Development And Characterization Of Chitosan Based Pickering Emulsions Prepared By High Pressure Homogenization

Chitosan is the only natural cationic polysaccharide and the second abundant natural biopolymer in nature.It has bactericidal,anti-inflammatory,hypolipidemic,hypoglycemic,anti-cancer and other functional characteristics.Pickering emulsion based on chitosan self-assembly particles has not only the physiological activity of chitosan molecules,but also the embedding and long-term storage of active components.Though chitosan self-assembled micro-nanometer particles regulated by p H is easily obtained,the performance of chitosan Pickering emulsion under high p H is restrained by large agglomerated particles due to poor self-assembly controllability of chitosan molecules under high p H conditions.High pressure homogenization is ideally suitable for preparing chitosan Pickering emulsion with better properties due to the fact that high pressure homogenization can effectively break large agglomerated particles through multiple mechanisms such as high speed impact,high shear,cavitation effect.This dissertation focuses on research of the effects of high pressure homogenization on Pickering emulsion based on chitosan self-assembly particles.High pressure homogenization process was used to directly prepare chitosan self-assembled Pickering emulsion.The emulsion drop size,centrifugal stability and long-term storage stability were used as indicators,and the effects of high pressure homogenization pressure,the number of homogenization cycles,p H,chitosan concentration and oil-water ratio on the performances of chitosan Pickering emulsion prepared by high pressure homogenization were analyzed.After comparing with the performance of chitosan Pickering emulsion prepared by several different methods,high pressure homogenization method was superior to hand shaking method and high shear homogenization method and was similar to ultrasonic homogenization method because high pressure homogenization has great capacity of breaking large chitosan agglomerated particles.Stable chitosan Pickering emulsion could be prepared by high pressure homogenization under the conditions of low homogenization pressure and less numbers of homogenization cycles.The stability of chitosan Pickering emulsion under low or high oil-water ratios was good and the stability of chitosan Pickering emulsion under middle oil-water ratio was poor due to two distinct stable mechanism under different oil-water ratios.The stability of chitosan Pickering emulsion under low oil-water ratio depends on the chitosan particle sizes and the stability of chitosan Pickering emulsion under high oil-water ratio has strong connection with three dimensional network structure made of chitosan emulsion drops,similar to gelatinous structure.Though high stable chitosan Pickering emulsion could be obtained near the isometric point or under higher p H,chitosan Pickering emulsion could not be directly prepared when the p H of chitosan solution exceeds 6.7 because large agglomerated chitosan particles are easy to clog the gaps of high pressure homogenization valves.The emulsification problem resulted from high p H limits the application of high pressure homogenization in preparing chitosan Pickering emulsion.To resolve the above-mentioned emulsification problem caused by high p H,a new Pickering emulsion preparing method combining high pressure homogenization process and the continuous modulation of p H was developed in this dissertation.The process of the new emulsification method mainly includes two important parts.Chitosan Pickering emulsion under low p H is first fabricated,and then high stable chitosan Pickering emulsion under high p H can be obtained though synchronizing high pressure homogenization process with the continuous modulation of p H.The emulsion drop size and long-term storage stability were used as indicators,and the effects of high pressure homogenization pressure,p H,chitosan concentration and oil-water ratio on the performances of chitosan Pickering emulsion prepared by new emulsification method were analyzed.Super stability of chitosan Pickering emulsion prepared by the new method combining high pressure homogenization process and the continuous modulation of p H is mainly attributed to two aspects: one is very small emulsion drop size,the other is three dimensional network structure formed with chitosan emulsion drops.In comparison with the other methods,the new method combing high pressure homogenization process and the continuous modulation of p H can fabricate super stable chitosan Pickering emulsion under the conditions of lower homogenization pressure,smaller oil-water ratio and high p H range.These finding are of great value and significance for expanding the application of chitosan Pickering emulsion in food,medicine,cosmetics and other fields.