Evaluating Secondary Metabolites and Antioxidant Activity of in vitro Callus and Micro-Plant Extracts of Hyssopus officinalis L.

Hyssopus officinalis L. is a valuable medicinal plant. Its extracts have good commercial prospects as biologically active substances. Biotechnological production methods that yield valuable secondary metabolites often involve callus cultures, which differ in qualitative and quantitative content of target substances. This research compared phenolic secondary metabolites, antioxidants, and antimicrobial activities in extracts of three callus cultures in vitro, native plants, micro-plants and a commercial preparation of H. officinalis. The extracts were obtained using 70% ethanol. The content of phenolic compounds, flavonoids, hydroxycinnamic acids, and tannins was determined by standard methods. The method of high-performance liquid chromatography revealed the content of individual phenolic compounds. The antioxidant activity tests relied on DPPH, FRAP, and ABTS. The antimicrobial and fungicidal activity was assessed by the disc-diffusion method. The Murashige-Skoog medium with 0.2 mg/L 6-benzylaminopurine and 1 mg/L 2,4-dichlorophenoxyacetic acid demonstrated a high growth index of callus crude biomass (11.6 ± 1.4). The same culture was rich in phenolic compounds (35.5 ± 1.2 mg-eq. gallic acid/g solids), hydroxycinnamic acids (82.5 ± 2.6 mg-eq. rosmarinic acid/g solids), tannins (49.6 ± 0.8 mg-eq. gallic acid/g solids), rosmarinic acid (20.25 ± 1.84 mg/g solids), and caffeic acid (1.48 ± 0.08 mg/g solids). Its extracts showed significant antioxidant activity according to DPPH (127.8 ± 5.6 mg-eq. ascorbic acid/g solids) and FRAP (15.9 ± 1.3 mg-eq. ascorbic acid/g solids). However, they had a rather weak antibacterial and fungicidal activity against Bacillus subtilis (7.2 ± 0.2 mm) and Candida albicans (7.0 ± 0.2 mm) at a concentration of 2 mg/disk. The antibacterial and fungicidal activity against Escherichia coli was equally weak at 1 mg/disk (7.0 ± 0.3 mm) and 2 mg/disk (7.3 ± 0.1 mm), respectively. The extracts of H. officinalis callus cultures and micro-plants in vitro produced the best yield of secondary metabolites compared to the native plant extract. Biotechnological methods proved effective in obtaining valuable compounds from cell cultures.