*2.8. Meat Quality*

After 1 h post-mortem, the right *Longissimus thoracis* (LT) muscle between the 7th and 11th ribs was removed from the carcass with a scalpel and used for pH, colour, Warner-Bratzler shear force (WBSF), chemical composition, drip loss and cooking loss analysis. Samples of *LT* muscle (approximately 600 g) were collected from the carcass and then frozen at −20 ◦C for a subsequent meat quality analysis.

Prior to the analysis of cooking losses (CL) and Warner-Bratzler shear force (WBSF), the samples were thawed for 24 h at 4 ◦C in a cooler protected from drafts and the meat samples were analysed in triplicate. CL was determined according by Vazquez-Mendoza et al. [33]; for this purpose, fillets with 2.5 cm thick were roasted on a grill (Toastmaster cool-edgegrill, Macon, MO, USA) until they reached an internal temperature of 70 ◦C, which was monitored with a thermometer (Brannan & Sons, Cleator Moor, Cumbria, UK). When the temperature reached 70 ◦C, the fillets were removed from the grill and allowed to cool to room temperature (20–25 ◦C). To calculate the percentage of CL, each fillet was weighed before and after the procedure (weight of raw meat −weight of cooked meat)/weight of raw meat ×100), as it was described by Vazquez-Mendoza et al. [33]. In order to measure the WBSF, 2.5 cm thick meat fillets (three per lamb) were cooked at 70 ◦C using the CL method, as sited above. WBSF was measuring using an Instron® universal testing machine (model 1132, Instron, Canton, MA, USA) with a Warner-Bratzler accessory [34]. Meat colour was determined on cuts of the *longissimus dorsi* muscle 24 h after slaughter using a Minolta CM-2006d spectrophotometer (Konica model, Minolta Holdings Inc., Osaka, Japan). Lightness (L\*), redness (a\*) and yellowness (b\*) as meat quality attributes were evaluated using the procedure described by Miltenburg et al. [35]. With the values of a\* and b\*, the Chroma (C\*) and Hue (H\*) indices were calculated using the equations: Chroma = (a\* 2 + b\* 2)0.5 and Hue = tan−<sup>1</sup> (b\*/a\*) × 57.29 both expressed in degrees [36]. Colour coordinate values were obtained using the average of three measurements of colour for each sample. Meat pH was measured following the procedure described by Negrete et al. [37]. This was measured in triplicate on 3 g of *longissimus dorsi* muscle homogenized in 20 mL of deionized water using a blender Waring 51BL32 (model 700, Torrington, CT, USA), and using a Hanna® pH meter (Model HI 98127, Waterproof Tester, Woonsocket, RI, USA). Drip loss value was calculated

as weight loss of the fresh meat sample (90 g) placed in a plastic bag after storage for 24 h at 4 ◦C. Drip loss was determined in triplicate as percentage of water released from fresh muscle [38].

Prior to the proximate analysis of meat, the samples were thawed for 24 h at 4 ◦C. The subcutaneous fat and connective tissue were separated from the muscle using a scalpel, and the meat was ground and homogenized for 5 min with a mixer. Meat samples were analysed in triplicate to determine the moisture, lipid, protein and ash content as a percentage of the muscle sample following AOAC procedures [28].
