1. Introduction
In the post-antibiotic era, it is important to have a complete understanding of how gut bacteria grow and interact with prebiotics and with animals. Probiotics and prebiotics are among many additives considered for use in pig nutrition that deserve attention. Various types of oligosaccharides, e.g., inulin, are regarded as a source of prebiotics. Inulin is a water-soluble fructose polymer found mainly in chicory roots (
Cichorium intybus) or Jerusalem artichoke tubers (
Helianthus tuberosus). It contains both oligosaccharides and polysaccharides, which are responsible for its prebiotic properties [
1]. Inulin is composed of a glucose molecule linked with a chain of fructose molecules (from a few to several tens) [
2]. It is included among the prebiotics, i.e., substances promoting the growth of bacteria that constitute the normal intestinal flora [
3]. Dietary inulin and FOS are not hydrolyzed by mammalian enzymes, but are readily fermented by the bacterial community in the caecum and colon and favor the growth of intestinal bifidobacteria [
4]. The growth of
Bifidobacteria and
Lactobacillus is the best-known effect of inulin [
5], which exerts a health-enhancing impact through the stimulation of these bacteria [
6,
7]. The microflora produce numerous nutraceutical compounds, e.g., organic acids, hydrogen peroxide, acidolin, acidolphillin, reuterin, lysozyme, lactoferrin, and lactoperoxidase, as well as such bacteriocins such as lactocidin and lactocin, which exhibit immunomodulatory and antibacterial properties [
8,
9]. Through the promotion of the growth of lactic acid bacteria, inulin exerts an indirect beneficial effect on the host immune system through, e.g., the production of anti-inflammatory cytokines, mononuclear cells, and phagocytic macrophages. It is also involved in the induction of the synthesis of immunoglobulins, in particular IgA [
10]. Inulin has a positive effect on the intestinal immune system, blood flow through the mucosa, and the activity of the local nervous system. Additionally, it increases the intestinal absorption of minerals (improved absorption of iron, zinc, magnesium, and calcium ions in in vitro studies). It also modulates insulin and sugar levels, plasma lipids (cholesterol and triglycerides), weight reduction, and, secondarily, the course and development of atherosclerosis and its complications. Pigs are an excellent model with regard to human metabolism. Hence, the obtained results concerning, among other things, the metabolic profile of blood, as well as the composition of fatty acids deposited in the muscles and reserve fat of pigs, may provide an interesting reference as to the effectiveness of the use of probiotics and prebiotics in the human diet.
The aim of this study was to assess the effect of the addition of a probiotic composed of the following bacterial strains: Lactococcus lactis IBB500 min > 109 cfu/g, Carnobacterium divergens S1 min > 109 cfu/g, Lactobacillus casei ŁOCK 0915 min > 109 cfu/g, Lactobacillus plantarum ŁOCK 0862 min > 109 cfu/g, and Sacharomyces cerevisiae ŁOCK 0141 min > 107 cfu/g to diets supplemented with pure inulin (linear β fructans with a degree of polymerization (DP) ≥ 15) or inulin contained in dried Jerusalem artichokes on the production performance, post-mortem carcass quality, technological parameters of meat, and the composition of fatty acids in backfat and the longissimus lumborum muscle.
3. Results
The chosen indices of fattening performance and carcass slaughter analysis are presented in
Table 3. The probiotic and prebiotic supplementation improved the average body weight gains (
p ≤ 0.05); however, in the case of the prebiotic factor, a significant effect was noticed in the group receiving inulin. None of the additives affected the feed conversion ratio. The prebiotic influenced the backfat thickness, which was lower in pigs fed with dried Jerusalem artichoke (
p ≤ 0.05). Neither the prebiotic nor probiotic used in this experiment affected the weight of the analyzed organs (liver and kidneys).
The results of proximate composition, TBARS content, and pH values of the m. longissimus lumborum of fatteners fed with prebiotics and probiotics are presented in
Table 4. In general, the addition of the prebiotics resulted in a higher percentage of intramuscular fat (IMF); however, the significantly highest level was found in the DJA-40 group, in comparison with the I-20 and C-0 groups. In contrast, the addition of the probiotics (Pro+) reduced its content significantly (
p ≤ 0.05) in the longissimus lumborum muscle compared to the fatteners from the Pro− group. The addition of both prebiotics (I-20 and DJA-40) significantly (
p ≤ 0.05) improved (by approximately 16% and 18%) the antioxidant stability of meat, as expressed by the TBARS value. The meat pH was not affected by any feed additives and their interaction. The initial and ultimate meat pH ranged from 6.57 to 6.64 and from 5.69 to 5.72, respectively. However, lower pH
45 values (6.57–6.59) were found in meat from the I-20 and DJA-40 groups in comparison with the C-0 group (6.64).
