Effect Of Drying And Grinding On Properties Of Orange Dietary Fiber And Its Application

Orange is an important economic fruit in China.Orange peel is the main by-product during the orange processing,which is not effectively used.There is abundant carotenoid and dietary fiber in orange peel,especially soluble dietary fiber(SDF),which is a good source of dietary fiber.Orange dietary fiber was prepared from orange peel in this paper.The effects of drying methods and superfine grinding on structure,physicochemical and functional properties were studied and the correlation between physicochemical and functional properties was also discussed.The anti-diabetic effect of SDF on diabetic rat and its potential effect mechanism were studied.Moreover,effect of SDF on the release of metformin was studied.Research results were concluded as follows.1.The effects of drying methods on physicochemical and functional properties of dietary fiber.Soluble dietary fiber and insoluble dietary fiber(IDF)were prepared from orange peel,which were dried by hot air drying,vacuum drying and freeze-drying.Dietary fibers dried by hot air drying and vacuum drying exhibited compact structure and higher bulk density.Dietary fibers dried by freeze-drying exhibited loose structure with holes,larger specific surface area and lower bulk density.Drying methods had no significant effect on FTIR spectra,X-ray diffraction pattern and dietary fiber content of the dietary fiber samples,which indicated that the chemical structure and component of dietary fiber were not changed.Compared with hot air drying and vacuum drying,the water holding capacity,oil holding capacity and swelling capacity of SDF and IDF dried by freeze-drying were significantly enhanced.The viscosity of SDF dried by freeze-drying was the highest,followed by vacuum dried SDF.Drying methods had no significant effect on the viscosity of IDF.Hot air drying and vacuum drying might cause degradation of SDF backbone and decrease average molecular weight,which was consistent with the change of viscosity.Compared with hot air drying and vacuum drying,freeze-dried dietary fiber exhibited significantly higher glucose adsorption capacity.Drying method could affect the glucose dialysis retardation index,and freeze-dried dietary fiber significantly decreased glucose diffuse velocity at 10-300 min and exhibited higher glucose dialysis retardation index.The ?-amylase activity inhibition ratio of freeze-dried SDF and IDF was 34.60%and 15.95%,which was higher than hot air drying and vacuum drying.2.The effects of superfine grinding on physicochemical and functional properties of IDF.IDF was ground by regular laboratory milling,centrifugal milling and ball milling and the effect of grinding method on physicochemical and functional properties of IDF was studied.Both ultra centrifugal milling and ball milling could effectively decrease the average particle size of IDF,and ball milling worked better.Superfine grinding changed the microstructure of IDF,and the porosity structure of IDF partly disappeared.Superfine grinding had no significant effect on FTIR spectra and X-ray diffraction pattern of IDF.Superfine grinding changed fiber components,and some insoluble fiber turned into soluble fiber.Superfine grinding had negative effect on physicochemical properties of IDF,for example,water holding capacity,oil holding capacity and swelling capacity of IDF were decreased after superfine grinding.Ultra centrifugal milling and ball milling could enhance the lightness of IDF,which is beneficial to its application in light colored food.Superfine dietary fiber tended to have a greater number of particles per unit weight,indicating a higher dispersibility in food systems.Compared with regular milling,both ultra centrifugal milled IDF and ball milled IDF could decrease glucose diffuse velocity and delay glucose diffusion,and ball milled IDF worked better.Besides,both ultra centrifugal milling and ball milling could enhance the capacity of IDF to inhibit a-amylase activity.On the whole,superfine grinding could enhance the in vitro hypoglycemic effect of IDF to some extent.3.Anti-diabetic effect of SDF on diabetic rat and its potential effect mechanism.Type 2 diabetic rats were induced by high fat diet and low-dose STZ.In this study,citrus pectin could decrease FBG of diabetic rats,and hypoglycemic effect was dose-dependent.In the oral glucose tolerance test,medium-dose and high-dose could decrease AUC levels and suppress blood glucose peak values at 60 min.Citrus pectin decreased insulin resistance,TG,TC and LDL-c levels and increased HDL-c levels.Medium-dose and high-dose significantly increased hepatic glycogen contents,but had no significant effect on skeletal muscle glycogen contents.Histopathological examination of pancreas showed that citrus pectin had little effect on structure of pancreatic islets.The expression of p-Akt in liver was upregulated by citrus pectin and the expression of GSK3? was decreased,which indicated that citrus pectin might regulate the expression of key protein in insulin signal pathway.4.Effect of SDF on the release of metformin.SDF was used as matrix material to prepare gastroretentive floating metformin tablet.The contents of SDF and NaHCO3 in tablet were optimized using central composite design and response surface methodology.The mathematical model of the cumulative drug release to the contents of SDF and NaHCO3 in tablet was established.There was little difference between the observed value and the predicated value,which indicated that the model had a good predictability.The FTIR spectra and X-ray diffraction pattern showed that there is no significant incompatibility between the drug and SDF.SDF formed gel on the surface of the tablet in water,which would delay drug release.When the tablet was in gastric fluid,C02 was produced by NaHCO3 and wrapped by the gel,which would prolong the retention time in stomach and delay drug release.The drug release of the tablet prepared using SDF would last 10 h.The metformin release from the tablet followed Korsemeyer-Peppas model.The drug release mechanism is mainly diffusion controlled,and erosion happened at a later stage.