Non-targeted metabolomics and postbiotics survey of an Iranian Koupa cheese Lactiplantibacillus plantarum isolate.

Bacterial postbiotics, bioactive compounds produced by probiotic bacteria, offer enhanced stability and safety compared with live microorganisms, making them valuable candidates for functional foods and therapeutic applications. In the present study, the probiotic properties and postbiotic compounds of a Lactiplantibacillus plantarum strain isolated from a traditional Iranian cheese were investigated. The strain exhibited a 71.28% survival rate under simulated gastrointestinal (SGI) conditions and demonstrated cell surface hydrophobicity and auto-aggregation capabilities of 60.39% and 54.30%, respectively. The cell-free supernatant (CFS) of bacterial culture was extracted with methanol and subsequently fractionated using n-hexane and ethyl acetate. A bioassay-guided fractionation approach was applied to the CFS, involving the identification of the most effective antibacterial extract/fraction against selected microorganisms, the isolation of potent antibacterial fractions via Sephadex LH-20 column, and identification of the active compounds through liquid chromatography-mass spectrometry. EtOAc proved to be the most effective solvent for extracting antibacterial compounds. Fractions 4 and 5 exhibited the highest inhibitory effect against Staphylococcus aureus and Escherichia coli, respectively. Identification of nocardamine and cyclic dipeptides, specifically diketopiperazines such as cyclo(Hyp-Leu) and cyclo(Tyrosyl-Prolyl), as major bioactive constituents in these fractions underscores their notable potential for enhancing health benefits and combating pathogenic bacteria.