Fabrication Of Structured Hydroxypropyl Methylcellulose Stabilized Emulsions And Encapsulation/Delivery Of Nobiletin

Natural polymethoxyflavones possess excellent biological activities.However,their bioavailability after oral administration is usually limited by their poor water-solubility and high crystallization.Emulsion-based delivery systems have been widely utilized in the solubilization,encapsulation and delivery of lipophilic functional components.Previous studies demonstrated that the incorporation of biopolymers in the emulsions could inhibit the crystallization of those components and prolong the retention time as a supersaturated state.Hence,hydroxypropyl methylcellulose?HPMC?was selected as the emulsifier to fabricate the emulsion systems.Then,whey protein concentrate?WPC?was incorporated to structurally modify HPMC stabilized-emulsions.The resultant emulsion systems were used to encapsulate and deliver lipophilic nobiletin?NOB?.The relationship between emulsion structure and NOB crystals and their stability was investigated.Finally,an in vitro digestion model was used to evaluate the bioaccessibility of NOB in the different structured emulsion systems.The knowledge from this study could provide the theoretical references for the fabrication of delivery systems for lipophilic nutraceuticals.The main results were listed as follows:1.To optimize the formulation of HPMC stabilized emulsions and to modulate the crystallization behavior and bioaccessibility of NOB.The best excipient of HPMC stabilized-emulsions was 20 wt% MCT and 3 wt% HPMC.The particle size of the obtained emulsions was around 300 nm.To study the crystallization behavior,9.0 mg/g NOB was loaded in the emulsions.The results demonstrated that The supersaturated state of NOB could be maintained at 4 oC and NOB crystals were adsorbed on the oil/water interface.HPMC could inhibit the migration of NOB from the oil phase to aqueous phase,improving the physical stability of NOB in the emulsions.When NOB initial concentration varied from 4.5 mg/g to 7.5 mg/g,the final retention concentration of NOB was around 4.5 mg/g.The bioaccessibility of NOB was independent on the NOB concentrations and more than 80%.2.Based on the precipitation of protein at the isoelectric point,structured HPMC/WPC emulsions and emulgels were fabricated by adjusting p H.Bioaccessibility of NOB in the structured emulsions was evaluated.The results demonstrated that when HPMC and WPC were used as the complex emulsifier,the retention concentration of NOB was 6.0 mg/g.That was higher than that in the HPMC?4.5 mg/g?or WPC?1.5 mg/g?stabilized emulsions.When p H was set at 4.5,lots of clusters were observed in the HPMC/WPC emulsion systems.This structure could form a coating layer on the surface of NOB,which inhibited the formation of NOB crystals.The retention concentration of NOB was 7.5 mg/g.At p H4.5,bioaccessibility of NOB was improved and kept to be more than 70%.3.Structured HPMC/WPC emulgels were produced by the cross-linking of Ca²⁺.Bioaccessibility of NOB in the structured emulsions was evaluated.The presence of HPMC could improve the stability of WPC stabilized emulgels,control the formation of gelling network and restrain the separating out of water.The results from micro rheology indicated that the viscoelasticity of WPC emulgels was weakened in the presence of HPMC.Polarized microscopy showed that NOB existed as small crystals,which were entrapped in the network.Ca²⁺ concentration could not only affect the structure of emulgels,but also affect the lipolysis process.For WPC-Ca²⁺ emulgel system,FFA% during digestion decreased as 0.12 wt% Ca²⁺>0.24 wt% Ca²⁺>0.50 wt% Ca²⁺>1.00 wt% Ca²⁺.While for HPMC/WPC-Ca²⁺ emulgel system,FFA% during digestion decreased as showed 0.50 wt% Ca²⁺>0.24 wt% Ca²⁺>0.12 wt% Ca²⁺>1.00 wt% Ca²⁺.The effect of Ca²⁺ concentration on the NOB bioaccessibility was similar as that on the FFA%.When Ca²⁺ concentration was 0.5 wt%,NOB in HPMC/WPC emulgels had the highest bioaccessibility,which was more than 70%.4.Comparison among different emulsion systems,HPMC as an emulsifier could delay the decrement of NOB concentration in the emulsion systems.Addition of WPC enhanced the loading amount of NOB from 4.5 mg/g to more 6.0 mg/g.Formation of emulgels,the encapsulation efficiency of NOB could be 100%.All of the three structured emulsion delivery systems could improve the bioaccessibility of NOB above 70%.