| Through hydrophobic modification, polysacchariades can spontaneously self-assemble in water to form self-aggregates. The formation of micellelike aqueous self-assemblies with a hydrophobic core and hydrophilic shell depends on the repelling and coordinating forces between the hydrophilic and hydrophobic parts of amphiphiles. These self-assemblies are versatile tools in pharmacy, food, and daily chemical industries and are capable of trapping hydrophobic pharmaceuticals and active components in their core. This characteristic increases solubility/dispersity and prevents rappid degradation of trapped components. Finally, these self-assemblies can competent for the target delivery and controlled release of bioactive compounds. To our best knowledge, few studies have investigated the application of β-glucan as substrates in the formation of functional self-assemblies. Thus, esterification by octenylsuccination was adopted to prepare hydrophobic oatβ-glucan. This work mainly focused on the interaction between octenylsuccinate oat β-glucan (OSG) self-assemblies and lipophilic food components. Futhermore, the stability, targeted-release profiles and bioavailability of lipophilic food components loaded OSG were also evaluated.(1) OSG was synthesised through the esterification reaction between oat β-glucan and 2-octen-1-ylsuccinic anhydride. The influences of reaction time and temperature, the addition amount of 2-octen-l-ylsuccinic anhydride, and oat β-glucan concentration on degree of substitution (DS) of OSG were investigated. Based on single factor experiments, a series of central composite design experiments were conducted for an optimal synthesis process. Oat β-glucan concentration, reaction time and temperature were selected as variables and a mathematical regression model for DS was developed. Finally, the optimal extraction process was:oat β-glucan concentration 2.18 mg/mL, reaction time 4.66 h, and reaction temperature 45.6 ℃. New bands were observed in the Fourier Transform infrared (FT-IR) spectrometry and nuclear magnetic resonance (NMR) analysis of OSG. Differential scanning calorimeltry (DSC) showed that ΔH of oat β-glucan was higher than that of OSG. Thermo gravimetric analyzer (TGA) revealed that the thermal stability of OSG was higher than that of oat oat β-glucan.(2) Dynamic light scattering (DLS) and transmission electron microscopy (TEM) revealed that OSG can self-assemble into spherical micelles in water with an average size ranging from 175 to 600 nm. Fluorescence spectroscopy indicated that the critical micelle concentration (CMC) of OSGs varied from 0.206 to 0.039 mg/mL, depending on the DS and Mw of the OSG. An increase in DS results in a sharp decrease in the CMC of OSG. This finding is attributed to the enhanced hydrophobicity of OSG with its elevated DS. Lower molecular weight polymers have lower steric hindrances, which facilitate the chance of contact among hydrophobic chains in self-assemblies, compared with that of higher molecular weight polymers. Thus, a decrease in the CMC of OSG (from 0.206 mg/mL to 0.081 mg/mL) with a decrease in the Mw of oat β-glucan was observed. Structural (DS and Mw) parameters of OSG, as well as environment (pH, temperature, ionic strength and OSG concentration) could significantly affect the self-assembly behavior of OSG.(3) The dependence of the curcumin loading capacity (CLC) of octenylsuccinate oat β-glucan (OSG) micelles on the structural parameters and environment was explored in this study. Our study revealed that curcumin was physically entrapped in the micelles through the hydrophobic interaction between the aromatic groups of curcumin and octenyl succinate groups of OSG. CLC maximized at medium DS and decreased as DS increased or lowered. However, CLC increased with the increase of Mw. Under optimal conditions (DS= 0.0199 and Mw= 1.68×105 g/mol), the maximum CLC of OSG micelle was 4.21 ±0.16μg/mg. Meantime, solubilization of curcumin by OSG micelles was also influenced by the environment factors. First, CLC of OSG micelles increased as IP (Input power) increased from low input power levels to high input power levels. Second, CLC also depend on the OSG concentration, pH and temperature. Maximum curcumin concentration (CC) in the OSG micelle solution was obtained as 21.16±0.66μg/mL under the optimized conditions (IP=4.4 W, stirring time= 96 h, temperature=35.7℃, pH=5.9, and OSG concentration=2.57 mg/mL).(4) These shifted and disappeared vibrations in the FT-IR spectra of curcumin-loaded OSG compared with curcumin and the physical mixture are evidences for the successful loading of curcumin into OSG micelles. DSC and X-ray diffraction revealed that curcumin was loaded in OSG micelles in an amorphous form by interacting with OSG molecules. DLS, TEM and atomic force microscopy (AFM) revealed that the size and PDI of micelles formed by OSG showed a significant decrease and irregular surface of micelles were formed after curcumin incorporation due to the stronger hydrophobic interaction between curcumin and OSG.(5) To investigate the effects of structure of polyphenols on their interaction with OSG,26 flavonoids and 10 phenolic acids were used in this study. The number and position of hydroxylation, methylation, and glycosylation in polyphenols significantly affected the loading capacity of polyphenols into OSG micelles. Among flavonoid isomers, their solubilizing efficiencies increased in the order:flavonol> flavone> isoflavone> flavanone. Glycosylation significantly improved the loading capacity of flavonoids into OSG micelles. The loading capacity of baicalin, myricetrin, rutin, daidzin, genistin, and naringin into OSG micelles was 5391.3%,4744.7%,288%,385.2%,140.3%, and 276.4% higher than those of baicalein, myricetin, quercetin, daidzein, genistein, and naringenin, respectively. The order of loading capacity of coumaric acid into OSG micelles was:o-coumaric acid> m-coumaric acid>p-coumaric acid. Galloylation of EC and EGC, resulting in ECG and EGCG, significantly decreased their solubilizing capacities.(6) The in vitro stability and release profiles and bioavilability of curcumin loaded OSG micelles were investigated. Meantime, the food process and storage stability of curcumin loaded OSG micelles and their application in fruit juice also investigated. Our study revealed that OSG micelles could effectively protect the curcumin from the high pH in simulated intestinal fluid compared with the contrast. The fast release of curcumin from OSG micelles proved that OSG micelles could be used as a colon-targeted delivery system for bioactive food compounds/components, compared with the low release rate of curcumin from OSG micelles in simulated gastro-intestinal fluids. The bioavilability of curcumin could be significantly improved by OSG micelles through comparing concentrations of curcumin present in the plasma. The improved bioavilability of curcumin by OSG could be ascribed by the effective protection of curcumin during its travel in digestive tract and good mucoadhesive of OSG.(7) The curcumin loaded in OSG micelles showed better food process stability (under light and UV irradiation, and heat treatment) than in methanol-water (5:95, v/v) solution. The Ea for curcumin loaded OSG micelles in juice increased in the order:pawpaw (41.57 kJ/mol)>pineapple (35.11 kJ/mol)>cantaloupe (34.9 kJ/mol). The curcumin loaded OSG micelles incorporated juice stored at 4 ℃ showed better curcumin retention than 25 ℃. Curcumin degradation in all juice followed zero and first-order reaction kinetics when it stored at 4 and 25 ℃. Curcumin showed a much faster degradation rate during storage at room temperature than did in refrigerated temperature. |
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