Phytochemical profile, antioxidant capacity, and enzyme inhibitory properties of Alkanna tubulosa extract obtained via ultrasound-assisted extraction

Abstract

Phytochemicals from under-explored Mediterranean taxa represent an untapped reservoir of multitarget agents for oxidative and metabolic stress management. Here, we characterised the antioxidant and enzyme-modulating potential of a methanolic ultrasound-assisted extract (UAE) prepared from the aerial parts of Alkanna tubulosa. Total phenolics reached 97.34 mg GAEs (gallic acid equivalents)/g and flavonoids 45.03 mg REs (Rutin equivalents)/g. LC-ESI-MS/MS (Liquid Chromatography-Electrospray Ionization-Tandem Mass Spectrometry) identified 17 metabolites, predominantly hesperidin (13626 µg/g) and rosmarinic acid (6637 µg/g). The extract exhibited potent radical-scavenging capacity-DPPH (2,2-Diphenyl-1-picrylhydrazyl): 181.43 mg TEs (Trolox equivalents)/g; ABTS [2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)]: 182.85 mg TEs/g-and high electron-donor power—phosphomolybdenum: 570.77 mg TEs/g; CUPRAC (Cupric Ion Reducing Antioxidant Capacity): 479.07 mg TE/g; FRAP (Ferric Reducing Antioxidant Power): 270.59 mg TE/g-but only moderate Fe²⁺ chelation (6.63 mg EDTAEs (Ethylenediaminetetraacetic Acid equivalents)/g). Enzymatic assays revealed selective inhibition of carbohydrate-hydrolysing enzymes, with α-glucosidase and α-amylase activities equivalent to 598.36 and 299.50 mg ACEs (Acarbose equivalents)/g, respectively; tyrosinase suppression reached 57.30 mg KAEs (Kojic acid equivalents)/g, whereas cholinesterase inhibition was low [AChE (acetylcholinesterase) 2.07 mg GALAEs (Galanthamine equivalents)/g; BChE (butyrylcholinesterase) 1.05 mg GALAEs/g]. These findings position A. tubulosa as a rich source of phenolic acid and flavanone-glycoside-centred antioxidants with promising anti-hyperglycaemic and ancillary dermatoprotective properties. Future work should isolate dominant constituents, evaluate their synergistic interactions and validate efficacy in relevant cellular and in vivo models.

Keywords

• Alkanna tubulosa
• Ultrasound-assisted extraction
• Phenolic compounds
• Antioxidant activity
• Enzyme inhibition

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