Bio-Based Nanoemulsions for the Delivery of Algal Lipids: Stability and In Vitro Gastrointestinal Digestibility Assessment

Algal lipids, particularly those rich in omega-3 fatty acids, are promising functional ingredients due to their health benefits and sustainable profile. However, incorporating them into food systems is challenging. In this study, lipid-based nanoemulsions (NEs) were developed to entrap a food-grade algal lipid extract (LE) obtained via ultrasound-assisted extraction with ethyl acetate from an algae blend (Algaessence®).

NEs were formulated using medium-chain triglyceride (MCT) oil and rhamnolipids (0.05 wt%) as a biosurfactant at two lipid-phase concentrations (1 and 5 wt%). Emulsification was performed through pre-homogenization followed by ultrasonication. Control NEs, without LE, were prepared for comparison. Physicochemical properties (droplet size, polydispersity index (PDI), and zeta potential) were assessed, as well as pH stability (pH 2.5–9.0) and storage stability over 1 month at room temperature (RT) and 4°C. The in vitro digestibility of alpha-linolenic acid (18:3 n-3) was evaluated using the INFOGEST protocol.

At day 0, LE–NEs exhibited small droplet sizes (<200 nm), low PDI (≈0.200), and highly negative zeta potential values (<–65 mV), indicating good colloidal stability. LE–NEs showed smaller droplet sizes than controls, suggesting interactions between LE and the NE interface. After 1-month storage at RT and 4ºC, droplet size increased and zeta potential decreased, while PDI remained stable. However, visual signs of destabilization were more pronounced in NEs stored at RT. LE–NEs also showed improved resistance to pH-induced destabilization. In vitro digestion revealed that NE5% promoted higher C18:3 n-3 hydrolysis (77.2±1.1%) than NE1% (73.2±1.5%) and the non-emulsified LE mixed with MCT oil (62.4±5.0%).

These results demonstrate the potential of NEs as effective carriers for algal lipid delivery. Future studies should explore the NEs' performance in real food matrices.