Preparation And Application Of Deamidated Zein Nanoparticles

As an amphiphilic biomacromolecule,zein can self-assemble to nanoparticles(ZNP).ZNP can not only be used as an emulsifier for Pickering emulsion,but also as a carrier to improve the stability and bioavailability of hydrophobic active substances.Therefore,ZNP has attracted great attention from researchers in the fields of food,cosmetics and medicine.However,due to the high surface hydrophobicity of ZNP,its emulsifying property is poor.In addition,the redispersibility of ZNP becomes worse after drying.This paper mainly focuses on improving the surface hydrophilicity of ZNP.Then,the influence of ZNP as carrier on the physicochemical properties of thymol was deeply explored.Finally,the emulsifying performance of ZNP was discussed.The main results are as follows:(1)ZNP were prepared by antisolvent precipitation method with acid/alkaline pretreated zein.It is worth noting that acid/alkaline treatment of zein molecules can tune the particle size and surface property of the as-prepared ZNP.Compared with acidic conditions,zein molecules pretreated under alkaline conditions have higher deamidation degree and better hydrophilicity,so ZNP with smaller particle size and higher surface hydrophilicity can be prepared.More importantly,ZNP prepared with zein pretreated under alkaline condition had better colloidal stability and re-dispersibility(after freeze-drying).(2)Zein pretreated at pH 7.3 was used as carrier and thymol was used as the active substance,that the antibacterial zein nanoparticles(ZTNP)were prepared by antisolvent precipitation.As the amount of thymol increased,the particle size of ZTNP gradually increased,but the zeta potential of the particles was not affected.The encapsulation effiency(64.98%)was the highest when the ratio of zein to thymol was 5: 3,and the re-dispersibility of nanoparticles was still maintained under this condition.Importantly,the deamidated zein was mainly combined with thymol by hydrophobic interaction and hydrogen bonding force.Thymol exhibited an amorphous state in granules,and the ZTNP significantly improved the water solubility of thymol(~20%).It is worth mentioning that the antibacterial properties of thymol against Escherichia coli(E.coli)and Staphylococcus aureus(S.aureus)were enhanced by ZTNP.(3)The Pickering emulsion was prepared by using ZNP as particle stabilizers.The influence of surface properties of ZNP on the formation and stability of Pickering emulsion was first studied.The results showed that the nanoparticle pretreated under pH=7.3,which is ZNP-7.3,had better emulsification performance,this is mainly because ZNP-7.3 has more suitable wettability at oil-water interface.The results showed that ZNP-7.3 had good emulsification performance in a wide range of pH.As the the particle concentration increased or ionic strength decreased,the emulsion became more stable.In addition,the oil-water ratio also affected the stability of Pickering emulsion.Finally,ZNP-7.3 was used to emulsify the four oil phases that commonly used in cosmetics.The results showed that ZNP-7.3 had good emulsification performance for the oil,and Pickering emulsion with ethyl-hexyl-palmitate as oil phase had the best stability.