Profiling of Bioactive Metabolites and In Vitro Multifunctional Properties of Postbiotic Cell-Free Supernatant Derived from Probiotic Lactic Acid Bacteria Isolated from Fermented Olives

This work aims to characterize the bioactive metabolite profile and in vitro multifunctional properties of postbiotic cell-free supernatants (Postbiotic-CFSs) derived from three lactic acid bacteria (Levilactobacillus brevis S27, Lactiplantibacillus pentosus S42, and Lactiplantibacillus plantarum S62) isolated from fermented green olives. The postbiotic-CFSs were analyzed for their bioactive metabolites, emulsification index E24%, and antimicrobial, antioxidant, anti-inflammatory, and antidiabetic activities. The bioactive metabolites identified in all postbiotics included organic acids (lactate, citrate, and oxalate), SCFAs (acetate), hydrogen peroxide, diacetyl, exopolysaccharides (EPSs), proteins, biosurfactants, polyphenols, and flavonoids. The postbiotic-CFSs exhibited emulsification index (E24%) values ranging from 21.5% to 38.2%. Furthermore, they demonstrated antimicrobial properties with inhibition diameters ranging from 14.10 to 16.9 mm against pathogenic bacteria and from 15.8 to 23.50 mm against yeast, while fungal mycelial growth was inhibited by 35.77 to 45.09%. All postbiotics demonstrated antioxidant activities of DPPH from 65.91 to 68.55% and FRAP values from 1707.31 to 1765 µg AAE/mL, as well as anti-inflammatory activity (11.83–12.88%) and antidiabetic activity (34.38–93.75%). These findings highlight the significant potential of postbiotic-CFSs as natural bio-preservative agents in food products and as a source of bioactive metabolites with multifunctional health benefits for consumers.