## 2 Materials and Methods
### Volatile Compound Analysis  
The profile of meat volatile compounds was studied using the solid-phase microextraction (SPME) analysis technique. A sample (20 g) of the LTL muscle was thawed at 4 \({}^{\circ}\)C overnight before analysis and was cooked at 200 \({}^{\circ}\)C under a mixed closed griddle (Jatta electro, GR266 1000W, Abadiano, Vizcaya, Spain). The grill was switched on for 15 min before the sample was grilled. Each sample was placed in the middle of the grilling tray in order to be grilled uniformly and was cooked for approximately three minutes at a temperature of 70 \({}^{\circ}\)C [16]. Directly after cooking, the meat was chopped finely and, together with all the fat released from the steak during cooking, placed in an electric bowl chopper (Janke and Kunkel A-10, IKA Labortechnik, Germany). Straight after chopping, 10 g of the cooked sample was placed in a headspace vial (Tekmar, 100 mL) and equilibrated for 40 min at 40 \({}^{\circ}\)C prior to exposure of the SPME fibre (Fibre Assembly 50/30 \(\upmu\)m DVB/CAR/PDMS, Stableflex-2 cm-23 Ga, Gray-Notched; Bellefonte, Pensilvania, EEUU) placed over the sample for a further 20 min. The analysis of volatile compounds was performed using a Thermo Scientific TRACE 1300 series (Milan, Italy) gas chromatograph (GC) equipped with a Thermo Scientific TRIPLUS RSH autosampler (Milano, Italy) for injection and coupled with an ion trap mass spectrometer (Thermo Scientific ISQ QD Single Quadrupole Mass Spectrometer; Milan, Italy). The desorption process of the compounds was carried out using the spitless mode with purges of 5 mL/m. Injection was maintained for 10 min at a temperature of 40 \({}^{\circ}\)C. Meanwhile, the chromatograph oven was heated to 40 \({}^{\circ}\)C and, once the sample had been released into the gas phase, the temperature was increased at a rate of 5\({}^{\circ}\)C/min up to a maximum temperature of 220 \({}^{\circ}\)C. Helium at 20 psi with a flow of 1.2 mL/min at 40 \({}^{\circ}\)C as carrier gas was used. The volatile compounds were separated using a VF-WAXms fused silica capillary column (30 m length \(\times\) 0.25 mm id \(\times\) 0.50 \(\upmu\)m film thickness, Agilent Technologies, Inc. 2012, Santa Clara, CA, USA). The operating conditions were as follows: initial temperature, 40 \({}^{\circ}\)C for 5 min, then increased to 220 \({}^{\circ}\)C at a rate of 5 \({}^{\circ}\)C/min and held for 5 min, with a total acquisition time of 56 min. The temperatures of the source and quadrupole were 175 \({}^{\circ}\)C and 150 \({}^{\circ}\)C, respectively. The mass spectra of volatile compounds were generated by a MS equipped with an ion trap. The data acquisition was performed by scanning the mass range 29-400 amu. in El mode (70 eV with emission current of 50 mA) at 1.9 microscan/s. The volatile compounds were identified by comparing their mass spectra with spectra included in NIST/EPA/NIH Mass Spectral Libraries and confirmed by matching their LRI with [PERSON] et al. [17; 18] and [PERSON] et al. [19] or the Flavornet database. The linear retention indices (LRI) [20] were calculated by previous injection of standards of saturated n-alkanes (C6-C22) under the same GC-MS conditions. The volatile compounds were expressed as a percentage of the total volatile compounds identified.