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甜味是食品科学的一个基本问题，甜味感官特征的评价一直依赖于人的感官品评。由于品评人员个体、性别及阅历等生理和心理的差异，对味觉客观、真实感受的表达存在着很大的制约性。而且，基于实验条件的限制和甜味感觉的特殊性，人们至今没有完整理解甜味分子的感受机理。而在甜味抑制剂研究方面，虽然人们对甜味抑制剂作用位点达成了共识，但有关甜味抑制物质起作用的机制是竞争性的还是非竞争性的，仍然没有统一的结论。 本课题组前期以富勒醇C60(OH)18作为人工甜味化学受体模型，运用等温滴定量热（ITC）方法探索甜味识别的热力学，研究结果表明富勒醇对人工甜味剂、天然甜味剂都具有较好的识别效果，其作为模型化合物研究甜味机理具有可行性。本论文进一步运用感官品评、ITC、核磁共振（NMR）和分子模拟（MS）等多种实验手段共同研究人工甜味受体模型与甜味抑制剂，甜味异构体、甜味增强剂的识别作用，以期获得甜味机理方面更多的信息。 本课题研究的内容有： （1）人工甜味化学受体模型与甜味抑制剂作用的研究 采用甜味抑制剂（HPMP）和十四种常用甜味剂，通过前期建立的人工甜味受体模型ITC滴定模式，获得抑制过程中热力学参数，实验结果表明富勒醇优先自发识别HPMP，疏水作用力在识别过程中起着重要作用，HPMP和甜味剂同富勒醇的结合具有竞争性。 同时采用“快速作用-有无法”的品评模式进行HPMP感官实验，通过比较加入甜味抑制剂前后甜味剂察觉阈值，发现HPMP对不同结构甜味剂的抑制效果不同，离子对其作用无明显影响，抑制效果可以用Ik（甜味抑制度）量化表示。 比较富勒醇识别过程中热力学参数与Ik，发现热力学平衡常数的比值（K1/K2）与Ik有一定的相关性，K1/K2比值越大，甜味抑制度Ik越高，由此佐证了甜味抑制机理可能是甜味抑制物质竞争与味蕾受体结合产生的。实验结果进一步说明利用人工受体模型研究甜味机理的有效性。 （2）人工甜味受体模型与甜味剂异构体作用的研究 通过ITC、NMR和MS等技术共同研究富勒醇与单糖异构体的作用，实验结果表明在溶液中多种单糖异构体共存的情况下，富勒醇与β型异构体结合更稳定，优先与之形成氢键，此过程中释放出的能量可以提供α型异构分子转化成β型异构分子所需的构象转化能，打破溶液中原有的变旋平衡，向生成β型异构体的方向移动，导致溶液中β型异构体比例明显增加。因此可以推测，单糖分子接近味蕾受体时，可能也引起甜味剂异构体的平衡移动，导致异构体的比例发生变化，具体表现为各种糖类异构体的甜度差异。 （3）人工甜味化学受体模型与甜味增强剂作用的研究 通过MS手段进行富勒醇分子与甜味增强剂的相互作用的研究，结果表明甜味增强剂与富勒醇形成氢键后，还与甜味分子形成较强氢键，这样就拉近了甜味分子与富勒醇的距离，增强了甜味分子与富勒醇的氢键强度，使其更好地与富勒醇进行识别。因此可以推测，甜味增强剂在与味蕾受体结合的同时，还能与甜味分子形成较强氢键，从而增强了甜味分子与味蕾受体的识别作用，实际表现为增强剂单独使用不产生甜味，但和甜味剂共同使用能有效增强甜感。 （4）不同结构的人工甜味受体模型与甜味剂相互作用的研究 通过分子动力学模拟，对现有人工甜味受体模型C60(OH)18进行结构优化，实验结果表明富勒醇随碳数增加碳球笼体积增大，在理想稀溶液中，分子表面疏水作用力增加，无法更好与甜味分子识别；富勒醇羟基数的增加会使其与单糖分子的结合能增加，识别作用更加明显，但是羟基数过多会减小分子表面疏水作用力，分子表面的羟基因为距离过近会相互吸引形成分子内，增大识别过程中噪音能量，不利于多羟基富勒醇分子与单糖分子的识别作用。因此，结构优化结果表明C60(OH)20更适合作为人工甜味受体模型。 总之，本文在前期研究的基础上，采用多种实验手段，进一步利用富勒醇作为人工甜味受体的模型化合物研究了它与甜味剂异构体、甜味抑制剂和甜味增强剂的相互作用，在目前人们未能获得甜味蛋白精细结构之前，研究结果对于理解甜味识别、甜味抑制机理和甜味增强机理具有一定的意义，同时也丰富了甜味机理研究的仿生化学。 |
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木子小木虫:本版严禁软件翻译，警告 2010-11-11 11:10:50
| Sweet is a basic problem of food science, the evaluation of the sensory characteristics of sweet taste has been dependent on the sensory evaluation. The evaluation of individual staff, such as gender and experience physical and psychological differences, the objective of the Taste, the expression of true feelings of the existence of significant constraints. Moreover, based on the experimental conditions, the special restrictions and sweet feeling, it has not felt the full understanding of the molecular mechanism of sweet taste. In the sweetness inhibitors, although one site on the sweetness inhibitor reached a consensus, but work on the mechanism of sweet taste inhibitor is competitive or non-competitive, and still no uniform conclusions. Early in our group fullerols C60 (OH) 18 as a chemical receptor model of artificial sweetness, using isothermal titration calorimetry (ITC) method to explore the thermodynamic sweet recognition, the results show that artificial sweeteners fullerenol, natural sweeteners have a good recognition effect, its mechanism of sweetness as a model compound with a feasibility study. The paper further use of sensory evaluation, ITC, nuclear magnetic resonance (NMR) and molecular simulation (MS) and other experimental methods to study with the sweetness receptor model of artificial sweetness inhibitors, isomers sweet, sweet enhancer Recognition, in order to obtain more information mechanism are sweet. The contents of this research are: (1) chemical receptor model of artificial sweetness sweetness sweetness inhibitor effect of inhibitors used (HPMP) and fourteen commonly-used sweeteners, artificial sweetness through the pre-established by the ITC titration model body model, inhibition of the process to obtain the thermodynamic parameters, experimental results show that self-identify priority fullerenol HPMP, hydrophobic interactions in the recognition process plays an important role, HPMP and sweetener with the combination of fullerenol competitive . At the same time a "fast effect - there can not be" tasting mode HPMP sensory experiments, by comparing before and after adding inhibitor sweetener sweetness threshold detection and found that the structure of different sweeteners HPMP the inhibitory effect of different ions on the