Phenolic–Flavonoid Rich Extracts of Digitalis ferruginea subsp. schischkinii Exhibit Strong Antioxidant Potential

The genus Digitalis, classified within the family Plantaginaceae, comprises approximately 36 species with a broad biogeographical distribution extending across Europe, the Mediterranean region, and Western Asia (Davis, 1978). Accumulating evidence indicates that several members of this genus exhibit diverse pharmacological activities, with particular emphasis on their antioxidant and antimicrobial potentials, highlighting Digitalis species as biologically relevant sources of bioactive compounds (Benli et al., 2009; Tusevski et al., 2014; Katanić et al., 2017).Aerial parts and leaves were air-dried, powdered, and subjected to ultrasound-assisted extraction using 70% ethanol. Total phenolic content (TPC) and total flavonoid content (TFC) were quantified using the Folin–Ciocalteu and aluminum chloride colorimetric assays, respectively. Antioxidant activity was assessed via ferric reducing antioxidant power (FRAP) and DPPH radical scavenging assays. All experiments were performed in triplicate, and statistical analyses were conducted using repeated measures ANOVA and one-sample t-tests. Extraction yields reached 18.46% for aerial parts and 17.69% for leaves. Leaf extracts exhibited significantly higher phenolic (41.12 mg GAE/g) and flavonoid contents (34.85 mg QE/g) compared to aerial parts (p <0.05). Consistently, leaves demonstrated superior antioxidant performance, reflected by enhanced ferric reducing capacity (305.15 mg TE/g) and lower DPPH IC50 values (0.0747 mg/mL). A strong positive correlation was observed between phenolic–flavonoid content and antioxidant activity, underscoring the contribution of polyphenolic constituents to the bioactivity of the extracts. The findings reveal that D. ferruginea subsp. schischkinii, particularly its leaves, represents a potent source of natural antioxidants. Beyond its established cardiotonic relevance, this species emerges as a promising candidate for further pharmacological and nutraceutical investigations, thereby expanding the functional significance of the genus Digitalis.