ENCAPSULATION OF OLIVE LEAF EXTRACT OBTAINED USING NADES: MORPHOLOGICAL, STRUCTURAL, AND THERMAL CHARACTERIZATION

Olive cultivation has expanded in Brazil, particularly in Rio Grande do Sul, contributing to the generation of olive leaves, an underutilized by-product rich in phenolic compounds with antioxidant potential. Conventional extraction methods rely on organic solvents associated with environmental and operational limitations. Ultrasound-assisted extraction (UAE) promotes cell disruption through acoustic cavitation, while natural deep eutectic solvents (NADES) offer an alternative due to their low volatility and tunable properties. Combining UAE and NADES represents an approach for recovering bioactive compounds from olive leaves. Encapsulation may facilitate the incorporation of these compounds into food systems, although its protective effects require direct assessment. This study aimed to characterize the morphological, structural, and thermal properties of particles containing olive leaf extract (OLE) obtained by UAE using NADES. The OLE (Olea europaea L. cv. Coratina) was extracted using choline chloride:citric acid (1:2 molar ratio) containing 20% water, for 45 min at a 1:30 solid-to-solvent ratio. No control extraction using conventional solvents was performed. Encapsulation was carried out by complex coacervation at pH 4.53, determined by turbidimetric analysis, using gelatin and gum tragacanth (1:1, w/w), followed by freezing and freeze-drying. Control particles without extract were prepared under the same conditions. Total phenolic content was determined in the extract. Encapsulation efficiency (EE) was determined by quantifying total phenolic content on the particle surface and within the particles after disruption. Process yield was calculated based on the solids content of the wall materials and the amount of extract used. The particles were characterized by Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). The extract showed a total phenolic content of 949.98 ± 32.25 mg GAE 100 g⁻¹, while EE and process yield were 40.25% and 34.67%, respectively. SEM revealed irregularly shaped particles with a porous and heterogeneous structure, hindering particle size determination. FT-IR spectra were dominated by wall material bands, while characteristic bands of the extract and NADES, including the 1721 cm⁻¹ band (C=O stretching of citric acid), were absent or attenuated. No new bands indicative of covalent bond formation were detected. DSC revealed initial endothermic transitions at 87.9 °C for the extract and 90.5 °C for the NADES, while control and extract-loaded particles showed transitions at ~24 °C. Additional transitions at 130–135 °C and degradation events at 253–254 °C were observed in both formulations. Complex coacervation enabled the incorporation of OLE into a gelatin–gum tragacanth matrix, supporting the feasibility of combining NADES-based extraction and encapsulation to valorize olive leaf phenolics. However, the protective effect of encapsulation was not directly assessed. Further studies on biopolymer–NADES interactions, phenolic retention, storage stability, and release behavior are needed to advance the development of functional food ingredients aligned with the circular economy.