Tunicate Cellulose Nanocrystals: A Green Stabilizer for Oil-in-Water Pickering Emulsions

Tunicates are marine organisms with high cellulose content, that can be processed into tunicate-based cellulose nanocrystals (T-CNC). Nanoparticle-based Pickering emulsion (PE) provides superior stability, reduced surfactant usage, and eco-friendly advantages compared to surfactant-based emulsions. This study aimed at studying the effect of T-CNC with a high aspect ratio (90 ± 60) at different concentrations (0.2, 0.3, and 0.4%) and ultrasonication on the stability of 20% oil in water PE at two pH levels (3 and 5). The extracted T-CNC resulted in a particle size of 1294 ± 500 nm, contact angle of 35 ± 5°, and zeta potential values ranging from -22 to -45 mV, indicating pH-dependent surface charge. Ultrasonication combined with high-speed homogenization ensured emulsion stability at 0.2% and 0.3% T-CNC at both pH levels, whereas homogenization alone led to phase separation. Droplet sizes decreased significantly after ultrasonication, from 23-28 μm to 12-16 μm and 25-90 μm to 8-25 μm at pH 3 and 5, respectively. Higher T-CNC concentrations caused a slight droplet size increase at pH 3 and a more pronounced increase at pH 5. Rheological analysis revealed elastic, gel-like textures, with gel strength enhanced at lower pH and T-CNC concentrations. Optical microscopy observation showed minimal changes in droplet morphology at pH 3 after 7 days, while at pH 5, the droplets exhibited significant flocculation and coalescence. The results highlighted the stability of PE against droplet coalescence, driven by strong electrostatic repulsion from the high surface charge and steric hindrance from the elongated particles adsorbed on the oil droplets. This study pointed out that even in small amounts, T-CNC is highly efficient in stabilizing emulsions, presenting a promising solution for applications in the food, pharmaceutical, and cosmetics industries.