Detection of flavor substances using surface plasmon resonance with lipid LB membranes

The technique using the phenomenon called surface plasmon resonance can make it possible to detect the change of refractivity (or dielectric constant) of a solution in a thin local region (the typical thickness of the region is about 1 μm), which is very close to the surface of a thin basal metal plate. Interactions between lipid molecules and flavor substances were investigated by using the surface plasmon resonance. In this study, the effects of various kinds of flavor substances - which can be regarded as representative of the five kinds of basic tastes (sweet, salt, sour, savory, and bitter) - on the lipid membranes were examined. The lipid membrane utilized as a receptor for taste substances was the LB (Langmuir-Blodgett) multilayered film composed of dihexadecyl phosphate. It was found that almost no flavor substances had any observable interactions to the lipid membrane system, while quinine hydrochloride, the representative of bitterness, was found to be strongly adsorbed to the lipid membrane. It was shown by doing measurements for various numbers of layers of the membrane system that the quinine hydrochloride is absorbed not only onto the surface but into the internal region of the lipid layers. It was observed that the sweet substance or salty substance suppressed the adsorption of the bitter substance. Similar suppression effects can also be found in biological systems.