The addition of I-20 significantly (
p ≤ 0.05) modified all instrumentally measured color parameters (except L*) compared to the C-0 group, but only in fresh meat (
Table 5). The addition of DJA-40 had a similar effect. Fresh meat from both prebiotic groups was brighter, less red, and more yellow and showed a higher hue angle. In contrast, the color of meat from fatteners fed with the probiotics (Pro+) did not differ from that of pigs from the Pro− group. The heat treatment of the meat (denaturation of muscle proteins) eliminated all differences in the color indices between the groups.
The addition of the prebiotics and probiotics had no effect on any of the evaluated sensory attributes, and no interaction was found between these factors (
Table 6). However, scores higher by 0.2 pts were obtained for the palatability of the meat from fatteners receiving both prebiotics (I-20 and DJA-40 vs. C-0) and probiotics (Pro+ vs. Pro−). No significant interaction was found for the assessed texture parameters of cooked meat, except for WB shear force (SF WB) (
Table 6). As for the main effects of the individual factors, only the effect of the prebiotic on shear force and shear energy in the Warner–Bratzler test, as well as hardness, gumminess, and chewiness in the texture profile analysis (TPA) test, were found to be significant (
Table 6). The addition of inulin, irrespective of its source (I-20 or DJA-40), significantly (
p ≤ 0.05) improved all meat texture characteristics (except springiness) compared to the control group (C-0) (
Table 6). The addition of inulin (I-20 and DJA-40) reduced WB shear force by 17% (
p ≤ 0.05) and 6%, and energy force by 27% (
p ≤ 0.05) and 23% (
p ≤ 0.05), respectively. In the TPA test, hardness, gumminess, and chewiness decreased significantly (
p ≤ 0.05) by 39%, 34%, and 35% in the I-20 group and by 35%, 21%, and 21% in the DJA-40 group, compared to the C-0 group. The extent of the improvement was significantly greater for the addition of I-20 than that of DJA-40 with regard to gumminess and chewiness. In contrast, the diet supplemented with the probiotics had no effect on the textural parameters of meat.
More favorable values of the water-holding capacity parameters, including the significantly (
p ≤ 0.05) lower amounts of free water and the higher M/T ratios, were found for the meat samples of fatteners fed with the inulin additive (I-20 and DJA-40) compared to the control group (
Table 7). The addition of the probiotics to the feed did not affect the water-holding capacity of the meat.
The fatty acid composition of meat is presented in
Table 8. The prebiotic supplementation did not influence the fatty acid content in the meat, except C16:1, which was increased by the dried Jerusalem artichoke as well as the PUFA n-6/n-3 ratio, which was decreased by this prebiotic (
p ≤ 0.05). The probiotic additive in feed significantly lowered the C18:2 fatty acid content in the meat (by 7.2%;
p ≤ 0.05), which resulted in an approx. 6% lower PUFA n-6 and PUFA n-6/n-3 ratio. The atherogenicity and thrombogenicity indexes and the h/H ratio were not affected either by the pre- or probiotic supplement (
Table 8).
In the case of the backfat, the dried Jerusalem artichoke decreased the SFA content (
p ≤ 0.05) in comparison to the control group, mostly because it reduced the content of C14:0 fatty acid by about 9% (
Table 9). Both prebiotics lowered the thrombogenicity index and increased the h/H ratio, but a significant difference was observed only between the dried Jerusalem artichoke and the control group (
p ≤ 0.05). There was no significant difference in the fatty acid composition in the backfat between pigs fed with or without the probiotic supplement.
4. Discussion
Genetic factors and rearing conditions, including nutrition, determine the efficiency of pig rearing and the production of high-quality pork [
38]. The content and quality of nutrients, mainly protein and energy, largely determine the nutritional and dietary value of pork [
39]. Feed additives are also noteworthy, as they shape the microbiome of the digestive tract, influence the health of animals, and improve the utilization of nutrients. Due to the significant or complete limitation of the use of antibiotic growth promoters (AGP), phytobiotics, eubiotics, probiotics, and prebiotics are increasingly being used. Previous studies have shown the beneficial effects of oligosaccharides [
40] and probiotic bacteria [
41], as well as synbiotics [
42] in piglets and fatteners. The enrichment of diets with these additives has contributed to the reduction of diarrhea and better weight gain in piglets [
43]. In fatteners, it improved the digestibility and utilization of feed nutrients and the quality of pork [
44].
