**4. Discussion**

There is a grea<sup>t</sup> variety in macrominerals and trace elements content of rabbit meat among different studies. Whereas the potassium content framed within those reported in the literature [1,2,10], phosphorus, sodium and manganese level were below, and calcium was over the range presented by formerly mentioned authors. Moreover, Hermida et al. [10] presented higher iron and manganese, and lower zinc and copper concentrations in rabbit meat, compared with our findings.

The lowest level of calcium in EG1 was similar to the values presented by Dalle Zotte [1]. On the other hand, Nistor et al. [13] reported higher calcium content of rabbit meat (21.4 mg/100 g). Opposite to calcium, the phosphorus level in EG1 (259.50 mg/100 g) was the highest. The indigestible carbohydrates compounds like oligofructose, galactooligosaccharides, and inulin have been found to cause improved mineral retention/absorption by the host organism because of their ability to bind and sequester the minerals, and these carbohydrate-mineral complexes pass unabsorbed through the small intestine onto the colon when the minerals are released from the complex and absorbed. The application of probiotics acts on the nondigestible carbohydrates, causing the short chain fatty acids (SC-FAs) rise which can affect an increased absorption of minerals like magnesium and calcium. Moreover, the probiotic enhanced SCFAs can stimulate Vitamin D receptor expression on the eukaryotic cells, which regulate the absorption of calcium from diet, and its metabolism in mammals [25]. The probiotics can also increase the calcium transporters like TRPV6 and calcireticulin Sp100 in the intestine [26]. Phosphorus is needed for the growth of muscle tissue for being involved in the energy metabolism. Its content was higher compared to our previous experiment with autochthonous *E. faecium* CCM7420 rabbit-derived strain [14] as well as to data reported by the other authors [1,2,10] but still lower than it was reported by Nistor et al. [13]. Wang et al. [27] also demonstrated improved phosphorus absorption and utilization in broilers after *E. faecium* CGMCC 2516 microcapsules' application. Rabbit meat contains more potassium than other types of meat and is recommended for hypertension diet. Although the potassium concentrations decreased in both experimental groups compared to CG, the data were comparable to values reported by Dalle Zotte and Szendr˝o [2].

Increased iron content was noted similarly to our previous results achieved during beneficial E. faecium CCM7420 strain application [14]. Other authors presented higher iron values in rabbit meat: 1.1–1.3 mg/100 g [1] and 0.66–0.99 mg/100 g [11]. It is well known that iron is better absorbed in solution in an acidic environment. In the intestine, the pancreas pours a very alkaline fluid into the upper small intestine and makes the whole contents alkaline; this creates a problem for mineral and trace elements, e.g., iron, zinc absorption. In this case, probiotics could improve the intestinal microbial balance due to lactic acid bacteria, create a beneficial acidic environment in the gastrointestinal tract, and increase the minerals' absorption and their subsequent transferring/inclusion into the meat. The acidic environment can enhance the ionization of minerals that in turn results in passive diffusion [28]. Some studies have been considered showing better iron, copper, and zinc absorption due to improvement of the microbial balance by dietary inclusion of microorganisms—yeasts—in several animals [29–31]. We also hypothesized enhanced enzymatic activity due to improved intestinal microbiota during CCM8558 strain and its EntM application. Another possible way of better mineral absorption could be the enlargement of the absorption surface by proliferation of enterocytes. This fact is also confirmed by improved morphometry parameters, recorded during our previous experiments when beneficial *E. faecium* CCM7420 strain and the EntM were applied to rabbits [32,33]. Copper is an essential trace mineral which performs important biochemical functions, which is usually deficient in the typical human diet. Regarding the copper content, the results vary widely [10,11,34]; our findings agree with those reported by Hermida et al. (0.03–0.21 mg/100 g; [10]). Despite the reduced (but still in the range characteristic for rabbit meat) copper level in both experimental groups compared with

control data, the dietetic value of rabbit meat was not negatively influenced during the beneficial CCM8558 strain and its EntM application.

The majority of reports present higher pH24 (24 h postmortem) values than 5.70. Lower pH48 (48 h postmortem) values (in the range 5.37–5.65) obtained in this experiment could be explained by the depletion of glycogen reserve in muscles during refrigeration and by longer storage time. Similar pH48 values were detected also during the beneficial *E. faecium* CCM7420 strain (5.34–5.65) and phyto-additives' (5.61–5.71) application in rabbits [14,35]. Lower values of lipids were determined, but the protein content of rabbit meat was not influenced using the CCM8558 strain and its EntM. Redness is influenced with the degree of iron oxidation in the heme pigment in myoglobin. At high pH levels, oxymyoglobin is rapidly turned into dark red color reduced myoglobin, showing a positive relationship between these parameters [36]; our findings also confirm this relationship. Higher values of yellowness could be related to free radicals, produced by lipid oxidation during storage and/or manipulation, which can oxidize heme pigments, causing discoloration of meat and meat products [37]. Lower lipid value than the average [1] was determined by us, similarly to Lauková et al. [38] after gallidermin application in rabbits, but contradictory to results achieved during probiotic BioPlus 2B® preparation or phyto-additives' supplementation in rabbits [35,39]. Positive correlation between lipids and energy was found in rabbits of EG1 group, mainly at day 42 (after probiotic strain cessation). The protein content of rabbit meat was not influenced using CCM8558 strain and its EntM, similarly, to results noted through gallidermin administration in rabbits [38]. Improved energy values were previously described also during phyto-additives' application in rabbits [35].
