响应面试验优化小米糠膳食纤维改性工艺及其结构分析

Optimization of Modification Process for Millet Bran Dietary Fiber and Structural Elucidation

以小米糠为实验材料,对其进行气爆预处理,利用超声-微波协同法对气爆预处理的小米糠膳食纤维进行改性,以提高小米糠水溶性膳食纤维(soluble dietary fiber,SDF)的得率,并利用响应面法优化其工艺条件。同时借助凝胶色谱-示差-多角度激光光散射、红外光谱和X射线衍射等分析方法对改性前后小米糠膳食纤维的结构进行研究。结果表明:气爆条件设定为压力1.0 MPa、时间90 s,最优工艺参数为微波功率535 W、料液比1∶50(g/m L)、超声-微波协同时间57 min,SDF含量达到10.841%。凝胶色谱-示差-多角度激光光散射分析显示改性小米糠SDF分子质量变小,表明经改性处理后小米糠SDF分子链变短且聚合度降低。红外光谱分析表明,改性小米糠SDF和水不溶性膳食纤维(insoluble dietary fiber,IDF)的化学官能团变化不大,并且有明显的糖类特征吸收峰。X射线衍射分析显示改性小米糠IDF的结晶度上升,表明改性小米糠IDF中非结晶区有部分降解,并且转化为SDF。扫描电子显微镜结果显示改性小米糠SDF的颗粒表面变得粗糙,疏松多孔,由小颗粒聚集而成。

Millet bran was pretreated by steam explosion and then subjected to combined ultrasonic-microwave treatment in order to modify millet bran dietary fiber (MBDF), namely to increase soluble dietary fiber (SDF) yield. The process conditions were optimized using response surface methodology. In addition, the structures of modified and unmodified MBDF were investigated by means of gel permeation chromatography-refractive index-multi-angle light scattering (GPCRI-MALS), infrared spectroscopy and X-ray diffraction. The steam explosion conditions were set as 1.0 MPa and 90 s forpressure and time, respectively. The optimal conditions for combined ultrasonic-microwave treatment were determinedas microwave power of 535 W, solid-to-solvent ratio of 1:50 (g/mL) and time of 57 min, giving an SDF yield of as highas 10.841%. The results of GPC-RI-MALS showed that the molecular weight of modified millet bran SDF was smallerthat of the unmodified one, due to the shorter molecular chain and the reduced degree of polymerization resulted from themodification. The infrared spectroscopic analysis illustrated that there were no significant changes in the chemical functionalgroups between the modified SDF and IDF, and both of them possessed the characteristic absorption peaks of carbohydrates.The X-ray diffraction analysis revealed that the crystallinity of the modified IDF increased, indicating that its non-crystalline region was partially degraded and converted to SDF. Scanning electron microscopic (SEM) observation showed that the surface of modified millet bran SDF became rough, loose and porous and was composed of aggregated small particles.