# Metal-Chelating Macroalgal Extract as a Marine Antioxidant for Stabilizing DHA Nanoemulsions

## TL;DR

This study explores using macroalgal extracts as natural antioxidants to stabilize DHA nanoemulsions, showing some effectiveness but finding synthetic chelators more efficient.

## Contribution

The study introduces macroalgal extracts as a natural alternative to synthetic chelators for stabilizing DHA nanoemulsions.

## Key findings

- Macroalgal extract slowed oxidation and reduced volatile oxidation markers in DHA nanoemulsions.
- Extract-treated nanoemulsions showed physical stability with consistent droplet size and zeta potential.
- EDTA provided better oxidation protection than the macroalgal extract under severe prooxidant conditions.

## Abstract

Docosahexaenoic acid (DHA), an omega-3 fatty acid essential for human health, is highly prone to oxidation in nanoemulsions due to their large interfacial area and presence of transition metal ions. This study investigated macroalgal chelators for stabilizing DHA-rich nanoemulsions. Sequential enzymatic–alkaline extraction using Alcalase® produced an extract with the strongest Fe2+-chelating activity (IC50 = 1.22 mg/mL), protein content of 10.11 ± 0.15%, and total phenolics ≈ 17 µg GAE/mL. This extract was incorporated into nanoemulsions (5 wt% DHA oil, 1 wt% Tween® 20) at 0.61, 1.22, and 2.44 mg/mL and compared with controls containing EDTA (0.025 mg/mL) or no antioxidant. Droplet size remained stable (D3,2 ≈ 77–80 nm; D4,3 ≈ 199–215 nm) and zeta potential averaged −17 to −19 mV, confirming physical stability. Confocal microscopy revealed concentration-dependent interfacial adsorption of extract components. During iron-accelerated storage, extract-treated nanoemulsions slowed hydroperoxide formation and delayed tocopherol depletion compared to the control, while reducing volatile oxidation markers such as 1-penten-3-ol by up to 40%. However, EDTA consistently provided superior protection against oxidation. These findings highlight the potential of macroalgal extracts as clean-label, natural chelators for mitigating metal-driven oxidation in DHA nanoemulsions, though synthetic chelators remain more effective under severe prooxidant conditions.