Antioxidant, Structural and Technofunctional Profiling of Seed-Free Sea Buckthorn Pomace Dry Fractionated by Grinding–Sieving

Abstract

Sea buckthorn pomace, generated as a by-product of juice processing, has potential for valorisation as a functional food ingredient. This study investigated whether dry fractionation by grinding and controlled sieving of seed-free sea buckthorn pomace (SBP) can generate granulometric fractions with distinct compositional, antioxidant, structural, and technofunctional characteristics. SBP was separated into six fractions (SBPF1: >2.0 mm; SBPF2: 1.0–2.0 mm; SBPF3: 0.5–1.0 mm; SBPF4: 0.25–0.5 mm; SBPF5: 0.15–0.25 mm; SBPF6: <0.15 mm) and evaluated for proximate composition, colour, water swelling capacity (WSC), water retention capacity (WRC), water solubility index (WSI), oil retention capacity (ORC), total phenolic content (TPC), total flavonoid content (TFC), DPPH radical-scavenging activity, ferric reducing antioxidant power (FRAP), and structural characteristics. Granulometric fractionation resulted in significant differences among the fractions. SBPF1 showed the highest total dietary fibre content (58.46%), with insoluble dietary fibre predominating in the coarser fractions, whereas soluble dietary fibre increased towards the finer fractions. WSC was highest in SBPF3, WRC in SBPF5, WSI increased progressively towards SBPF6, and ORC was higher in the coarser fractions. SBPF4 showed the highest TPC (2984.02 mg GAE/100 g d.w.), TFC (1365.14 mg QE/100 g d.w.), DPPH (315.74 μmol TE/g d.w.), and FRAP (277.63 μmol Fe2+/g d.w.) values. Pearson analysis showed strong positive correlations among TPC, TFC, DPPH, and FRAP, while principal component and agglomerative hierarchical analyses differentiated the granulometric fractions according to their multivariate profiles. Attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy showed preservation of the main absorption regions together with fraction-specific differences in spectral parameters and peak-area ratios, whereas wide-angle X-ray scattering (WAXS) profiles remained broadly comparable, with a diffuse feature around a scattering angle (2θ) of 20° and no newly appearing sharp reflections, although crystallite size differed among fractions and increased from SBPF3 to SBPF6. These results demonstrate that granulometric fractionation can generate SBP fractions with distinct characteristics, supporting their consideration as potential value-added ingredients for further evaluation in specific food applications.