3.3. Fatty Acid Profiles and Health Indexes of Groin, Jowl, and Trimming Shoulder Fats
In
Table 4, the percentage composition of fatty acids in groups of the tested pork fats is presented. Three main groups of fatty acids were identified: monounsaturated fatty acids (MUFA), polyunsaturated fatty acids (PUFA), and saturated fatty acids (SUFA) in fats extracted from groin, jowl, and trimming shoulder of pigs fed liquid and dry diets. MUFAs were the main group of fatty acids found in groin, jowl, and trimming shoulder fats, their average share ranged from 46.11% ± 3.03 for GF_L to 52.15% ± 4.14 for TSF_L. The highest MUFA share was found in trimming shoulder fat of pigs fed a liquid diet. In the case of groin fat, no statistically significant differences were found between the average MUFA share in fat of liquid-fed (46.11% ± 3.03) and dry-fed (46.50% ± 2.84) pigs. The type of feed influenced the MUFA content in jowl fat and trimming shoulder fat. In both cases, the fats of pigs offered liquid feed (JF_L and TSF_L) were characterized by a higher MUFA percentage content. The greatest influence of the type of diet was found in the share of MUFA in trimming shoulder fat. The fat of pigs fed liquid feed (TSF_L) contained 10.72% more MUFA than the fat of pigs offered dry feed (TSF_D).
Saturated fatty acids (SFA) were the second group of fatty acids in terms of average percentage content in the fatty acid groups. The highest SFA share was found in the groin fat of liquid-fed pigs (43.11% ± 1.32), and the lowest in the jowl fat of pigs fed a dry diet (35.89% ± 0.86). Groin and jowl fats extracted from pigs fed dry feed (GF_D, JF_D) contained less SFA than fats from pigs offered liquid feed (GF_L and JF_L). The opposite result was reported in the case of trimming shoulder fat—the fat of pigs offered liquid feed was characterized by a lower SFA share. The consumption of saturated fatty acids, according to the FAO/WHO dietary recommendations [
40], should be less than 10% of the daily energy. The high consumption of these fatty acids may lead to the development of diseases such as obesity, circulatory system disorders, and digestive system cancers. Therefore, it is very important to modify the pigs diet to replace saturated fatty acids in the diet with mono- and polyunsaturated fatty acids.
It is worth emphasizing that the type of feed system influenced the average percentage content of PUFA in all three types of fat. The average PUFA content in groin, jowl and trimming shoulder fats ranged from 10.78% ± 1.02 for GF_L to 13.67% ± 1.89 for TSF_D. A higher PUFA content was found in fat extracted from dry-fed pigs compared to the fat of pigs fed a liquid diet. Alonso et al. [
41] examined the influence of fat in the diet of fattened pigs on the quality of meat, the profile of fatty acids and the sensory quality of pork. The following feed systems were used in the study: control, with the addition of animal fat, soybean oil (1%) and calcium soaps from palm oil (1%). In the intramuscular fat of pigs fed a soybean-oil-supplemented diet, the average SFA content was 34.64%, MUFA content was 45.66%, and PUFA content was 18.45%. Lu et al. [
42] conducted research on the effect of soy addition on the fatty acid profile of pork fat. In their research, soybean meal (18.60%) and soybean oil (3%) were used in pigs’ diets. The average SFA content reached 34.97%. This value was consistent with the result obtained in this study for the jowl fat of pigs fed dry feed (JF_D). In the research conducted by Lu et al. [
42], the PUFA content (16.31%) was higher than the values found in this study in the case of groin, jowl, and trimming shoulder fats, for which the PUFA share did not exceed 14%.
