β-Cyclodextrin/Surface Plasmon Resonance Detection System for Sensing Bitter-Astringent Taste Intensity of Green Tea Catechins

To develop a methodology for creating a sensor with a receptor for specific taste substances, we focused on constructing a sensing system for the bitter-astringent taste intensity of green tea catechins: (-)-epigallocatechin-3-O-gallate (EGCg), (-)-epicatechin-3-O-gallate (ECg), (-)-epigallocatechin (EGC), and (-)-epicatechin (EC). (1)H NMR titration experiments revealed that beta-cyclodextrin was an adequate receptor for sensing the bitter-astringent taste intensity of catechins. A surface plasmon resonance (SPR) system immobilized fi-cyclodextrin indicated larger responses for the gallate-type catechins in comparison to the non-gallate-type catechins. These responses corresponded to the tendency of the bitter-astringent taste intensity of the catechins felt by humans. Furthermore, the SPR system detected the larger stability of the complex between the gallate-type catechins and beta-cyclodextrin, which was interpreted as the aftertaste produced in humans by the gallate-type catechins. These results demonstrate that the beta-cyclodextrin/SPR system can sense the bitter-astringent taste intensity of the green tea catechins similar to human gustation. The methodology presented in this study can be used as a basic strategy for developing taste sensors with specific receptor functions.