After 98 days of fattening, the average body weight of fatteners was 114.2 kg. The differences in the individual fattening periods were similar to those for the whole fattening period, so we did not provide values for individual fattening periods. The results of the present study showed higher final weights and better daily gains when the pigs were fed with diets supplemented with both inulin and with dried Jerusalem artichokes; however, a stronger effect was observed in the case of inulin supplementation. This resulted from the better action of chemically pure inulin than inulin contained in the dried Jerusalem artichoke. The additional enrichment of the feed with the probiotic increased this effect and slightly improved feed conversion. Recent studies have highlighted the suitability of inulin in pig nutrition. The most visible is its beneficial effect on growth performance in growing–finishing pigs [
45], mainly via a positive effect on the duodenum and ileum morphology (the ratio of villus height:crypt depth); elevated activity of sucrose, glucose, and metal transporters in the ileum mucosa; decreased pathogen bacteria; and the expression of pro-inflammatory cytokines [
46].
The additives used in the present study also contributed to the differentiation of the fat content in the pig carcasses, as the animals fed with diets supplemented with both forms of the prebiotics had lower backfat thicknesses at all measuring points. It is likely that the oligosaccharides contained in Jerusalem artichokes, as well as in pure inulin, limited the deposition of stored fat via the production of short-chain organic acids in the large intestine. As reported by Birmani et al. [
47], the explanation is that the inulin oligosaccharide can reduce the expression and activity of fat-producing enzymes in the liver, consequently reducing the synthesis of fatty acids and triglycerides.
The measurement of muscle tissue pH allows the identification of quality defects in raw pig meat, most often as PSE or acidic meat. The typical meat pH obtained as a result of post-slaughter glycogenolysis ensures favorable sensory and technological properties, including an attractive color, tenderness, and palatability, as well as a good water-holding capacity [
48]. It is assumed that an ultimate pH (24 and 48 h after slaughter) of case-ready pig meat should have a range of 5.50 to 5.80 [
49]. In the present study, the ultimate pH of the LL muscle ranged from 5.69 to 5.72, indicating correct handling of the animals (good welfare) before slaughter. The risk of meat defects (RSE or PSE) is minimal at an ultimate pH >5.7 [
50]; therefore, a higher ultimate pH should improve meat quality. Despite the observed differences, the TBARS value was at a relatively low level, since odor deviations in pig meat are perceptible sensorially in the range of 0.5 to 1.0 mg MDA/kg meat [
51]. The higher oxidative stability (lower TBARS values) found in the muscles of fatteners receiving the addition of the prebiotics (I-20 and DJA-40) may be related to the lower content of muscle pigments (myoglobin), which show pro-oxidative effects due to the presence of Fe (according to Min et al. 2008) [
52]. This is indicated by higher lightness (higher L* values) and lower redness (lower a* value), which are correlated with heme pigments in the meat of pigs (according to Lindahl et al., 2001) [
53]. Furthermore, it should be noted that the higher antioxidant stability was not associated with the higher IMF content in fatteners fed with the prebiotics (I-20,
p ≤ 0.05; DJA-40,
p > 0.05). The exact cause of these differences is difficult to explain unequivocally, as literature data on the effect of inulin and probiotic administration on the antioxidant status of pork are not known. However, Herosimczyk et al. [
54] showed that pigs fed with a diet supplemented with 1% or 3% native chicory inulin had significantly reduced liver TBARS levels (
p < 0.10) compared to the control group. Hansen et al. (2008) [
55] fed pigs before slaughter with a feed rich in fermentable fiber (10–13.3% dried chicory roots) and reported values similar to those presented in this study for LD muscle parameters such as lightness (L* = 57.09) and drip loss (3.83%) but reported a lower value of ultimate pH (5.61).
