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Evaluation of phenolic content and antioxidant capacity of different plant parts in three Globularia sp.

The genus Globularia L. belongs to the family Plantaginaceae and includes 22 to 23 species distributed mainly in the Mediterranean area. Some of the species, such as Globularia alypum L., G. trichosantha Fisch. & C. A. Mey. and G. arabica Jaub. & Spach, are used in folk medicine and have known pharmacological activities (hypoglycaemic, cholagogue, laxative etc.). The best explored G. alypum L. is a near threatened species in Croatia and can only be found around Dubrovnik area. The aim of the present study was to examine the content of bioactive phenolics in Globularia sp. that grow wild in Croatia and are more widespread, as well as their potential antioxidant capacity in vitro. Total phenolic, flavonoid and condensed tannin content of different plant parts in G. punctata Lapeyr., G. meridionalis (Podp.) O. Schwarz and G. cordifolia L. were determined spectrophotometrically. Folin-Ciocalteu’s reagent was used for measuring total phenolic content and aluminium chloride for determining flavonoid content. Condensed tannin content was determined by vanillin-H2SO4 assay, while antioxidant capacity of the extracts was evaluated by DPPH and ABTS assays. Total phenolic content ranged from 13.61 to 42.57 mg of gallic acid equivalent (GAE)/g of dry herbal material (DM). The amount of flavonoids varied from 0.84 to 14.47 mg of quercetin equivalent (QE)/g of DM. Antioxidant capacity expressed as mg GAE/g of DM varied from 4.18 to 22.10 in the DPPH assay and from 4.34 to 19.88 in the ABTS assay. Mean values of antioxidant capacity, total phenolic and flavonoid content were highest in G. punctata Lapeyr. Condensed tannin content varied from 0.33 to 9.77 mg of catechin equivalent (CE)/g of DM and was found to be highest in G. cordifolia L. High positive correlation was observed between DPPH/ABTS radical scavenging capacity and total phenolic content (rS = 0.8864, P < 0.001 ; rS = 0.8712, P < 0.001). The results of this study show that the examined species are rich sources of bioactive phenolics in comparison to the related medicinal species G. alypum L. Further investigation of their chemical composition and bioactivity is needed to verify the possibility of their medicinal use.

Globularia L.; phenolics; flavonoids; condensed tannins; antioxidant capacity

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