作物淀粉晶体结构的波谱分析

摘要

作物淀粉有A-型、B-型和C-型晶体,本文利用粉末X-射线衍射仪(XRD)和固体核磁共振波谱仪(13C CP/MASNMR)研究了不同植物来源淀粉的波谱特征和相对结晶度.结果表明,水稻、马铃薯和豌豆淀粉分别表现典型的A-型、B-型和C-型晶体XRD波谱,荸荠淀粉则表现CA-型XRD波谱,葛根淀粉为CB-型XRD波谱.以Jade 5.0分析软件峰拟合法和曲线作图法计算出来的淀粉XRD相对结晶度差别较大,且无相关性,以曲线作图法计算出来的相对结晶度可信度较高.不同来源淀粉的13C CP/MAS NMR波谱相似,有C1、C4、C2,3,5和C6区域,区别主要在C1区域,在该区域A-型糯玉米和普通玉米淀粉有3个结晶峰,B-型马铃薯淀粉有2个结晶峰,CA-型转基因高直链水稻(TRS)淀粉有3个不明显的结晶峰,而CB-型酸解TRS淀粉有2个结晶峰,无定形淀粉没有结晶峰.利用PeakFit 4.12峰拟合分析软件能够计算淀粉13C CP/MAS NMR波谱的相对结晶度和双螺旋含量,其中双螺旋含量比结晶度高,结晶度又比依据XRD波谱计算出来的结晶度高.上述研究结果为应用XRD和13C CP/MAS NMR波谱技术分析作物淀粉晶体结构提供了重要参考.%Crop starches have A-type, B-type, and C-type crystallinity, and C-type crystallinity is the combination of both A-type and B-type crystallinity. In this paper, spectrum characteristics and relative crystallinity of starches from different plants were investigated with X-ray powder diffraction (XRD) and 13C cross-polarization magic-angle spinning nuclear magnetic resonance (13C CP/MAS NMR). The results indicated that rice, potato and pea starches showed typical A-type, B-type, and C-type XRD spectra respectively. Water chestnut starch showed a CA-type XRD spectrum, which was a C-type closer to A-type. Kudzu starch showed a CB-type XRD spectrum, which was a C-type closer to B-type. The relative crystallinity of starch from XRD was obtained using the Jade 5.0 software and the curve mapping method. The results of two methods showed significant difference and had no correlation. The crystallinity with the curve mapping method was more reliable. The spectra of 13C CP/MAS NMR from different crop starches showed similar characteristics, and had four regions of C1, C4, C2, 3, 5 and C6, while the difference of the spectra among different starches was from Cl region. In Cl region, A-type starches of waxy and normal maize showed three peaks, B-type starch of potato showed two peaks, the transgenic resistant starch rice line (TRS) starch, which was a CA-type crystallinity, showed three inconspicuous peaks, the acid-modified TRS starch with CB-type crystalline showed two peaks and the amorphous starch had no peaks. The 13C CP/MAS NMR spectra were peak fitted by using the PeakFit 4.12 software. The relative crystallinity and the percentage of double helix content in starches were calculated. The double helix content was higher than the relative crystallinity. The crystallinity obtained from 13C CP/MAS NMR was higher than that from XRD. These results would be very useful for the application of XRD and 13C CP/MAS NMR to the analysis of crystalline structure of crop starches.