3.1. Proximate Composition
No significant differences were found in the moisture (water) content, ash content and energy value of the meat of the genetic groups of the evaluated pigs. However, significant differences were found in intramuscular fat content (
Table 2). The lowest (
p < 0.01) fat content was found in both muscles of the Puławska breed rearing pigs (1.36% in LL and 1.50% in SM), while the highest was found in the DanBred fattening pigs (2.67% in LL and 2.91% in SM). It is worth mentioning that there was a trend (
p < 0.1) of higher protein content in meat from the pigs of Puławska breed compared to that of the meat from the rearing pigs of the other groups. Consequently, the meat from the Puławska breed was characterised by the (
p ≤ 0.01) highest value of the NQI for protein and with the (
p ≤ 0.01) lowest value for fat. The average moisture content of both evaluated muscles, regardless of genetic group, was within the range typical of meat from domestic breeds of pigs (73.1–75.3%) [
9]. Babicz et al. [
26] found in the meat of fattening pigs of the Puławska breed a chemical composition similar to that obtained in the presented study for both m.l.l. and m.sm. Kasprzyk and Bogucka [
27] reported a higher fat content (2.73%) but lower protein content (22.90%) in
Longissimus lumborum of fattening pigs of the Puławska breed, while for DanBred hybrids they obtained a similar level of fat (2.50%) to that in their study and a lower protein content (20.85%) compared to that in their study, although it should be noted that the quoted results were obtained for pigs with slaughter weights ranging from 103 to 105 kg. For PUL × PLW hybrids fattened for 99 days to a weight of 103.4 kg, Milczarek et al. [
14] report a fat content in the loin (
Longissimus dorsi) of 1.76% and a protein content of 23.70%, while in ham (
Adductor) it was 2.11% and 22.81%, respectively, i.e., there was less fat and more protein compared to the values obtained in their own study for this group of hybrids of native breeds.
In Poland, it is assumed that the intramuscular fat content required for the optimum taste and flavour of meat should be between 2.5 and 3% [
28,
29]. In the study presented here, particularly in the meat of pigs of the Puławska breed, the level of intramuscular fat was significantly lower than recommended, which was related to the slaughter weight being too low for this native breed. However, previous studies have shown that meat from the pigs of the PUL breed with typical intramuscular fat content showed good oxidative stability and was suitable for 14 days of maturing under vacuum conditions [
30].
3.2. Fatty Acids
The nutritional value of fat is determined primarily by the type and content of the individual fatty acid groups. In LL, the genetic group significantly differentiated the content of major saturated fatty acids (C14:0, C16:0 and C18:0) and their total content, as well as the content of monounsaturated FAs (C16:1
n-7 and C18:1
n-9) and their sum (
Table 3). Identical relationships were also found in the SM (
Table 4). Indeed, the highest content of SFAs and MUFAs was found in the LL of DAN hybrids, while it was 2–2.5 times lower in PUL pigs, which is particularly favourable for proatherogenic FAs such as myristic and palmitic FAs. In contrast, the genetic group did not significantly affect the content of polyunsaturated FAs, including the
n-3 and
n-6 PUFAs, in both of the muscles evaluated. The fatty acid content of LL was not significantly different between PUL pigs and PLW × PUL hybrids (
Table 3), while in SM all differences (except C20:1
n-9) were found to be significant.
Milczarek et al. [
14] showed no significant differences in the fatty acid profile of the loin and ham of domestic hybrid breeds (Puławska × Polish Large White and Polish Landrace × Polish Large White). However, many authors indicate that the breed of pig significantly differentiates the fatty acid composition of muscle tissue [
31], with meat from slower-growing pigs showing a more favourable fatty acid profile, manifesting in particular as a higher proportion of PUFAs [
32].
