| Tea polyphenol is a general term of the polyphenol compounds extracted from tea.Tea polyphenol,a kind of natural antioxidant,has many physiological functions such as decreasing the blood lipid.Small intestine is the main part to absorb tea polyphenol,however,the phenolic hydroxyl will be destroyed by gastric acid,microorganism and enzymes before tea polyphenol reaching small intestine,which leads to the loss of antioxidant activity.The bioavailability of tea polyphenol will be decreased.Debranched corn starch was prepared from normal corn starch using pullulanase in this paper.Xanthan-debranched corn starch complex carrier for sustained release of tea polyphenol microcapsule prepared using spray-drying improved the bioavailability and half-life of tea polyphenol.The effects of relative debranching degree and ratio of debranched corn starch to xanthan on the structure and properties of complex carriers and the sustained release property were studied in this paper.Animal experiment of decreasing blood lipid in rats was conducted using the microcapsule with the best in-vitro release effect,which confirmed that the microcapsule had a more significant hypolipidemic effect than directly utilizing tea polyphenol.The main contents of this paper are as follows:Firstly,four debranched corn starches with different relative debranching degrees were complexed with xanthan by mass ratio of 40:1 for microcapsule preparation.The in-vitro release result confirmed that the debranched starch with 34% debranching degree was a better choice for the preparation of microcapsule,release percents in simulated gastric and intestinal fluids were 30% and 80% respectively.The microcapsule with a smoother surface and smaller and more concentrated size distribution had a better release characteristic.When the complex ratio decreased,the release characteristic of microcapsule was worse,which was related to the structure of the complex carrier.The fitting result indicated that carrier dissolution dominating release process(release index n>0.85)was beneficial to the sustained release of microcapsule.The in-vitro sustained release result was further verified by the in-vivo experiment using rats.The better decreasing blood lipid effect of the microcapsule was consistent with the result of the in-vitro sustained release.Secondly,the relationship between structure properties of complex carrier and release characteristic was studied.The microstructure,crystalline structure,in-vitro digestibility,rheological and gel properties of complex carriers were studied.It was indicated that continuous,dense,porous and cross-linked network structure were more beneficial to the sustained release.The network structure played an important role in gel hardness,viscosity and shear resistance property of complex carrier.It was demonstrated that complex carrier with high viscosity and shear resistance was more beneficial to hinder the diffusion process of tea polyphenol.The in-vitro digestibility result indicated that resistant starch contents of complex carriers were all above 25%.However,there were no significant differences among the resistant starch contents,which indicated that the resistance of complex carrier was not the key factor that influenced the sustained release effect.Finally,the amylose and amylopectin contents,relative molecular weight and chain length distribution of debranched corn starch were researched.Relevance among structural properties of debranched corn starch,rheological and gel properties of complex carrier and release characteristic index were analyzed.The result indicated that increased amylose content,decreased relative molecular weight,molecular size and average chain length were achieved by moderate hydrolysis.The addition of xanthan increased the continuity and viscosity,but decreased the hardness and strength of complex carrier,which were beneficial to hinder the release of tea polyphenol from the microcapsule,and achieve the sustained release. |
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