Structural characterization and bioaccessibility of nanoliposomal lutein from pumpkin extract

Pumpkin processing by-products represent a sustainable source of lutein; however, the poor stability and low gastrointestinal bioaccessibility of free lutein limit its practical application in functional foods. Previous studies have largely focused on either extraction optimization or encapsulation separately, lacking an integrated approach that combines green extraction with nanoencapsulation to address both recovery and delivery challenges. The objective of this study was to recover a lutein-rich carotenoid extract from pumpkin peel using supercritical CO₂ and subsequently encapsulate it into food-grade nanoliposomes (NLPs) at varying lutein/lecithin ratios (0.5%, 0.75%, 1.0%, and 1.5% w/w). The physicochemical properties, structural characteristics, antioxidant activity, in vitro release, and gastrointestinal bioaccessibility of the resulting formulations were systematically evaluated. Lutein-loaded NLPs exhibited mean particle sizes ranging from 109 to 272 nm with negative zeta potentials (- 22.1 to - 29.1 mV), indicating good colloidal stability. Encapsulation efficiency increased with lutein/lecithin ratio, reaching a maximum of 86.3% at 1.0% loading (NLP3). SEM confirmed spherical nano-vesicles, while FTIR, DSC, and XRD analyses demonstrated successful incorporation of lutein into the lipid bilayer and its transformation from a crystalline to an amorphous state. Under simulated gastrointestinal conditions, NLP3 showed the highest lutein release (≈ 73.0%) and micellar bioaccessibility (45.2%), representing approximately a two-fold enhancement compared with lower-loading formulations. Storage studies revealed superior lutein retention in NLP3 (≈ 85%, 78%, and 75% after 1, 15, and 30 days, respectively). Moreover, DPPH assays indicated that nanoliposomal encapsulation effectively preserved lutein antioxidant activity during storage and enabled sustained radical scavenging behavior. Overall, this work demonstrates an integrated valorization strategy combining green extraction and nanoliposomal delivery to enhance the stability, release, and bioaccessibility of lutein from pumpkin agro-industrial waste, highlighting the potential for developing sustainable, value-added functional food ingredients, nutraceuticals, and food fortification systems.