Phytochemical Profiles and Antimicrobial Activity of Alnus glutinosa (L.) Gaertn. Leaves Growing in Kazakhstan

Alnus glutinosa (L.) Gaertn. has extensive use in traditional medicine and diverse biological activities due to its rich phytochemical profile. In this study, firstly, the physicochemical characteristics of the plant material were evaluated, revealing a high content of extractive substances (17.684%), followed by ash (6.740%) and moisture (5.000%). Among the bioactive constituents, tannins were the most abundant (7.439%). Analysis of macroelements in the plant ash showed K (11.4330 mg/g) as the predominant element, followed by Mg (97.13 mg/g), Ca (75.30 mg/g), and Na (72.41 mg/g). Trace element analysis indicated Fe (1.2266 mg/g) as the most abundant microelement, with Zn (0.8870 mg/g) and Mn (0.8141 mg/g) present in comparable amounts. Gas chromatography–mass spectrometry (GC-MS) analysis of the ethanolic leaf extract characterized volatile and semi-volatile constituents of 43 phytochemical components, where vitamin E was the predominant compound (20.52%), followed by phytol (12.46%) and squalene (10.29%). Further high-performance liquid chromatography (HPLC) analysis confirmed the presumed presence of naringin (56.421 mg/L), followed by epicatechin (15.123 mg/L), catechin (12.485 mg/L), and phloridzin (11.800 mg/L), while gallic acid was detected at a comparatively lower concentration (0.402 mg/L). The antimicrobial activity of the aqueous leaf extract was evaluated against typical Gram-positive and Gram-negative pathogens, including Staphylococcus aureus, Salmonella abony, Escherichia coli, and Klebsiella pneumoniae. To evaluate the effect of compositional changes on antimicrobial activity, the fermented and non-fermented formulations of A. glutinosa leaf extracts were prepared. These results demonstrate measurable antibacterial effects, thereby confirming the ethnopharmacological significance of A. glutinosa and highlighting its potential as a source of natural antimicrobial agents for further pharmacological development.