Currently, a number of indicators are used to assess the health-promoting values of fats and the potential beneficial effects of their consumption in humans [
33]. The lower SFA content in intramuscular fat of LL (
Table 3) and SM (
Table 4) of PUL pigs determined a significantly (
p ≤ 0.05) more favourable PUFA/SFA ratio (0.20 and 0.30, respectively) compared to that of PLW × PUL hybrids (0.14 and 0.17) and DAN hybrids (0.06 and 0.18), although it did not reach the recommended level of 0.4 [
34]. In contrast, Milczarek and Osek [
35] in a study on PUL pigs fattened to a weight of 116 kg obtained a much lower value for the PUFA/SFA ratio, i.e., that for LL was in the range of 0.057–0.064, and that for SM was 0.055–0.058. Higher values for this ratio (in the range of 0.36–0.50) were reported by Choi et al. [
13] for the
Longissimus thoracis (LT) of purebred pigs and LYD (Landrace × Yorkshire × Duroc) three-breed hybrids with a slaughter weight of 110–114 kg.
In the present study, the PUFA
n-6/
n-3 intramuscular fat ratios of all genetic groups assessed were found to be very high. Choi et al. [
13] report values of this ratio similar to those obtained in the present study for the
Longissimus thoracis of purebred pigs (about 20.7) and LYD three-breed hybrids (about 18.6). Significantly lower levels of the
n-6/
n-3 ratio are reported by Kasprzyk et al. [
36] for the
Longissimus thoracis and
lumborum (LTL) of PUL breed fattening pigs (12.68) and PLW pigs (15.61). It is worth noting that, despite the widespread use of this indicator to assess the health-promoting value of lipids, it is currently subject to criticism pointing to its theoretical and practical limitations [
37,
38].
Significantly (
p ≤ 0.05) lower and thus more favourable values of the atherogenic and thrombogenic indices were found for the intramuscular fat of both PUL pig muscles evaluated (0.50 and 1.24 for LL and 0.46 and 1.13 for SM, respectively) compared to that of the other genetic groups, which was related to the several-fold lower content of saturated acids, especially C14:0 and C16:0 (
Table 3 and
Table 4). For the
Longissimus dorsi of DanBred × PIC terminal line hybrids, Alvarenga et al. [
39] reported PUFA/SFA ratio values ranging from 0.46 to 0.48,
n-6/
n-3 ratio values ranging from 2.25 to 2.80 and AI values ranging from 0.27 to 0.31. Kasprzyk et al. [
36], for lipids from the LTL of PUL fattening pigs, obtained an average AI value of 0.46 and TI value of 1.12, while for PLW pigs they obtained values of 0.46 and 1.14, respectively. Although different AI and TI levels for fats with potential beneficial effects on human health are reported in the literature, no values for these indices are currently officially recommended [
33]. It is generally accepted that consumption of lipid-containing foods characterised by lower levels of AI and TI can reduce the risk of coronary heart disease [
24].
3.3. Amino Acids
Statistical analysis of the amino acid content of the protein from the skeletal muscles assessed showed a very limited effect of the genetic group of the rearing pigs. In the case of LL (
Table 5), significant (
p ≤ 0.05) differences were found in serine, histidine and lysine content, with the highest lysine and serine content being found in PLW × PUL hybrids and the highest histidine content being found in PUL pigs. The protein of the fattening pigs of these two breed groups also contained the most IAA (indispensable amino acids).
In contrast, for the semimembranosus muscle, significantly (
p ≤ 0.01), the most histidine was found in PUL pigs (
Table 6), which also had the highest IAA content.
In general, the amino acid composition of meat from domestic animals has been known for a long time [
40], obviously subject to modifications related to the influence of factors such as species, breed, age or muscle location, and processing [
41]. In their analysis of amino acid content of the longissimus muscle of pigs of two genetic lines (faster-growing G1, with low fat, vs. slower-growing G2, with a higher fat content), Wilkinson et al. [
42] found significant differences only for serine, isoleucine and histidine. In contrast, Zhang et al. [
43] showed a significant variation in the amino acid content of the longissimus muscle of five pig breeds most commonly consumed in China. Comparing the results of the amino acid composition obtained in the presented study for LL with those reported by the cited authors, it can be concluded that the Chinese pork was characterised by a lower content of Glu (32.5–37.4), Ala (11.6–13.2), Pro (6.7–7.9), Thr (9.5–11.0), Val (10.1–11.5), Met (5.9–6.8), Tyr (8.3–9.4) and Phe (8.8–10.0). The range of the other amino acids (except for the higher concentration of His 9.8–12.2) was very similar to that in the results obtained in the presented study.