Fabrication And Application Of Edible Delivery Systems Using Zein/Caseinate And Its Derivatives

Food bioactive component is a large class of food composition with important biological activities.However,the direct applications of those bioactives in food are restricted by their low solubility in aqueous environment,poor physico-chemical stability,pungent smell,interactions with food ingredients(such as protein,fat)and ultimately low bioavailability.Encapsulation of those bioactives in self-assembled nanoparticles using edible biological macromolecules is a promising approach to solve the above problems.Zein is ideal for preparing nanoparticles due to its unique molecular structure and self-assembly property.Sodium caseinate(NaCas)can be used to improve the stability of zein nanoparticles in the aqueous environment due to its good water solubility.Because these two materials are recognized as safe(GRAS)food additives,they have good prospects for application as the carrier materials for food bioactives.In order to provide scientific evidences for the possible application of Zein and NaCas in other delivery systems,we selected two representative food bioactives——thymol and curcumin,fabricated and evaluated their delivery systems using Zein and NaCas as the main carrier materials.Thymol-loaded Zein-NaCas nanoparticles were fabricated using the optimized liquid-liquid dispersion method.Based on the optimum mass ratio of Zein to NaCas(1:1),the nanoparticles were prepared with the diameter of 204.75 nm,zeta potential value of-35.10 mV,encapsulation efficiency of 65.75% and spherical morphology.Moreover,thymol-loaded Zein-NaCas nanoparticles showed the sustained antimicrobial effect against Staphylococcus aureus,compared to that of free thymol.By coating a positively charged chitosan hydrochloride(CHC)layer onto the surface of thymol-loaded Zein-NaCas nanoparticles,the obtained double-coated zein nanoparticles had an improved encapsulation efficiency and stronger antimicrobial effect.Curcumin-loaded Zein-NaCas nanoparticles were fabricated with the diameter of 187.16 nm,zeta potential value of-36.43 mV,encapsulation efficiency of 95.55% and the spherical core-shell structure.In vitro release behavior showed that curcumin released from the nanoparticles by diffusion.Fourier transform infrared(FTIR)indicated that the encapsulated curcumin interacted with zein mainly through hydrophobic interactions.Compared to free curcumin,the stabilities for the encapsulated curcumin under UV irradiation and high temperature heating treatment were significantly improved.Besides,the encapsulated curcumin had a stronger inhibitory effect on the growth of Caco-2 cells,with the curcumin concentration range of 10-50 ?M.Cellular uptake and transport studies revealed that the encapsulated curcumin was taken up to a greater extent and transported more efficiently through Caco-2 monolayer.Structural modification of some edible proteins through enzymatic or chemical method seems to be an effective approach to improve their physico-chemical,functional properties and extend their applicabilities as the delivery carriers.Besides,it is also important for the development of new carrier materials.We used enzymatic and chemical modification methods to conjugate nonpolar alkyl chains into the molecular structures of NaCas,respectively.Then,the physico-chemical,functional and self-assembly properties of the modified caseinate were studied.A novel microbial transglutaminase(MTGase)-catalyzed aqueous-organic biphasic reaction system was successfully developed to prepare the caseinate derivatives by incorporating octyl tails into NaCas.The octyl substitution degree(5.22-28.96%)was controlled by the reaction conditions,such as the concentration of NaCas and reaction time.The obtained octyl-conjugated caseinate had an increased molecular weight,which was due to the intra-/inter molecular cross-linkings.Increased surface hydrophobicity index,better emulsifying activity and improved thermal and salt stabilities were also observed for the modified caseinate.Octyl-and hexadecyl-conjugated caseinate derivatives without molecular cross-linkings were successfully syntheized by using a mild and safe chemical modification method.By controlling the reaction condition,we obtained caseinate derivatives with different alkyl substitution degrees.The surface hydrophobicity index of caseinate derivatives increased with the increase of alkyl substitution degree.Compared to the unmodified NaCas,hexadecyl-conjugated caseinate derivatives had better self-assembly properties,and the formed self-assemblies had better curcumin loading capacities.The detailed capacities included: increased encapsulation efficiency,better assembly appearance and desirable redispersibility.