The sensory impression is of great importance for the acceptability and quality of meat products. Therefore, meat producers/animal breeders are interested in optimal solutions that can be used to obtain high-quality products. In this context, it is of interest to be able to immediately influence the sensory quality of pork meat through the simple manipulation of feed ingredients, including fructooligosaccharides/inulin [
56]. However, the final decision to use inulin from chicory depends on the feeding period, the sex of the pigs, and the expected and desired sensory properties of the meat [
55]. In the present study, the meat from gilts and barrows receiving prebiotic and probiotic supplementation in their diet was evaluated. Fermentable carbohydrates, such as inulin, are most commonly used in nutrition for boars (uncastrated males) [
57,
58], due to the effective reduction of the skatole concentration in the hindgut and adipose tissue, thus reducing the incidence of boar taint [
21]. Byrne et al. (2008) [
59] showed that raw and dried chicory and inulin did not lead to a new negative taste and odor sensory characteristics in cooked pork. Even the bitter taste notes characteristic of chicory roots did not cause a negative overall impression. In the case of the effect of inulin on the sensory profile of pork, it was found to be unique, expressed in terms such as feedy, umami, and parsnip. Moreover, there is no explanation for this phenomenon in the literature.
The tenderness of the meat after cooking, expressed as the shear force in the WB test, was significantly different between fatteners fed with or without the prebiotics (
Table 6). The significantly (
p ≤ 0.05) highest values of WB SF were found for the meat of fatteners from the control group (C-0) (64 N on average), whereas the lowest values were obtained in the meat of fatteners fed with the I-20 addition (53.35 N on average). Taking into account the different courses of aging of pig meat, Iwańska et al. (2016) [
60] proposed the following classification of meat tenderness according to WB SF (N/cm
2): very tender < 30, tender 30–45 N, tough 60–90 N, and very tough > 90 N. Assuming this division into classes in the present study, the meat from the control group can be classified as tough and that of the experimental groups (I-20, DJA-40, and Pro+) as intermediate (between tender and tough). However, it should be stressed that these levels of tenderness were already obtained 48 h after slaughter and the meat was not subjected to the aging process.
Rosenvold et al. (2001) [
61] investigated the effect of a high inulin supplement (25%) feeding for 4 weeks before slaughter on the slaughter value and meat quality of gilts. This diet resulted in significantly lower drip loss (4.0%,
p < 0.05) and higher WB shear force of the LD muscle (43 N,
p < 0.05) compared to gilts from the control group (5.2% and 38.5 N, respectively). However, ultimate pH, color (CIE L*a*b*), and cooking losses were not affected. The researchers proposed that the reduced tenderness was probably related to reduced muscle glycogen stores, resulting from a feed that contained low levels of digestible carbohydrates and high levels of fermentable carbohydrates. On the contrary, Aluwé et al. (2013) [
62] showed no effect of inulin addition (from dried pulp and dried chicory roots) on LD muscle quality parameters, except for higher drip loss.
Recently, in regard to the fatty acids analyzed out in our research, we have paid attention to the muscle tissues, because of their greater importance in food in comparison to backfat, and due to consumers’ interest in the dietary quality of meat. The present study shows that supplementation of a diet with a prebiotic (inulin) and a probiotic can influence the fatty acid composition and health-promoting indices of pork products. However, the obtained results were far from the values recommended by the WHO. The literature data concerning the influence of the supplementation of diets with inulin and probiotics on the tissue fatty acid composition are ambiguous. In a study conducted by Brestenský et al. (2016) [
63], the addition of a mixture of inulin and horse chestnuts had no effect on the fatty acid profile, including the ratio of PUFAs n-6/n-3, in the longissimus dorsi muscle of pigs. In a study conducted by Chang et al. (2018) [
64], the meat of the probiotic-supplemented group (
Lactobacillus plantarum) showed higher PUFA contents, with significantly higher levels of linolenic and linoleic acid compared to the control group. Similarly to our results, the PUFA n-6/n-3 ratio was also higher than the values recommended for human health. According to results reported by Juárez-Silva et al. (2019)[
65], the addition of inulin into rabbits’ diets increased the content of beneficial fatty acids (CLA and n3-PUFA) and ensured a better health-promoting index, while reducing the atherogenic and thrombogenic indices of the meat. Similarly, Grela et al. (2014) [
66] found that the fatty acid composition and AI, TI, and h/H indexes of the backfat and meat of fatteners fed with a prebiotic-enriched diet (dried inulin-rich dandelion) indicated a reduced risk of developing atherosclerotic disorders. Contrarily, data presented by Mattioli et al. (2017) [
67] showed that dietary supplementation with prebiotic compounds (inactivated
S. cerevisiae yeast) did not enhance the bioactive fatty acid content in rabbit meat.