Improving physical stability of microalgae protein-based emulsions under acidic and neutral conditions via carboxymethyl chitosan complexation

Abstract

The emulsification stability of microalgae protein (MP) is limited to strongly alkaline conditions, restricting its applications in food processing. This study aims to investigate the capability of carboxymethyl chitosan (CMCS) to improve MP's emulsification stability over a wider pH range. Results indicated soluble MP-CMCS complexes formed at pH 2, 4, and 7, while aggregation of the complexes occurred at pH 8. The complexes stabilized emulsions exhibited smaller droplet sizes and higher absolute zeta potential at pH 2, 4, and 7 compared to pH 8. After 2 weeks of storage, emulsions remained stable at pH 2, 4, and 7, with significant delamination at pH 8. Laser confocal microscopy confirmed uniform droplet distribution at pH 2 and 7, with slight fusion at pH 4. The complexes stabilized emulsions exhibited higher viscosity and shear stress than MP stabilized emulsions at pH 2, 4, and 7. The stronger viscoelastic properties and higher storage moduli (G') values of MP-CMCS complexes under acidic and neutral conditions indicated stronger intermolecular interactions compared to alkaline conditions. The increase in G' and loss moduli (G") values for emulsions at pH 8 under stress highlighted the significant impact on network structure strength and viscosity in these emulsions. This study elucidated the binding interactions between MP and CMCS under various pH conditions, and demonstrated a feasible approach to improving MP's emulsification stability over a wider pH range.