role of non- significant effect, inhibitory effect can Ik (sweet suppression degree) to quantify said. Comparison Fullerenols thermodynamic parameters of the process of identifying and Ik, found that the ratio of the thermodynamic equilibrium constant (K1/K2) and Ik have some relevance, K1/K2 ratio the greater the degree of sweetness suppression Ik higher, thus supporting the inhibition mechanism may be the sweet sweet taste buds of competition and inhibition of receptor-binding material produced. The results further explanation of the use of artificial sweet taste receptor model the effectiveness of the mechanism. (2) artificial sweeteners sweet receptor models and the role of isomers by ITC, NMR, and MS Fuller and other technologies to study alcohol and the role of monosaccharide isomers, experimental results indicate that a variety of single-solution isomer coexistence of sugar, the Fuller alcohol combined with the β-isomer is more stable, priority with the formation of hydrogen bonds, this process can provide the energy released α-β-isomer molecules into heterogeneous elements conformational transition required to break the Central Plains and some change spin balanced solution to generate β-isomers of direction, leading to β-isomers in solution was significantly increased. Can therefore speculate that a single sugar molecule close to the taste bud receptors may also lead to the equilibrium shift isomers sweeteners, leading to changes in the ratio of isomers, is specifically expressed in a variety of differences between the sweetness of sugar isomers. (3) chemical receptor model of artificial sweetness enhancer and the effect of sweet taste by molecular MS fullerols means interaction with the sweetness enhancer, the results show that the sweetness enhancer and the formation of hydrogen bonds fullerenol later, also with the sweet molecules form strong hydrogen bonds, so sweet closer the distance between alcohol molecules and Fuller, Fuller enhanced sweet alcohol molecules and the hydrogen bond strength, making it better with Fuller alcohol for identification. So you can guess, sweetness enhancers and taste buds in the same receptor, but also strong and sweet molecules form hydrogen bonds, thus increasing the sweet taste receptor molecules and identify the role of taste buds, the actual performance of the enhancer alone does not produce sweet, but the common use, and sweeteners can enhance the sweet feeling. (4) different structures of the human sweet taste receptor model of the interaction with sweetener by molecular dynamics simulation, artificial sweet taste receptor model of the existing C60 (OH) 18 to optimize the structure, experimental results show that fullerenol With the increase in the number of carbon Carbon Cage volume increase, in an ideal dilute solution, the molecular surface hydrophobic interactions increase with the sweetness of molecular recognition can not be better; Fuller hydroxyl increase in the number of single sugar molecules to the binding energy increased recognition is more obvious, but too much will reduce the number of hydroxyl hydrophobic molecular surface, molecular surface hydroxyl groups as too close to be attracted to each other to form molecules, the increase in the noise energy of the recognition process is not conducive to polyhydroxy Fuller alcohol molecules and the role of molecular recognition of monosaccharides. Therefore, the structural optimization results show that the C60 (OH) 20 is more suitable for human sweet taste receptor model. In short, this paper, based on previous studies, using a variety of experimental methods, further use of artificial sweet fullerenol receptor as model compound to study its isomer with the sweeteners, sweetness inhibitors and sweetness enhancers interaction, people are not given in the current fine structure of the sweet protein before, the results for the understanding of sweetness recognition, inhibition mechanism and the sweet sweet enhancement mechanism has a certain significance, but also enrich the mechanism of the biomimetic chemistry sweet . |
2楼2010-11-10 17:36:01