In
Table 4, the results determining the ratio of fatty acids from the
n-6 to
n-3 families in groin fat, jowl fat, and trimming shoulder fat are presented. Pork fats of pigs fed a liquid diet are characterized by a lower ratio of
n-6 to
n-3 fatty acids than the fats of dry-fed pigs. In fats extracted from groin and trimming shoulder fats, statistically significant differences were found depending on the feed type. The greatest difference in the
n-6 to
n-3 ratio was observed in the trimming shoulder fat. In the case of fat of pigs fed a liquid diet, it reached 8.57, and fed dry feed—11.01. In studies conducted by Alonso et al. [
41], in intramuscular fat of pigs fed a diet with the addition of 1% soybean fat, the
n-6 to
n-3 ratio of 11.03 was reported. This result is in agreement with the value obtained in this study for TSF_D. For jowl and groin fats (dry feed), the values of
n-6 to
n-3 fatty acids ratio were lower: 10.54 and 10.37, respectively. According to the recommendations, the ratio of
n-6 to
n-3 fatty acids should be less than 5:1; unfortunately, in the daily diet of Europeans, this proportion is much higher and amounts even to 15–20:1. Therefore, groin, jowl and trimming shoulder fats of liquid-fed pigs, characterized by a lower
n-6 to
n-3 fatty acid ratio, can be considered as more beneficial from a health point of view than the fats of pigs offered dry feed.
Based on the results obtained for groin, jowl, and trimming shoulder fats referring to health indices—such as the atherogenicity index (IA), thrombogenicity index (IT), hypocholesterolemic/hypercholesterolemic ratio (HH), and health-promoting index (HPI) (
Table 4)—it can be stated that no significant effect of the diet used on health indices values was observed. The lowest atherogenic index was calculated for JF_D (IA = 0.44), whereas the highest value of IA was observed for GF_L (IA = 0.57). The IA has been widely used for evaluating seaweeds, crops, meat, fish and dairy products. In the case of meat samples, the IA reached values ranging from 0.165 to 1.320, depending on the meat type. Mir et al. [
43] studied the properties of chicken (Caribro Vishal) meat and reported IA indexes reaching values from 0.165 to 0.634. The authors demonstrated the significant impact of a flaxseed-oil-supplemented diet on the lowering of IA value. Salvatori et al. [
44] calculated IA for two different lamb types (Gentile di Puglia and Sopravissana) and reported the values from 0.99 to 1.32. In the case of the intramuscular fat of the Longissimus dorsi muscle of high- and low-birth-weight pigs at 150 days of age, the IA reached values within the range of 0.27–0.31 [
45]. Considering the thrombogenicity index, the lowest value was found for JF_D (IT = 1.01) and the highest value for GF_L (IT = 1.35). The obtained IT values are in agreement with the results presented by other authors. Majdoub-Mathlouthi et al. [
46] reported, that in the case of Barbarine lambs reared on rangelands or indoors on hay and concentrate, IT reached values within the range of 1.10–1.15. In the study of Wójciak et al. [
47], the influence of sonication on the oxidative stability and nutritional value of organic dry-fermented beef was examined. The authors reported that IT for testes samples reached the values 1.10–1.34. In the present study, the jowl fat of pig-fed dry feed was characterized by the highest value of the HH index (HH = 2.51), whereas in the case of groin fat (liquid feed) the lowest value of that index (HH = 1.99) was calculated. Similar results were reported by other authors for chicken meat (HH—2.658–2.786) [
48], lamb meat (HH = 1.92) [
33], and beef cattle meat (HH = 1.56–2.08) [
49]. HPI calculated for studied fats reached values from 1.75 for GF_L to 2.27 for JF_D. The obtained results are similar to those obtained for intramuscular lipids of the longissimus thoracis muscle from pigs receiving a diet with different
n-6/
n-3 PUFA ratios. The authors reported HPI values of 2.21 and 2.23 in the case of diets with a low
n-6/
n-3 PUFA ratio (1.4:1) and high
n-6/
n-3 PUFA ratio (9.7:1), respectively [
50]. Dal Bosco et al. [
51] studied the nutritional indexes of the breast meat of two poultry genotypes with different growth rates—slow-growing (SG, growth rhythm < 20 g/d) and fast-growing (FG, growth rhythm > 40 g/d)—and calculated HPI values for SG and FG chickens of 1.81 and 1.59, respectively.
