Ulvan Microparticles for Encapsulation of Eucalyptus Essential Oil: Characterization, Release Behavior, and Stability in Aquafeeds

Abstract

Ulvan–lecithin microstructures were developed as a delivery platform for eucalyptus essential oil (EEO) in functional aquafeeds to improve phytobiotic retention, modulate gastrointestinal release, and enhance pellet stability during storage. Preliminary formulation screening compared ulvan-only and ulvan–lecithin systems containing different lecithin levels. Among the tested formulations, ulvan–1%–lecithin–EEO (U–L1–EEO) showed the most favorable overall profile, with the highest encapsulation efficiency (EE%, 76.4% ± 1.2%), the lowest surface-associated EEO fraction (23.6% ± 1.2%), a median particle size of 145.2 ± 4.8 μm, a narrow size distribution (span = 1.33 ± 0.04), and a negative ζ-potential (−31.6 ± 1.8 mV). Fourier-transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC) analyses supported the formation of a physically stabilized ulvan–lecithin matrix and the incorporation of EEO through mainly noncovalent interactions. In PBS (pH 7.4), U–L1–EEO exhibited sustained release, reaching ~90% after 24 h, with Higuchi and Korsmeyer–Peppas modeling indicating diffusion-governed and anomalous transport behavior during the initial release phase. Under simulated Dicentrarchus labrax gastrointestinal conditions, release was limited during the gastric phase (~12.7% at 90 min, pH 2.5) and increased markedly under intestinal conditions (~82% at 360 min, pH 7.5 with pancreatin and bile salts), indicating preferential intestinal release under the applied in vitro conditions. When incorporated into commercial aquafeed pellets at equivalent EEO inclusion (0.1% w/w), the encapsulated formulation improved accelerated storage stability (45°C, 70% RH, 28 days), reducing moisture uptake and peroxide value (PV) development while improving lipid and ω−3 retention, antioxidant capacity, total phenolic content (TPC), pellet durability, hardness, fines resistance, and water stability. Ulvan–lecithin microencapsulation appears to be a promising proof-of-concept strategy for stabilizing volatile phytobiotics and improving the storage performance of functional aquafeeds, although in vivo validation and process-scale assessment are required before biological efficacy and industrial applicability can be confirmed.