The Mechanistic Researches Of Sweet Recognition Based On An Artificial Sweet Tast Receptor Model

Sweet taste is a basic issue of food science while evaluation of sweetness organoleptic property always relies on panelist sensory evaluation. Nobody has completely understood sense mechanism of sweet molecules due to limited experimental condition and specialty of sweet taste. Although researchers have made some agreement on acting spot of sweetness inhibitor in relating researches, there's still no uniformed conclusion regarding whether sweetness inhabiting mechanism is competitiveness or not.Recently, our team used C60(OH)18 as a synthetic sweetness receptor model, and isothermal titration calorimetry (ITC) as a tool to discover the thermodynamic mechanism of the molecular recognition of sweetness. The result showed a fullerenols-based synthetic model can effectively recognize both artificial and natural sweeteners. Our model truly helps to understand the mechanism of the recognition of sweetness.This thesis further applies multiple experimental approaches such as sensory evaluation, ITC, NMR(Nuclear Magnetic Resonance) and MS(molecular simulate) to research on recognition of artificial receptor model, sweetness inhibitor, sweetness isomer and sweetness enhancer in order to obtain more information about mechanism of sweetness. The main research work is as follows:(1) Research on Artificial Receptor Model and Sweetness InhibitorThe thermodynamics of the mimetic interaction of HPMP and 14 sweeteners with fullerenols as a synthetic sweet receptor model was elucidated by ITC technique. Thermodynamic parameters revealed that fullerenols recognize HPMP firstly on account of hydrophobic force, and competitive binding with fullerenols do exist when the sweeteners and HPMP are presented in the solution concurrently."rapid action-yes or no way" sensory evaluated method was conducted to get the threshold value of each sweetener. The efficiency of HPMP inhibiting each sweetener was expressed by the change of sweetness intensity. Test result implied that the inhibitor showed discriminating inhibition effect on each sweet compound, and ion has no significant effect on suppressive effectivity (Ik)The combined results of sensory evaluation and ITC thermodynamics revealed that the larger value of the ratio of two equilibriums constant K1/K2, the more effectively HPMP inhibit the sweetness of the sweetener. Thus the results proof that maybe the HPMP suppressive effect on human sweet taste by a competitive mechanism. Further certification of the artificial sweet receptor is a useful model that helps to provide chemical information of sweetness recognized mechanism.(2) Research on Artificial Receptor Model and Sweetness IsomersReaction of fullerenols and monosaccharides isomer is jointly researched by application of ITC, NMR and MS technology. Experimental result shows that fullerenols andβ-isomer has more stable coalition and can form hydrogen bond preferentially while multiple monosaccharides isomers existing in solution at meantime. Such process can release necessary conformation conversion energy for a-isomers transfer intoβ-isomers thus to break original mutarotation balance of solution and shift toward generating direction ofβ-isomers, causing significant increase ofβ-isomers in solution. Therefore it can be attributed that monosaccharides molecular may cause equilibrium shifting of sweet isomer when approaching taste buds receptors, then proportion change of isomer may incur and specifically expressed as sweetness difference of various sweet isomers.(3) Research on Artificial Sweetness Chemical Receptor Model and Sweetness EnhancerResearches on interactions of fullerenols module and sweetness reinforcing agent has been conducted by MS approach. The result shows that sweetness reinforcing agent can form relatively strong hydrogen bond after forming hydrogen bond with fullerenols,hence, distance between sweet module and fullerenols is shortened while hydrogen bond intensity of sweet module and fullerenols is improved for better recognition with fullerenols. It can be estimated that sweet reinforcing agent can form relatively strong hydrogen bond while combing with taste buds receptor to improve recognition of sweet module and taste buds receptor.(4) Research on Interactions Between Artificial Sweet Receptor Model with Different Structures and EdulcoratorStructural optimization of artificial sweetness receptor model C60(OH)18 by molecular dynamics simulation shows that fullerenols grows along with enlarging size of carbon spheres. Hydrophobic interaction increases on module surface in idea diluted solution; therefore we're unable to make better identification with sweetness module. Increasing fullerenols hydroxyl groups will improve binding energy of monosaccharides molecular and more obvious recognition, but excessive hydroxide numbers will decrease hydrophobic interaction increases on module surface. Hydroxid on module surface will make interaction to form intramolecular and increase noise energy during recognition process, therefore make against to recognition reaction of polyhydroxy fullerenols module and monosaccharides molecular. Hence, structural optimization result shows that C60(OH)20 is more suitable to be used as artificial sweetness receptor model.In conclusion, the thesis applies multiple experimental approaches to further study interactions among fullerenols which is used as model compound of artificial sweetness receptor, edulcorator isomer, sweetness inhibitor and sweetness reinforcing agent. The research result has certain significance for people to understand sweetness inhibitor, sweetness inhibiting mechanism and sweetness strengthening mechanism before as certaining fine structure of sweet protein while also enriches biomimetic chemistry of sweetness mechanism study.