Unveiling the Chemical Composition and Bioactivity of Nepeta rtanjensis Subcritical Water Extract: A Potential Candidate for Pharmaceutical and Food Preservation Applications.

Nepeta rtanjensis, a local endemic plant from Serbia, was processed using subcritical water extraction, and the resulting extract was further analyzed by high-performance liquid chromatography-diode array detection and gas chromatography-mass spectrometry. Its biological activity, including antioxidant, anti-inflammatory, antihyperglycemic, and antimicrobial effects, was evaluated in vitro. Rosmarinic acid (201.14 mg/100 g extract), along with the monosaccharides glucose (16.15%) and fructose (10.41%), were the predominant metabolites. The extract exhibited significant antioxidant activities in 2,2-diphenyl-1-picrylhydrazyl (33.99 µmol TEAC/100 g extract), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (62.66 µmol TEAC/100 g extract), and ferric ion reducing antioxidant power (311.55 µmol TEAC/100 g extract) tests. Moderate anti-inflammatory (half-maximal inhibitory concentration [IC50] = 80.72 µg/mL) and antihyperglycemic (IC50 = 120.29 µg/mL) effects were observed, although both were less potent than the respective standards. The extract showed strong activity, with inhibition zones of 25.00 mm against Staphylococcus aureus and 18.00 mm against Candida albicans. These results indicate that N. rtanjensis subcritical water extract is a promising candidate for use in antimicrobial formulations, particularly for topical applications or combating skin infections caused by resistant Gram-positive bacteria, and highlight its potential in pharmaceutical and food preservation applications.