STABILIZATION BY CHITOSAN OF SOYBEAN OIL-EMULSIONS COATED WITH PHOSPHOLIPID AND GLYCOCHOLIC ACID

The interaction between chitosan, a cationic polyelectrolyte having a pK(a) of about 6.2, and emulsified lipids has been measured as a function of pH by electrophoretic mobility. The strongest adsorption of chitosan has been observed on emulsion droplet surfaces stabilized with sodium glycocholic acid (bile salt) mixed with phosphatidyl choline at a pH of about 5. The forces acting between layers of chitosan adsorbed on negatively charged solid surfaces (mica) were measured as a function of pH. From these measurements it is clear that, at low pH, the adsorption of cationic chitosan on to the negatively charged mineral surface results in a charge reversal. When the pH is increased (without changing the adsorbed amount), the charge passes through zero, and, at higher pH values, a negative charge develops. The range of the steric force was used to describe the structure of the adsorbed chitosan layer at different pH values. The flocculation behaviour of an emulsion stabilized by phospholipid and bile salt emulsifiers and adsorbed chitosan has been rationalized by considering the forces acting between negatively charged solid surfaces coated with a chitosan layer.