2.2.1. Samples Elaboration

Ultrafrozen skinless hake fillets (*Merluccius capensis, Merluccius paradoxus*) (Pescanova España S.L.U.) were bought in a local supermarket and thawed in refrigeration for 24 h before making into fish patties. Fish was minced in an electric mincer (Bosch, Germany) for 2 min, mixing all the ingredients of each one of seven samples, represented in Table 1. Afterwards, fish patties were formed (50 g) and packed in aerobic conditions. Samples were stored at 4 ◦C until analysis, at day 0, 4, 7 and 11. 20 fish patties were formed for each batch and analysis were carried out by triplicated.

**Table 1.** Fish patties formulation.


Commercial mix®: supplied by Catalina Food Solutions, S.L. (El Palmar, Murcia, Spain) and composed by: vegetables fibers, salt, potato starch, stabiliser (Pocessed euchema seaweed (PES) E-407-a), acidity correctors (sodium citrate E-331, and sodium acetate E-262), spices, spice extracts and antioxidant (sodium ascorbate E-301). P: Pomegranate extract, RA: Rosemary extract rich in Rosmarinic Acid; NOS: Rosemary extract rich in diterpenes; NOVS: Rosemary extract rich in diterpenes and with lecitin as emulsifier; HYT-L: Hydroxytyrosol extract obtained from olive leaf; HYT-F: Hydroxytyrosol extract obtained from olive fruit.

#### 2.2.2. Volatile Organic Compounds Analysis

Lipid oxidation was related with the concentration of volatile organic compounds (VOCs). For that, 5 g of fish burger samples were placed in glass vials. Volatile compounds were extracted using solid-phase microextraction (SPME). A SPME device (Supelco, Bellefonte, PA, USA) containing a fused-silica fibre (10 mm length) was used. Extraction was performed at 35 ◦C for 30 min. Once sampling was finished, the fibre was withdrawn into the needle and transferred to the injection port of the gas chromatograph-mass spectrometer (GC-MS) system. Volatiles were analysed in duplicate in all samples at days 0 and 11 from elaboration. Analyses were performed on a Hewlett-Packard 6890 N Series GC gas chromatograph fitted with a HP 5973 mass spectrometer and an MSD Chemstation (Hewlett-Packard, Palo Alto, CA, USA). A split injection port was used to thermally desorb the volatiles from the SPME fibre onto the front of the DB-624 capillary column (J&W scientific: 30 m × 0.25 mm id, 1.4 μm film thickness). Helium was used as a carrier gas with a linear velocity of 36 cm/s. The temperature programme was: 40 ◦C for 2 min and then raised to 100 ◦C at 3 ◦C/min; then from 100 to 180 ◦C at 5 ◦C/min; total run time 50.8 min. The mass spectra were obtained using a mass selective detector working in electronic impact at 70 eV, with a multiplier voltage of 1953 V and collecting data at a rate of 6.34 scans/s over the range *m*/*z* 40–300. Compounds

were identified by comparing their mass spectra with those contained in the NIST05 (National Institute of Standards and Technology, Gaithersburg) library.
