小米麸皮水溶性膳食纤维-Cr(Ⅲ)配合物的合成、表征及其体外抗氧化活性

Synthesis,Characterization and Antioxidant Activity of Millet Bran Soluble Dietary Fiber-Cr(Ⅲ)Complexes

采用酶法提取小米麸皮水溶性膳食纤维(soluble dietary fiber,SDF),并使SDF在弱碱性条件下与三价铬离子(Cr^(3+))发生配位反应,生成SDF-Cr(Ⅲ)配合物。运用扫描电子显微镜、傅里叶变换红外光谱、原子力显微镜对小米麸皮SDF和SDF-Cr(Ⅲ)配合物进行结构表征;运用常温凝胶渗透色谱及高效液相色谱(high performance liquid chromatography,HPLC)比较改性前后小米麸皮SDF分子质量分布及其单糖组成;通过测定1,1-二苯基-2-三硝基苯肼自由基、2,2’-联氮-双-3-乙基苯并噻唑啉-6-磺酸阳离子自由基、羟自由基清除率和总抗氧化能力,比较改性前后SDF体外抗氧化活性。结果表明:小米麸皮SDF-Cr(Ⅲ)配合物表面结构疏松,呈现出多孔状;岛屿状突起聚集度有所下降,分子间变得更加分散。两种SDF官能团差异较大,傅里叶变换红外光谱分析结果显示小米麸皮SDF-Cr(Ⅲ)配合物活性官能团(羟基、酯基、羰基等)伸缩振动减弱,特征吸收峰位置发生蓝移,在530.27 cm^(-1)处有Cr—O伸缩振动特征吸收峰,说明SDF与Cr^(3+)结合形成配合物。凝胶渗透色谱分析结果显示,SDF的数均分子质量(m+n)为0.195×10^(4) Da、重均分子质量(m_(w))为0.940×10^(4) Da、分布宽度指数D为4.81;SDF-Cr(Ⅲ)的m_(n)为0.742×10^(4) Da、m_(w)为4.708×10^(4) Da、分布宽度指数D为6.35。由HPLC分析结果可知,SDF-Cr(Ⅲ)单糖相对含量高于SDF。体外抗氧化实验结果表明,SDF-Cr(Ⅲ)比SDF具有显著的体外抗氧化性。综上,小米麸皮SDF-Cr(Ⅲ)配合物具有一定的抗氧化能力,具备开发成为具有降糖功效保健品的潜力。

Soluble dietary fiber(SDF)extracted from millet bran by enzymatic hydrolysis was coordinated with trivalent chromium ions in a weakly alkaline environment to produce SDF-Cr(Ⅲ)complexes.Scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR)and atomic force microscopy(AFM)were used to characterize the structures of SDF and SDF-Cr(Ⅲ)complexes.Gel permeation chromatography(GPC)and high-performance liquid chromatography(HPLC)were used to determine their molecular mass distribution and monosaccharide composition.Their in vitro antioxidant properties were measured by 1,1-diphenyl-2-trinitrophenylhydrazine(DPPH)radical,2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)(ABTS)radicla cation,and hydroxyl radical scavenging capacity and total antioxidant capacity.The results showed that the surface structure of SDF-Cr(Ⅲ)was loose and porous,exhibiting a decrease in the aggregation degree of island-like bulges and more scattered intermolecular arrangements compared to SDF.A large difference was found between SDF and SDF-Cr(Ⅲ)in functional groups.According to FTIR analysis,SDF-Cr(Ⅲ)showed reduced stretching vibrations of the active functional groups(hydroxyl,ester,and carbonyl groups),a blue shift in the absorption maximum,and a Cr-O stretching vibration at 530.27 cm^(-)1,confirming the binding Cr^(3+)to SDF.The number average molecular mass(m_(n)),weight average molecular mass(m_(w))and molecular mass distribution width index(D)of SDF was 0.195×10^(4) Da,0.940×10·4 Da,and 4.81,while those of SDF-Cr(Ⅲ)were 0.742×10^(4) Da,4.708×10^(4) Da and 6.35,respectively as determined by GPC.HPLC showed that the relative content of monosaccharides in SDF-Cr(Ⅲ)was higher than that in SDF.SDF-Cr(Ⅲ)had stronger in vitro antioxidant properties compared to SDF.In conclusion,millet bran SDF-Cr(Ⅲ)may have the potential to be developed into health products with hypoglycemic effect.