It is worth mentioning that both IA and IT can provide information regarding the potential impact of individual fatty acids on the likelihood of atherosclerosis occurrence and the tendency for thrombus and clot formation in blood vessels. Fats characterized by lower IA and IT values are thought to have beneficial health effects due to minimizing the risk of cardiovascular diseases. Special attention should be paid to fats with IA values below 1.0 and IT values below 0.5 as they are particularly desirable for human nutrition [
52,
53]. Based on the obtained results, it can be summarized that in the case of studied pork fats, all samples were characterized by IA lower than 1.0, but IT was found to exceed the recommended value, which can have consequences for the increased risk of clot formation in the blood vessels and cardiovascular disease.
In
Table 5,
Table 6 and
Table 7, the share of selected fatty acids in pork fat of the groin, jowl and trimming shoulder is shown. In the analyzed fats, the dominant fatty acid was oleic acid (C18:1
n-9), its share ranged from 42.30% for GF_L to 48.10% for TSF_L. Another fatty acid found in significant amounts was palmitic acid (C16:0) with a percentage content ranging from 22.07% for JF_L to 25.16% for GF_D. The most abundant PUFA was linoleic acid (C18:2
n-6) (8.91% for TSF_L—11.87% for TSF_D).
An influence of the feeding type on the content of linoleic acid (C18:2
n-6) was found in groin fat (
Table 5). In the case of fat of pigs fed a liquid diet, the average content of linoleic acid was 9.17%, and in dry feeding system—it was higher (10.44%). In groin fat, the feeding system had no effect on the content of the following acids: myristic (C14:0), palmitic (C16:0), stearic (C18:0), and oleic (C18:1). The share of oleic fatty acid (C18:1) in the groin fat of pigs fed liquid or dry feed reached 42.30% and 42.66%, respectively. Lu et al. [
42] reported a similar oleic acid content in their research. The fat of pigs fed a diet containing soybean raw materials contained 42.40% of oleic acid.
In the case of jowl fat, oleic acid (C18:1) was the dominant fatty acid (
Table 6). In the fat of pigs fed liquid feed, its average content was higher (47.83%) than in the fat of pigs fed a dry diet (46.93%). Alonso et al. [
41] determined a similar content (45.58%) of oleic acid in their studies. There was no statistically significant effect of the feed type on the content of palmitic acid (C16:0). The content of palmitic acid in the tested fats was very similar to the values obtained by Alonso et al. [
41] (22.15%) and by Lu et al. [
42] (21.94%). The percentage content of myristic (C14:0) and stearic (C18:0) acids was higher in pork fat of pigs fed liquid feed than in the fat of pigs offered dry feed. It is worth mentioning that the feed type had an influence on the share of linoleic acid (18:2
n-6), which was present in higher amounts in the jowl fat of dry-fed pigs.
In the pork fat of trimming shoulder, the greatest influence of the feeding type on the content of fatty acids was found (
Table 7). The share of MUFA was higher in the case of pork fat of pigs fed a liquid diet. The fat of liquid-fed pigs contained 48.1% oleic acid (C18:1), while the fat of pigs fed dry feed contained 42.81%. The difference in the oleic acid percentage content in these two fat samples (TSF_L and TSF_D) was statistically significant. Lu et al. [
42] reported a very similar content of oleic acid (42.40%) as in this study for fat of pigs offered dry feed. The saturated fatty acids found in large amounts in trimming shoulder fat were palmitic acid (C16:0) and stearic acid (C18:0). The content of these fatty acids was lower in pork fat of pigs fed a liquid diet. In the study conducted by Lu et al. [
42], the percentage composition of fatty acids in pork fat was similar to that reported in this study. According to Lu et al. [
42], the highest content of oleic fatty acid (C18:1) (42.40%) was found in the pork fat of pigs fed a diet containing soy raw materials. A high content of palmitic acid (C16:0) was also found (24.28%). In the research conducted by Lu et al. [
42], the content of linoleic acid (C18:2
n-6) was higher than that found in this study and amounted to 13.66%. In this study, in the tested jowl, groin, and trimming shoulder fats, the content of linoleic acid did not exceed 12%. Notably, in the case of trimming shoulder fat, a higher share of linoleic acid was found when a dry feeding system was applied.
