*3.3. Meat Quality Traits*

The significance of factors of variations on meat quality parameters of the LT muscle is reported in Table S3. The interaction between measuring time and genetic type was significant for all colour coordinates and for shear force.

Post mortem pH decline (Figure 2a) was similar between genetic types although a significant (*p* < 0.05) decrease was reported in the first 6 h after slaughter, which stabilized during subsequent measurements. A similar pH trend was observed by Shen et al. [40] when comparing local Chinese breeds and crossbreeds of pigs.

L\* (lightness) measured at 6, 24, 72, and 144 h after slaughter increased progressively as post mortem time increased (Figure 2b). The L\* values measured in the meat of Apulo-Calabrese were significantly lower (*p* < 0.05) than those recorded in the meat of crossbreeds in all measuring times, with the exception of those recorded at 144 h after slaughter. The L\* coordinate in the meat of crossbreeds stabilized after 24 h whilst that of Apulo-Calabrese maintained an almost constant increase. According to Scheffler and Gerrard [41] post mortem pH can affect muscle colour. Despite the similar levels of pH in this experiment significantly higher (*p* < 0.05) values of a\* (Figure 2c) were found in Apulo-Calabrese at each detection time. This indicates that the meat from this breed is distinguished by a deeper red colour like other local European pig breeds [17,42,43]. The trend of the a\* coordinate in Apulo-Calabrese pigs showed limited variations and the only value that was significantly different from the others was that measured at 24 h post mortem. The b\* value did not differ between the two genetic types as shown in Figure 2d. For both breeds the highest b\* values were recorded at 72 h post mortem, while the value decreased significantly at 144 h post mortem.

**Figure 2.** Changes in pH (**a**) and colour coordinates (L\* in (**b**), a\* in (**c**) and b\* in (**d**)) in *longissimus thoracis* in Apulo-Calabrese and crossbreed pigs over time. Different letters in the graphs (a, b, c, d) indicate significant effects (*p* < 0.05).

Higher values of cooking losses were reported for both genetic types at 24 h post mortem (Figure 3a) compared to lower values recorded at 72 and 144 h after slaughter. Apulo-Calabrese pigs showed slightly higher values at 24 h post mortem compared to crossbreeds, but these differences did not reach statistical significance. Apulo-Calabrese showed lower values of cooking loss when compared with the values of other local breeds, like Cinta Senese [44] and Nero Siciliano [45]. There was no effect of genetic type on drip loss (4.19 ± 0.2 and 4.78 ± 0.2 for Apulo-Calabrese and crossbreeds, respectively).

Warner-Bratzler shear force measured after drip and cooking loss (Figure 3b) decreased as post mortem time increased and showed a similar trend in both genetic types. Nevertheless, higher values were reported for Apulo-Calabrese at 24 and 144 h after slaughter, suggesting the need to subject the meat of Apulo-Calabrese to ageing if it is intended for fresh consumption.

Figure 4 reports the results of the PCA performed on meat quality traits. Multivariate analysis generated four PCs: PC1, PC2, PC3, and PC4 explained 25%, 14%, 9%, and 8% of the total variance, respectively. The component that explained the most differences between the two genetic types was PC2, since samples displayed to be clustered for PC2 (Figure 4a). Figure 4b graphically displays PCA loadings, numerically presented in Table S4.

**Figure 3.** Changes in cooking loss (**a**) and shear force (**b**) in the *longissimus thoracis* in Apulo-Calabrese and crossbreed pigs over time. Different letters in the graphs (a, b, c) indicate significant effects (*p* < 0.05).

**Figure 4.** Results of principal components analysis (PCA) on the meat quality traits: (**a**) score plots for principal component 1 (t1) and principal component 2 (t2) of Apulo-Calabrese (blue) and crossbreeds (red) samples; (**b**) loadings plot with the weights of variables included in principal component 1 (p1) and principal component 2 (p2).

The variables that weighted most in PC2 were colour coordinates a\* at 24 h (−0.409), a\* at 6 h (−0.394), a\* at 72 h (−0.368), a\* at 144 h (−0.363), L\* at 72 h (−0.257), and pH measured at 24 h (0.276). The high weights observed for a\* colour coordinate are in agreemen<sup>t</sup> with the significant differences obtained from univariate analysis reported in Figure 2c, where redness-greenness value a\* was highly divergent at all the measuring times between the two pig genetic types. Together with a\*, other variables that contribute in differentiating the two genetic types were L\* and pH, as can be noticed both by PCA loadings in Figure 4b and Table S4 and by mixed model results in Table S3. Interestingly, despite the different statistical assumptions of mixed and multivariate analysis, the results obtained are quite concordant, highlighting that colour coordinates represents the meat quality attributes discriminating the most the two genetic types. Anyway, PCA results suggested that, when considering together all the meat quality variables and taking into account their correlated nature, also pH measured at 24 h has a consistent weight in differentiating Apulo-Calabrese from crossbreed pigs. This result may also be noticed in Table S3, from the mixed model results. Despite the genetic type had not a significant effect on *longissimus thoracis* pH, the estimated L.S.M. for pH at 24 h were the most divergent between the two genetic types (5.57 for Apulo-Calabrese and 5.45 for crossbreeds) when compared with the pH measured at the other times. This result suggests that using a combined statistical approach may allow to highlight the main differences that would have not been appreciable with the use of univariate statistics alone.
