acid and 0.05%/0.10%/0.15%/0.20% \(\varepsilon\)-PL). 30.03 mg N/100 g at day 18 for CK1 and CK2 samples, respectively; however, the treated samples (C1, C2, C3, and C4) reached 18.13, 15.26, 14.91, and 13.14 mg N/100 g, respectively. These treated HTS fillets values are below the rejection limit of TVB-N content (30 mg N/100 g) for marine fish. Changes in IMP, Hx, and \(K\) values of HTS fillets samples are shown in Figure 2c-e. IMP provides a sweet and meaty flavor that contributes to enhancing fish quality, whereas its conversion in Hx is responsible for unpleasant bitterness [25]. The IMP concentrations increased first and then decreased with storage time in all samples (Figure 2c). The concentrations of IMP in the CK1, CK2, C1, C2, C3, and C4 samples were at a maximum level at day 3 with values of 8.53, 8.29, 8.17, 7.83, 7.94, and 8.01 mmol/kg, respectively.