3.4. Distribution of Fatty Acids between Internal (sn-2) and External (sn-1,3) Positions of Triacylglycerols in Groin, Jowl, and Trimming Shoulder Fats
In
Table 5,
Table 6 and
Table 7, the distribution of selected fatty acids in the internal (
sn-2) and external (
sn-1,3) positions of triacylglycerols (TAG) of groin, jowl, and trimming shoulder fats, as well as the share of individual acids in the internal position, are presented.
In groin fat, the highest content of palmitic acid (C16:0) was found in the
sn-2 position, 61.67% and 62.14% in the case of fat extracted from the groin of pigs fed liquid and dry feed, respectively (
Table 5). The share of this fatty acid in the
sn-2 position in the groin fat of pigs offered liquid feed was 84.04%, and it was higher than in the case of the dry feeding system (82.32%). In the fat extracted from pigs fed liquid feed, the lowest amount of stearic acid (C18:0) was found in the
sn-2 position, and its share in this position reached 10.93%. However, in the fat of dry-fed pigs, the lowest amount of myristic acid (C14:0) was determined in the
sn-2 position, and its share in internal position was similar to that of palmitic acid (C16:0). The share of linoleic acid (C18:2
n-6) in the
sn-2 position was higher in triacylglycerols of pork fat of pigs fed a liquid diet (19.77%) than in the triacylglycerols of fat of pigs offered dry feed (17.52%).
In the case of jowl fat, the dominant acid in the
sn-2 position was palmitic acid (C16:0) (
Table 6). In the triacylglycerol molecules of fat of dry-fed pigs, a higher content of palmitic acid was found in the
sn-2 position—59.03%, than in the fat of pigs fed a liquid diet—57.49%. The share of this fatty acid in the
sn-2 position of triacylglycerols in the case of both fats was approximately 88%. Based on the obtained results, it can be stated that palmitic acid (C16:0) was mainly located in the internal position in the triacylglycerol molecule and unsaturated fatty acids (oleic acid and linoleic acid) occupied mainly external positions in triacylglycerol molecules as their share in the
sn-2 position was not high.
In the pork fat extracted from trimming shoulder fat (
Table 7), as in the case of groin and jowl fats, palmitic acid (C16:0) was most abundant in the
sn-2 position. Its share in internal position reached 84.35% for TSF_L and 82.29% for TSF_D. The share of unsaturated fatty acids in the
sn-2 position was much lower—in the case of oleic acid, it reached 14.44% for TSF_L and 14.43% for TSF_D. Considering the share of linoleic acid, it can be observed that 21.29% and 19.29% of this fatty acid was esterified in the
sn-2 position in TSF_L and TSF_D samples, respectively. Taking the above into consideration, it can be concluded that in the studied fats, unsaturated fatty acids were mainly located in the external positions of triacylglycerol molecules.
Summarizing the obtained results regarding the distribution of selected fatty acids in the internal (
sn-2) and external (
sn-1,3) positions of triacylglycerols of groin, jowl, and trimming shoulder fats and the share of individual fatty acids in the internal
(sn-2) position, it can be stated that the internal position in the triacylglycerol structure in the case of studied fats was mainly occupied by saturated fatty acids: myristic (14:0) and palmitic (C16:0) acids. These results are in accordance with the literature, as pork fat was reported to contain 80–90% of palmitic acid at the
sn-2 position [
54,
55]. The share of unsaturated oleic and linoleic fatty acids in the
sn-2 position was not high. This proved that unsaturated fatty acids were mainly located in external positions (
sn-1,3) in the triacylglycerol molecules of pork fats. Taking into account the structure of triacylglycerols, it can be stated that there was no significant differences in the distribution of fatty acids between internal (
sn-2) and external (
sn-1,3) positions in groin, jowl, and trimming shoulder fats of pigs fed dry or liquid diets. Such distribution of fatty acids among positions in triacylglycerols is typical of pork fat [
56,
57].
