The Thermodynamics Study Of Sweet Recognition Based On Sweet Receptor Model

Sweet taste is a basic issue of taste perception. Before the complete crystal structure of the human taste receptor proteins being disclosed, evaluation of sweet taste property is always mainly relying on panelist sensory evaluation which is easily influenced by individual diffierence of panelist on physiology and psychology. Therefore, it is valuable to study perceived sweetness and break down the mechanisms of sweet recognition using model system.In our previous study, we introduced a new strategy using polyhydroxylated C60(fullerenols) as the model compound to elucidate the key interactions involved in sweeteners and sweet receptor. Using this biomimetic approach, we found that the thermodynamic parameters obtained from isothermal titration calorimetry(ITC) correlated well with the sweet intensity of different sweeteners and the thermodynamic basis of the initiation of sweetness inhibition. In this context, we measured the association constant of enantiomorphic pairs binding with the sweet taste receptor model, therefore to find the underlying thermodynamic basis of different sweetness intensity of sweetener enantiomers. And we also investigated the interaction between sweetener and the sweet taste receptor model in the presence of hydrocolloid in order to understand the the effect of macromolecular crowing on sweetness sensation. Based on the results from artificial receptor model, we extended our study on thermodynamics invovled sweet recognition using sweet receptor cell.(1) The interaction between sweetener enantiomorphs and the sweet taste receptor modelWe use fullerenols as an artificial sweet taste receptor model to investigate the binding affinities of D-and L-enantiomorphs of three monosaccharides and four amino acids by isothermal titration calorimetry(ITC) in order to find the relationship of the thermodynamics in the mimetic receptor-ligand binding with sweetness intensity. Moreover, fourier transformation infrared spectroscopy (FT-IR) was used to find the binding sites of enantiomorphs with fullerenols. The results indicated that the higher the perceived sweetness intensity of the enantiomer, the larger binding constant with respect to their antipodes.(2) The interaction between sweetener and the sweet taste receptor model in hydrocolloid system We investigated thermodynamics of the binding between aspartame and fullerenols which was used as an artificial sweet taste receptor model in guar gum and sodium carboxymethyl cellulose (CMC-L) in order to find the effect of other physical properties such as viscosity, random-coil of polysaccharides and water activity on thermodynamics and sweetness intensity relationship. The results showed that the higher viscosity, the lower binding affinities in both hydrocolloid systems, but there was no clear relationship between viscosity, random-coil of polysaccharides and sweetness intensity. Water activity of thickened system and the enthalpy (△H1) in the binding of aspartame with fullerenols were found correlated to the sweetness intensity of aspartame:the lower water activity and binding enthalpy, the lower sweetness intensity of aspartame. The hydrocolloid might influence the binding enthalpy by changing the condition of hyrated shell of aspartame and then resulted in declined sweetness intensity.(3) The thermodynamics of sweet recognition based on sweet receptor cellThe thermodynamics of saccharin binding with sweet receptor cell were studied and the application of ITC in complex cell suspension was also discussed. The binding constant of saccharin and real receptor was found to be104M-1.