Modified coconut pulp particles: The potential candidate for stabilizing Pickering emulsions

Abstract

Coconut pulp, a by-product of coconut milk extraction, was used to prepare Pickering emulsion–stabilizing particles by modification with citric acid (CA) through dry heat treatment. The treatment temperature (100, 120, and 140 °C) and CA concentration (0.7, 2.0, and 3.3 % w/v) were varied. Modification at 100 °C and high concentration of CA gave products with satisfactory appearance and surface characteristics. The product obtained by treatment at 3.3 % CA and 100 °C had a yellowish white color with a light and porous surface, 0.08 degree of substitution (DS), 70° water contact angle, −50 mv zeta potential, and an average particle size after homogenization of 8.4 µm. Unmodified CP powders could not stabilize the oil-in-water (O/W) emulsion, and phase separation occurred rapidly at 25 °C, while CP modified using 2.0 % and 3.3 % CA at 100 °C could stabilize the emulsion for at least 30 d. The oil droplet size decreased as the DS of the particles increased from 77.3 to 33.3 µm and 18.6 µm for the particles with DS of 0.046, 0.072, and 0.082, respectively. The higher hydrophobicity imparted by CA modification strongly affected the oil droplet size, while the negative surface charge of particles supported the uniform dispersion of free CP particles in the interspace among the oil droplets.