Multimodal Phytochemical and Micronutrient Profiling of Onosma onur-koyuncui Sezer Seeds: Antioxidant and Enzyme Activity Inhibitory Potential

This study aimed to provide the first comprehensive seed-based phytochemical and biological investigation of Onosma onur-koyuncui Sezer, a species endemic to Türkiye, by characterizing its chemical composition and evaluating its in vitro antioxidant and enzyme inhibitory potential. A multi-technique approach combining SPME-GC-FID/MS, GC-FID/MS after silylation, ICP-OES, and UHPLC-HRMS/MS was applied to n-hexane and 70% aqueous methanol seed extracts, together with total phenolic and flavonoid determinations, complementary antioxidant assays, and α-amylase inhibition. p-Cymene (15.00%) was the major volatile, octadecatrienoic acid (27.77%) predominated in the fatty acid profile, and calcium (28.50 mg/gdw) was the most abundant mineral. UHPLC-HRMS/MS revealed chlorogenic acid (51.29 mg/gdw) and diosmetin (42.95 mg/gdw) as major constituents of the 70% aqueous methanol extract. This extract showed the highest phenolic and flavonoid contents and notable antioxidant activity, particularly in the DPPH assay (IC50 = 0.043 mg/mL), exceeding that of BHA (IC50 = 0.118 mg/mL), and exhibited α-amylase inhibition (IC50 = 0.40 mg/mL). These findings provide the first integrated characterization of O. onur-koyuncui seeds and highlight their phytochemical diversity and antioxidant potential.