Nutritional Composition, Essential Oil Profiling, and Post-Digestion Phytochemical and Antioxidant Properties of Fennel Pignut (Bunium ferulaceum) Seeds

Fennel pignut (Bunium ferulaceum) seeds are used in different foods as food ingredients, contributing to the flavor and aroma of various culinary preparations, yet they remain underexplored as a source of nutritional and bioactive compounds. This study aims to comprehensively characterize the nutritional and phytochemical matrix of B. ferulaceum seeds across their macronutrient, mineral, and phenolic fractions and track the phenolic compounds’ contents and shifts in a multi-assay antioxidant capacity across simulated oral, gastric, and intestinal digestion. The results revealed a carbohydrate-dominant seed (39%), with uronic acid, glucose, and mannose as the principal constituents, and a lipid fraction (4%) characterized by oleic/petroselinic acids (54%). Proteins (19%) provided a nutritionally complete amino acid profile, with arginine as the predominant residue. Phytochemical analysis identified β-caryophyllene and germacrene-B in the essential oil fraction, while the polar extract was rich in hydroxycinnamic derivatives (caffeoylquinic and di-caffeoylquinic acids) and quercetin glycosides. Undigested seed extract contained a total polyphenol content (TPC) of 75.08 ± 1.91 µg gallic acid equivalent (GAE)/mg extract with a good 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical-scavenging ability of 340 μg TE/mg extract. Simulated digestion reduced polyphenol content by 10% during intestinal phase, while antioxidant activity dropped by 82% [2,2-diphenyl-1-picrylhydrazyl (DPPH) radical] and by 46% for oxygen radical absorbance capacity (ORAC) during the same phase compared to the undigested sample. Organic acids and caffeoylquinic derivatives remained detectable during in vitro simulated digestion compared to flavonoid glycosides such as quercetin derivatives, which were undetectable after intestinal digestion. Fennel pignut seeds represent a nutritionally dense and phytochemically rich ingredient. The seeds retained substantial antioxidant activity following vitro digestion, supporting their incorporation into functional food formulations.