Physicochemical properties of chitosan-lipid emulsions and their stability during the autoclaving process

A new positively charged, submicronized fat emulsion with appropriate stability during the autoclaving process was developed. Only the emulsions prepared with a combination of ABA block co-polymer (F68) and chitosan were stable enough to resist the thermic shock induced by autoclaving sterilization. The results indicate that a mixed film consisting of the ABA block co-polymer and chitosan molecules was formed at the o/w interface with an overall positive surface charge. Conversely, a combination between chitosan with phospholipids and/or with a mixture of phospholipids with ABA block co-polymer showed a phase separation during autoclaving. A chitosan type with a low viscosity was used which was intended for a possible use in the ocular and parenteral application. An experimental factorial design 32 was used to investigate the effect of chitosan and F68 concentrations on the physicochemical properties of the system and consequently their influence on the stability of emulsions during autoclaving. Both size and surface charge of emulsions were significantly affected as a function of the chitosan concentration. Formulation with a mean particle size ranging from 125 to 130 nm and with a positive surface charge of 20-23 mV was achieved. Moreover, the chitosan emulsions were autoclaved without a significant change in their particle size. However, increasing the concentration of chitosan needs a higher amount of F68 in order to achieve stable emulsions during autoclaving. This may be due to the interaction between the positively-charged chitosan and the negatively-charged free fatty acids, which are contained in the oil phase (castor oil).