摘要：
β-胡萝卜素广泛存在于植物体中, 是典型的线性多稀分子, 具有重要的生物功能.由于β-胡萝卜素是碳碳单、双键 (C—C, C=C) 交替的短链共轭多稀分子, 含有大量离域的π电子, 具有重要的光电特性.根据Andreas等对拉曼散射强度的研究, 当激发光波长落在分子的电子吸收带时, 会产生共振拉曼效应, 能使拉曼光谱强度提高106倍.利用共振拉曼光谱技术, 测量了β胡萝卜素分子及胡萝卜、青萝卜、白萝卜肉质直根不同部位其拉曼光谱, 发现含β-胡萝卜素较高的胡萝卜的拉曼光谱与β-胡萝卜素的吻合很好.Gellerman等研究表明, 样品浓度与拉曼峰强成正比关系, 从拉曼光谱中容易发现三种萝卜的光谱强度纵向根头到主根及横向表皮到根芯逐渐降低, 且青萝卜和白萝卜拉曼光谱强度都很低, 并在碳碳单键的振动峰处发生峰劈裂.分别计算了碳碳单键和碳碳双键与碳氢键拉曼强度比, 三种萝卜的ICC/IC—H随着测量部位 (横向和纵向) 的不同变化幅度接近:胡萝卜的表皮和根芯纵向的变化率分别为A1=0.213 3和A2=0.215 9, 青萝卜表皮外和里的变化率分别为B1=0.219 1和B2=0.211 4, 白萝卜表皮外和里分别为D1=0.223 9和D2=0.224 1;而对于IC—C/IC—H随着测量部位不同其变化率相差很大:胡萝卜的变化率a1=0.212 1和a2=0.232 4, 青萝卜的变化率b1=0.263 5和b2=0.268 7, 白萝卜的变化率d1=0.369 0和d2=0.304 9.对比发现三种萝卜的碳碳单键与碳氢键振动强度比随着测量部位的不同变化幅度相差很大, 而从碳碳双键与碳氢键振动强度比发现三种萝卜中不同部位的β胡萝卜含量有相似的分布.这是由于青萝卜和白萝卜中β-胡萝卜素的含量少, 随着测量部位的不同C—C伸缩振动峰发生峰劈裂, 即在1 130和1 156 cm-1处出现两个振动峰, 经过计算和分析这两个峰都属于碳碳单键的伸缩振动峰, 且随着β-胡萝卜素含量的减少C—C整体的强度降低, 劈裂的新峰峰强度却有增加的趋势, 这使得原峰位的峰强度大幅度降低, 这与计算IC—C/IC—H的结果一致, 不同品种的萝卜中β-胡萝卜素含量随测量部位的不同变化幅度截然不同.因此, 当样品中β-胡萝卜含量较少时, 利用C=C振动峰峰强度同时分析样品不同部位的β-胡萝卜素含量分布变化会更准确.同时, 研究和了解萝卜中不同部位β-胡萝卜素的含量为日常消费和膳食营养提供了很好的理论依据.%The β-carotene, with carbon-carbon single and double bonds (C—C, CC), is a typical linear polyenes, which widely exists in plants and has important biological function and plays an important role in investigating the π-electron conjugated properties. According to the Andreas' s study, when the exciting wavelength falls in electron absorption band, it will produce the resonance Raman effect and the Raman intensity can enhance 106 times. The Raman spectra of different parts of the carrot, white radish and green radish and the β-carotene are measured by using the resonance Raman spectroscopy, finding that the Raman spectra of carrot match well with β-carotene due to a high β-carotene content in carrots. Studies from Gellerman et al. show that the sample concentration is directly proportional to Raman peak intensity, which is clearly seen from the β-carotene Raman spectrum: the Raman intensity of three kinds of radish vertical root head to taproot and lateral skin to core gradually decrease, and the Raman intensity of C—C of the green and white radishes are lower and occur peak splitting. Calculating to intensity ratio of carbon-carbon single and double bonds to the carbon-hydrogen (C—H), the variation rates of ICC/IC—H of different measuring parts (horizontal and vertical) of three kind radish are close: the rates of change of epidermis and root core of carrot are A1=0.213 3 and A2=0.215 9, and the outside and inside of green radish are B1=0.219 1 and B2=0.211 4, and the outside and inside of white radish are D1=0.223 9 and D2=0.224 1; However, variation rates of IC—C/IC—H with the different measuring parts are greatly different: the carrot are a1=0.212 1 and a2=0.232 4, and the green radish are b1=0.263 5 and b2=0.268 7, and the white radish are d1=0.369 0 and d2=0.304 9. It is found that Raman intensity ratios of C—C to the C—H of three kinds with the different parts are greatly different, but the ratios of CC to C—H has similar distribution. This is due to the low levels of β-carotene in green and white radishes, the vibrational peak of C—C occurs peak splitting, namely, two vibrational peaks appear at 1 130 and 1 156 cm-1. As the amount of β-carotene decrease, the intensity of C—C peak reduces, and the intensity of new peak is induce, making the peak intensity of the original peak greatly reduce. This is consistent with the results of IC—C/IC—H. Therefore, using the Raman intensity of C=C to analyze the β-carotene content of different parts is more accurately. Furthermore, studies of the content of the β-carotene in different parts of radish can help to provide a good theoretical basis for daily consumption and dietary nutrition.
