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

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（Cr3＋）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Cr3＋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（mn）为0.195×104 Da、重均分子质量（mw）为0.940×104 Da、分布宽度指数D为4.81；SDF-Cr（III）的mn为0.742×104 Da、mw为4.708×104 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。

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

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 Cr3+ to SDF. The number average molecular mass (mn), weight average molecular mass (mw) and molecular mass distribution width index (D) of SDF was 0.195 × 104 Da, 0.940 × 104 Da, and 4.81, while those of SDF-Cr(III) were 0.742 × 104 Da, 4.708 × 104 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.