Study On The Characteristics And Activities In Vitro Of Soluble Dietary Fiber Of Black And White Glutinous Rice Bran

Dietary fiber posses abundant physiological activities,which can regulate the levels of blood glucose and blood lipid,preventing cardiovascular disease,obesity and colon cancer et al.However,there is still a gap in research which is focused on physiological activity of soluble dietary fiber from glutinous rice bran at home and abroad,including its mechanism.In this paper,black glutinous rice bran with rich anthocyanins and common white glutinous rice bran used as raw materials,and soluble dietary fiber(SDF)from rice bran was extracted by enzymatic removal of starch and protein.The physical and chemical properties,structural characterization and vitro bioactivity of two kinds of SDF were compared.The purpose of this study was to explore the potential mechanism of SDF in decreasing the blood glucose levels in vitro after the meal,with the research of glucose digestion and absorption in vitro and the interaction between SDF and the enzymes of starch digestion.Thus we believe that this research may provide a reference basis for the application and the development of related products of rice bran from different sources.The results were obtained as follows:(1)Comparison of raw materials of rice bran:The content of protein,fat and ash in black glutinous rice bran was higher than that of white glutinous rice bran.Black glutinous rice bran contained 5.34%SDF,while about 7.26%SDF in white glutinous rice bran.Comparison of SDF1 and SDF2:The percent of anthocyanins,reducing sugar,total sugar in the soluble dietary fiber 1(SDF1)from black glutinous rice bran was 6.42%,12.24%,75.17%respectively,but about 17.53%reducing sugar and65.88%total sugar in the soluble dietary fiber 2(SDF2)from white glutinous rice bran,which did not contain anthocyanin.The purity of the two kinds of SDF were more than 90%.The results of free polyphenols in the rice bran,SDF and insoluble dietary fiber(IDF)were indicated that the polyphenol in the rice bran was enriched in SDF,and the content of free phenol in SDF1 was 10.31 mg/g,which was 1.32 times of SDF2.The properties of SDF showed that the viscosity of SDF1 was higher than that of SDF2,but the solubility was lower than that of SDF2.The initial and the maximum pyrolysis temperature of SDF2 were higher than that of SDF1 by thermal stability analysis was performed by differential scanning calorimetry(DSC),which indicated that SDF2 had better thermal stability.The average relative molecular mass of SDF1and SDF2 were 3057,3018 respectively.According to the analysis of UV-VIS and IR spectra,the biggest difference was the characteristic absorption peak of anthocyanin from SDF1.The analysis of neutral monosaccharide composition illustrated that the highest percent of monosaccharide from two kinds of SDF was glucose,and its contents in SDF1 was higher than SDF2.Through the scanning electron microscopy,the surface structure of SDF1 was loose and had a regular porous structure with an average pore size of 4.22±0.55?m,while the surface of SDF2 was smoother and only has localized size of 3.10±0.72?m.Observing the state of the two species of SDF in the aqueous solution,the assembly of aggregated particles of SDF1 was found to be greater than that of SDF2.(2)The anti-oxidative ability of SDF in vitro revealed that,the order of the anti-oxidative ability was Vc,SDF1,SDF2,which indicated that both two kinds of SDF had a certain antioxidant capacity and SDF1 was showed better.The simulative experiment of adsorbing glucose in vitro showed that the two kinds of SDF had a certain ability to adsorb glucose,and SDF1 was significantly greater than SDF2;the comparison of the capacity to inhibit glucose diffusion in vitro found that two varieties of SDF can also inhibit the glucose diffusion and SDF1showed stronger inhibition than that of SDF2.However,the simulative experiments of starch digestion and directly interaction with?-amylase in vitro indicated that the ability of inhibiting starch digestion ability of SDF2 in vitro was higher than that of SDF1,and its inhibition rate of?-amylase was 43.07%,which about 2.25 times of SDF1.(3)The interaction between SDF and starch digestion enzymes(?-amylase and amyloglucosidase)was studied using fluorescence spectroscopy and circular dichroism.And we also compared the interactions between SDF and two kinds of enzymes.It turned out that the two kinds of SDF and the fluorescent substance from the two varieties of starch digestion enzymes came into being the complexes through static quenching,forming a binding site.And the binding constant K_a between SDF1and the two kinds of enzymes was greater,so the degree of integration may be more considerable.But the interaction force was not the same.SDF1 interacted with?-amylase by hydrogen bonding and van der Waals'forces,while the forces between SDF2 with?-amylase was electrostatic attraction.In addition,the interaction force between the two kinds of SDF and amyloglucosidase was also different.The interaction force between SDF1 and amyloglucosidase was hydrophobic,while SDF2 relied on hydrogen bonding and van der Waals'forces to interact with amyloglucosidase.Both two kinds of SDF created redshifts of the maximum emission wavelength of amyloglucosidase,which indicated that the conformation of amyloglucosidase was changed.SDF1 and SDF2 were confirmed to play a role in changing the secondary structures of two kinds of starch digestion enzymes by circular dichroism analysis.