It is worth highlighting that the distribution of fatty acids in the triacylglycerol molecules of fats is very important from a technological and health point of view. It affects the digestion and absorption of fatty acids in the human body. Pancreatic lipase, taking part in fat digestion, is capable of detaching fatty acids located only in the external positions (
sn-1,3) of triacylglycerol molecules, and after this process, monoacylglycerols with a fatty acid in the internal position (
sn-2) are formed. Pork fat contains more saturated fatty acids in the
sn-2 position than vegetable fats, in which this position is occupied mainly by unsaturated fatty acids. In lard, for example, the
sn-2 position is mainly occupied by palmitic acid (C16:0). When saturated fatty acids are located in the
sn-2 position, it has a positive effect on the fat absorption process. Saturated monoacylglycerols and polyunsaturated fatty acids and their salts obtained after hydrolysis have a high absorption rate. A large share of saturated fatty acids in the external positions (
sn-1,3) of triacylglycerols has an adverse effect on fat digestibility. Saturated fatty acids present in these positions, detached from triacylglycerol molecules after the digestion process, tend to form poorly soluble calcium salts, which may result in calcium deficiencies in the body and significant deterioration of fat absorption [
55].
Authors have reported many advantages of applying liquid feeding systems compared to dry feeding. These include improved nutrient utilization, the possibility of using liquid by-products, and improved animal performance [
58,
59,
60]. Additionally, introducing liquid to a diet can help digestion by facilitating the breakdown of nutrients, which can further enhance feed conversion efficiency. Liquid feeding form can also enhance gut health, reduce the need for feed medications and improve animal well-being [
60,
61]. Liquid feeding systems often improve the palatability of the feed, which can lead to increased feed intake. This increase in feed intake can often lead to improved growth rates, as the pigs are consuming more nutrients that are vital for their development. Notably, fat quality is influenced by physical and nutritive characteristics, which are both related to the fatty acid composition of the fat depots. The major issues related to fat quality are fat softness, oxidative rancidity, and the impact of the composition of pork fat on human health. The composition of dietary fat, used in liquid and dry feeding systems in this study (
Table 1), could affect the quality of the fat deposits in pigs. Benz et al. [
61] reported that pigs’ diets supplemented with soybean oil increased the amount of unsaturated fat deposited. Increasing the feeding duration of soybean oil increased C18:2
n-6, PUFA, UFA:SFA ratio, and PUFA:SFA ratio and decreased C18:1
cis-9, C16:0, SFA, and MUFA concentrations in jowl fat and backfat. It should be highlighted that feeding ingredients with relatively high levels of unsaturated fatty acids increase the degree of unsaturation of the fat tissue, consequently decreasing fat firmness, and negatively impacting fat quality.
The empirical results reported herein should be considered in the light of some limitations. The primary limitation to the generalization of these results is the size of the research group. More studies with larger sample sizes should be conducted to reconfirm the findings. The second limitation concerns the lack of previous research studies on the topic, so the possibility of comparing the results with those of other authors was limited. The third limitation is the lack of information about the content of each fatty acid contributed by the type of diet (in mg/100 g), so it is likely that the amounts are different in the liquid and dry formulations which could influence the results presented in the study.
There is still a need for additional studies regarding the impact of the liquid and dry feeding systems on the quality of pork fat, including fatty acid profiles, their distribution between internal and external positions in triacylglycerol molecules, peroxide value, oxidative stability, and nutritional indexes.