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

A new positively charged, submicronized fat emulsion with appropriate stabi lity during the autoclaving process was developed. Only the emulsions prepa red with a combination of ABA block co-polymer (F68) and chitosan were stab le enough to resist the thermic shock induced by autoclaving sterilization. The results indicate that a mixed film consisting of the ABA block co-poly mer and chitosan molecules was formed at the o/w interface with an overall positive surface charge. Conversely, a combination between chitosan with ph ospholipids and/or with a mixture of phospholipids with ABA block co-polyme r 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 3(2) was used to i nvestigate the effect of chitosan and F68 concentrations on the physicochem ical properties of the system and consequently their influence on the stabi lity of emulsions during autoclaving. Both sire and surface charge of emuls ions were significantly affected as a function of the chitosan concentratio n. Formulation with a mean particle size ranging from 125 to 130 nm and wit h a positive surface charge of 20-23 mV was achieved. Moreover, the chitosa n emulsions were autoclaved without a significant change in their particle size. However, increasing the concentration of chitosan needs a higher amou nt 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). (C) 1999 Elsevier Science B.V. All rights reserved.