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甜味是食品科學(xué)的一個(gè)基本問(wèn)題，甜味感官特征的評(píng)價(jià)一直依賴于人的感官品評(píng)。由于品評(píng)人員個(gè)體、性別及閱歷等生理和心理的差異，對(duì)味覺(jué)客觀、真實(shí)感受的表達(dá)存在著很大的制約性。而且，基于實(shí)驗(yàn)條件的限制和甜味感覺(jué)的特殊性，人們至今沒(méi)有完整理解甜味分子的感受機(jī)理。而在甜味抑制劑研究方面，雖然人們對(duì)甜味抑制劑作用位點(diǎn)達(dá)成了共識(shí)，但有關(guān)甜味抑制物質(zhì)起作用的機(jī)制是競(jìng)爭(zhēng)性的還是非競(jìng)爭(zhēng)性的，仍然沒(méi)有統(tǒng)一的結(jié)論。 本課題組前期以富勒醇C60(OH)18作為人工甜味化學(xué)受體模型，運(yùn)用等溫滴定量熱（ITC）方法探索甜味識(shí)別的熱力學(xué)，研究結(jié)果表明富勒醇對(duì)人工甜味劑、天然甜味劑都具有較好的識(shí)別效果，其作為模型化合物研究甜味機(jī)理具有可行性。本論文進(jìn)一步運(yùn)用感官品評(píng)、ITC、核磁共振（NMR）和分子模擬（MS）等多種實(shí)驗(yàn)手段共同研究人工甜味受體模型與甜味抑制劑，甜味異構(gòu)體、甜味增強(qiáng)劑的識(shí)別作用，以期獲得甜味機(jī)理方面更多的信息。 本課題研究的內(nèi)容有： （1）人工甜味化學(xué)受體模型與甜味抑制劑作用的研究 采用甜味抑制劑（HPMP）和十四種常用甜味劑，通過(guò)前期建立的人工甜味受體模型ITC滴定模式，獲得抑制過(guò)程中熱力學(xué)參數(shù)，實(shí)驗(yàn)結(jié)果表明富勒醇優(yōu)先自發(fā)識(shí)別HPMP，疏水作用力在識(shí)別過(guò)程中起著重要作用，HPMP和甜味劑同富勒醇的結(jié)合具有競(jìng)爭(zhēng)性。 同時(shí)采用“快速作用-有無(wú)法”的品評(píng)模式進(jìn)行HPMP感官實(shí)驗(yàn)，通過(guò)比較加入甜味抑制劑前后甜味劑察覺(jué)閾值，發(fā)現(xiàn)HPMP對(duì)不同結(jié)構(gòu)甜味劑的抑制效果不同，離子對(duì)其作用無(wú)明顯影響，抑制效果可以用Ik（甜味抑制度）量化表示。 比較富勒醇識(shí)別過(guò)程中熱力學(xué)參數(shù)與Ik，發(fā)現(xiàn)熱力學(xué)平衡常數(shù)的比值（K1/K2）與Ik有一定的相關(guān)性，K1/K2比值越大，甜味抑制度Ik越高，由此佐證了甜味抑制機(jī)理可能是甜味抑制物質(zhì)競(jìng)爭(zhēng)與味蕾受體結(jié)合產(chǎn)生的。實(shí)驗(yàn)結(jié)果進(jìn)一步說(shuō)明利用人工受體模型研究甜味機(jī)理的有效性。 （2）人工甜味受體模型與甜味劑異構(gòu)體作用的研究 通過(guò)ITC、NMR和MS等技術(shù)共同研究富勒醇與單糖異構(gòu)體的作用，實(shí)驗(yàn)結(jié)果表明在溶液中多種單糖異構(gòu)體共存的情況下，富勒醇與β型異構(gòu)體結(jié)合更穩(wěn)定，優(yōu)先與之形成氫鍵，此過(guò)程中釋放出的能量可以提供α型異構(gòu)分子轉(zhuǎn)化成β型異構(gòu)分子所需的構(gòu)象轉(zhuǎn)化能，打破溶液中原有的變旋平衡，向生成β型異構(gòu)體的方向移動(dòng)，導(dǎo)致溶液中β型異構(gòu)體比例明顯增加。因此可以推測(cè)，單糖分子接近味蕾受體時(shí)，可能也引起甜味劑異構(gòu)體的平衡移動(dòng)，導(dǎo)致異構(gòu)體的比例發(fā)生變化，具體表現(xiàn)為各種糖類異構(gòu)體的甜度差異。 （3）人工甜味化學(xué)受體模型與甜味增強(qiáng)劑作用的研究 通過(guò)MS手段進(jìn)行富勒醇分子與甜味增強(qiáng)劑的相互作用的研究，結(jié)果表明甜味增強(qiáng)劑與富勒醇形成氫鍵后，還與甜味分子形成較強(qiáng)氫鍵，這樣就拉近了甜味分子與富勒醇的距離，增強(qiáng)了甜味分子與富勒醇的氫鍵強(qiáng)度，使其更好地與富勒醇進(jìn)行識(shí)別。因此可以推測(cè)，甜味增強(qiáng)劑在與味蕾受體結(jié)合的同時(shí)，還能與甜味分子形成較強(qiáng)氫鍵，從而增強(qiáng)了甜味分子與味蕾受體的識(shí)別作用，實(shí)際表現(xiàn)為增強(qiáng)劑單獨(dú)使用不產(chǎn)生甜味，但和甜味劑共同使用能有效增強(qiáng)甜感。 （4）不同結(jié)構(gòu)的人工甜味受體模型與甜味劑相互作用的研究 通過(guò)分子動(dòng)力學(xué)模擬，對(duì)現(xiàn)有人工甜味受體模型C60(OH)18進(jìn)行結(jié)構(gòu)優(yōu)化，實(shí)驗(yàn)結(jié)果表明富勒醇隨碳數(shù)增加碳球籠體積增大，在理想稀溶液中，分子表面疏水作用力增加，無(wú)法更好與甜味分子識(shí)別；富勒醇羥基數(shù)的增加會(huì)使其與單糖分子的結(jié)合能增加，識(shí)別作用更加明顯，但是羥基數(shù)過(guò)多會(huì)減小分子表面疏水作用力，分子表面的羥基因?yàn)榫嚯x過(guò)近會(huì)相互吸引形成分子內(nèi)，增大識(shí)別過(guò)程中噪音能量，不利于多羥基富勒醇分子與單糖分子的識(shí)別作用。因此，結(jié)構(gòu)優(yōu)化結(jié)果表明C60(OH)20更適合作為人工甜味受體模型。 總之，本文在前期研究的基礎(chǔ)上，采用多種實(shí)驗(yàn)手段，進(jìn)一步利用富勒醇作為人工甜味受體的模型化合物研究了它與甜味劑異構(gòu)體、甜味抑制劑和甜味增強(qiáng)劑的相互作用，在目前人們未能獲得甜味蛋白精細(xì)結(jié)構(gòu)之前，研究結(jié)果對(duì)于理解甜味識(shí)別、甜味抑制機(jī)理和甜味增強(qiáng)機(jī)理具有一定的意義，同時(shí)也豐富了甜味機(jī)理研究的仿生化學(xué)。 |
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木子小木蟲:本版嚴(yán)禁軟件翻譯，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樓2010-11-10 17:36:01
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