**12. Postbiotics and beyond**

As previously detailed, *P. freurenreichii* probiotic effect has been associated to several factors, including cytoplasmic and surface-exposed proteins [52, 77, 82, 83], short chain fatty acids [62, 63], metabolites [71, 72, 75] and culture supernatants [58, 94] (**Figure 4**). These probiotic-derived factors, which exert a beneficial effect on the host, have been referred as postbiotics [102]. "Postbiotic" is an emerging denomination that encompasses probiotic-derived cell-free metabolic products with health-promoting properties, including proteins, lipids, organic acids, vitamins, supernatants, among others [102–104]. The advantages of postbiotics over probiotics include purity, easy production and storage, industrial scalability, higher specificity in the mechanism of action and less adverse effects [102, 103].

In the case of *P. freudenreichii*, a remarkable example of postbiotic is SlpB protein, which was purified and exerted an immunomodulatory effect, i.e. induction of IL-10, in cultured human intestinal epithelial cells [83]. Another example that would fit into postbiotics definition is extracellular vesicles, which are membranous spherical nanostructures that transport molecules between cells [105, 106]. In probiotic bacteria, such as several *Lactobacillus* and *Bifidobacteriaum* strains, extracellular vesicles have been reported as immunomodulatory [107]. In the case of *P. freudenreichii*, we recently described their production by the strain CIRM-BIA129, which has been the first report with physicochemical, proteomic and functional characterization of extracellular vesicles in the species [85]. We identified relevant proteins in their cargo, including SlpB, and demonstrated their anti-inflammatory activity via the modulation of NF-κB pathway in cultured human intestinal epithelial cells [85].

Postbiotics hold promising perspectives for developing novel probioticderived products with enhanced safety and functionality [107]. Moreover, yield and cargo loading optimization are promising for modulating their properties, enhancing their beneficial effect and biotechnological applications [108]. Finally, clinical trials should be conducted in the near future to assure the

suitability of postbiotics and probiotics for therapy and prophylaxis, since they might exert a great impact in human health [93, 107, 109].
