*2.3. Colour*

The interaction between treatment and day of shelf life was not significant (*p* > 0.05). Treatment and storage time affected the colour of *L. lumborum* (*p* < 0.001). Seven d of storage in 75% O2 packs negatively affected (*p* < 0.05) a \*, b \* and c \*, decreasing the values of the three colour coordinates (Figure 3).

**Figure 3.** Colour coordinates (L\* = lightness, a\* = redness, b\* = yellowness, and C\* = Chroma. ± S.E.) in m. *Longissimus lumborum* of male lambs unsupplemented (CON) or supplemented with three different levels of oregano essential oils (LO = 0.2 g/kg of DM; MO = 0.3 g/kg of DM; or HO = 0.4 g/kg of DM) or monensin (SM), during 7 d of simulated retail display in modified atmosphere packaging (O2:CO2, 75:25%).

The value of a\* differed among treatments (*p* < 0.001). SM, MO, and the meat with a low level of OEO (LO) had the highest values during storages (Figure 3, *p* < 0.001). SM, MO, and LO had also the higher b\* values throughout storage compared to CON and HO (Figure 3). Treatment also affected C\*. In this case, SM, MO, and LO were the highest (*p* < 0.001); meanwhile, CON and HO were similar (*p* = 0.03).

These statements can be confirmed with the means of the colour coordinates by treatment (Figure 4). It can be established that the dietary addition of 0.2–0.3 g/kg dry matter (DM) OEO and SM (commercial dosage) reduces colour loss after 7 d under MAP.

**Figure 4.** Means (± S.E.) of colour coordinates (L\*, lightness; a\*, redness; b\*, yellowness; C\*, saturation) in m. *Longissimus lumborum* of male lambs unsupplemented (CON) or supplemented with three different levels of oregano essential oils (LO = 0.2 g/kg of DM; MO = 0.3 g/kg of DM; or HO = 0.4 g/kg of DM) or monensin (SM), with 7 d of simulated retail display in modified atmosphere packaging (O2:CO2, 75:25%). a,b Different superscripts mean significant difference (*p* < 0.05) among treatments.

#### *2.4. Fatty Acid Profile*

In general, the inclusion of OEO or SM affected the fatty acid profile (*p* > 0.05). Eighteen FAs were analyzed, and their percentage was calculated relative to all FAs (Table 1). Differences were observed (*p* < 0.05) among treatments in a single FA. The treatment modified the percentage of C16:1n7, C20:1n9, and C22:6n3. Furthermore, it also modified the content (mg/kg of muscle) of C14:0, C16:0, C18:0, C16:1n7, C18:1n9c, C18:1n6c, C20:1n9, and C18:2n6c (Table 2).

**Table 1.** Percentage of fatty acids in the total fat of *Longissimus lumborum* of male lambs unsupplemented (CON), supplemented with three different levels (HO = 0.4 g/kg DM; MO = 0.3 g/kg DM; LO = 0.2 g/kg DM) of oregano essential oils or supplemented with monensin (SM) at commercial doses.


a,b Different superscripts mean significant difference (*p* < 0.05) among treatments (columns).

**Table 2.** Concentration of fatty acids (mg/kg of muscle) in total fat of *Longissimus lumborum* of male lambs affected by supplementation of three different levels (HO = 0.4 g/kg DM; MO = 0.3 g/kg DM; LO = 0.2 g/kg DM) of oregano essential oils or monensin (SM) at commercial doses *vs.* a control diet (CON).


a, b Different superscripts mean significant difference (*p* < 0.05) among treatments (column) in the same fatty acid.

HO decreased the concentration of C14, C16, and C18 (*p* < 0.05); meanwhile, MO increased (*p* < 0.05) them. LO and SM did not alter the concentrations of these acids when compared to CON (*p* > 0.05, Table 2). Higher concentrations of C14, C16, C18, C16:1n7, C18:1n, C20:1n9, and C18:2n6t in the total fat of *Longissimus lumborum* were observed (*p* < 0.05) in MO meat compared to the control group.

Concentrations (Table 2) of monounsaturated fatty acids (MUFAs); C16:1n7, C18:1n9c and C20:1n9 were different among treatments (*p* < 0.05). MO increased the concentration of these MUFAs (*p* < 0.05), while HO decreased the concentrations (*p* < 0.05). HO, LO, and CON had similar low levels, whereas SM and MO had higher values (*p* < 0.05).

The treatment (*p* < 0.05) affected the concentration of linoleic acid (C18:2n6t) in total fat. MO increased concentrations of C18:2n6t (*p* < 0.05, Table 2). The lowest concentrations of C18:2 were in HO meat.
