## 4 Discussion
Based on these considerations, the FAAs analysis allowed us to reduce the number of selected probiotics from 12 to 4 strains. In fecal media obtained using CKD feces, only _B. animalis_ BLC1, _L. delbrueckii_ SP5, _Lc. casei_ LC4P1, and _Lp. plantarum_ LPAL showed lower proteolytic activity. This result confirmed the evidence of the high protease/peptidase activity of lactic acid bacteria. The proteolytic activity of lactic acid bacteria plays a role in cheese ripening [47] and, through hydrolysis of gliadins and related epitopes, in ameliorating the symptomatology related to gluten malabsorption and celiac disease [48; 49]. Therefore, the last step in the adopted workflow was the characterization of the ability of the four selected probiotics to produce SCFA, given the evidence discussed above [17; 20; 21]. The largest spectrum of SCFAs was achieved using _B. animalis_ BLC1 and _Lc. casei_ LC4P1. Thus, a first innovative symbiotic was developed (NatuREN P), which comprised _B. animalis_ BLC1, _Lc. casei_ LC4P1, FOS, inulin, and pomergnate seed extract. The stability tests showed that, unfortunately, a critical decrease in the probiotics' viability occurred after two months of storage. For this reason, based on the promising results obtained upon administration of polyphenols-enriched tomato and red grape skin extracts in colitis mouse models [27; 34], we then evaluated a polyphenic mixture, named Polimix, including quercetin, resveratrol, and proanthocyanidins. Polimix simulates the polyphenol profile classes of transgenic tomato varieties and red grape skin. Thus, a second innovative symbiotic was developed and named NatuREN G, which comprised _B. animalis_ BLC1, _Lc. casei_ LC4P1, FOS, inulin, quercetin, resveratrol, proanthocyanidins from grapeseed (_Vitis vinifera_ L) powder extract, maltodext from corn, and sodium cyclamate. The stability tests performed on NatuREN G showed that the probioticic cell density remained approximatively stable for two months of product storage, at both room and refrigerated temperatures. Additionally, only a slight decrease in cell density was found after six months of storage. Hence, the development of the present symbiotic occurred within an ongoing research project in which different treatments were being administered to CKD patients. The common aim of previous works was to evaluate whether different dietary interventions with probiotics and prebiotics might ameliorate pathogenomic features in nephropathy. The literature in this field reports conflicting results, where not all treatments reached the expected outcomes. In line with this, [PERSON] et al. found that the administration of _Bifidobacterium longum_ was effective in decreasing indoxyl sulfate (IS) in hemodialyzed patients [22]. The collected data showed that five weeks of treatment were sufficient to decrease serum levels of IS. Similarly, a mixture of different probiotics, including _Streptococcus_, _Lactobacillus_, and _Bifidobacterium_ strains, was administered to hemodialyzed patients [23], even if, in this work, no changes in TMAO levels were found in plasma. Concerning prebiotics, four weeks of treatment with resistant starch showed significant decreases in both the IS and IL-6 plasma levels of hemodialyzed patients [50], while oligofructose-enriched inulin showed its impact by decreasing \(p\)CS levels [51]. Other trials focused on the effects of FOS administration to CKD patients. In one of these studies, FOS produced a reduction in circulating \(p\)CS, even if no changes in IS levels were recorded [52]. Conversely, another study using FOS reported an amelioration in inflammatory parameters and endothelial integrity, whereas only slight but not significant differences in \(p\)CS were found [53]. Before industrial scale-up, NatuREN G was tested in fecal batches prepared from HC and CKD subjects, showing promising results, although confirmation in vivo remains necessary. In detail, a significant increase in both lactic acid bacteria and lactobacilli was found in CKD fecal batches.