Shu Ezaki

Objective scaling of taste of sake using taste sensor and glucose sensor

Abstract The taste of Japanese sake was investigated using a taste sensor with eight kinds of lipid membranes and an enzymatic glucose sensor. The electric-potential pattern constructed of eight outputs from the taste sensor has information on the taste quality and intensity. A standard solution for sake measurement was synthesized. Therefore, chemical meanings were assigned to two perpendicular axes transformed from the nine variables of outputs from the two sensors; commercial brands of sake were scattered on this plane. The taste of sake was discussed objectively.

Self-Sustained Oscillations of Membrane Potential in DOPH-Millipore Membranes

Self-sustained oscillations of membrane potential in an artificial model membrane, where dioleyl phosphate (DOPH) is infiltrated into pores of a Millipore filter, are investigated both experimentally and theoretically. Spike-like self-oscillations with an extremely long period of about one hour were observed for membranes with large adsorbed amounts of DOPH in the absence of external forces such as electric current and pressure gradient. On the basis of a previously-presented model that DOPH molecules make transitions among three phases composed of oil droplets, spherical micelles and multi- or bilayer leaflets, the occurrence of self-oscillations is explained well by taking account of an accumulation and a release of salt in a pore of the filter.

Study of astringency and pungency with multichannel taste sensor made of lipid membranes

Abstract Pungent and astringent substances have been studied using a multichannel taste sensor. The electric-potential pattern made up of eight outputs from the membranes of the sensor has information about taste quality and intensity. Pungent substances including capsaicin, piperine and allyl isothiocyanate have no effect on the electric potentials of the liquid membranes. On the other hand, astringent substances such as catechin, tannic acid, chlorogenic acid and gallic acid change the potentials remarkably. A principal-component analysis of the patterns in electric-potential change caused by the taste substances reveals that the taste quality of astringency is located between bitterness and sourness. A model for astringency is presented.

Peculiar change in membrane potential of taste sensor caused by umami substances

Monosodium glutamate (MSG) induces a favorable taste, termed umami. The action of MSG on lipid membranes of a taste sensor was investigated. In general, food constituents monotonously increase the electric potential of the negatively charged membranes. Contrary to this, MSG decreases the potential at lower concentration and increases it at higher concentration, thus the effect of MSG on lipid membrane is biphasic. On the decrease of the membrane potential, a model was proposed in which the dissociated carboxyl group of MSG accelerates the dissociation of phosphate group of the membrane lipid.

Growth and electric current flowing at the surface of stems

SummaryEffect of electric current flowing at the surface of stem of bean (Phaseolus angularis) on the growth was studied using an electric isolation between the elongation and mature regions. The growth was retarded by the electric isolation because of change in pH distribution around the stem, associated with decreasing surface electric current. Electric current flowing at the surface between the elongation and mature regions is important for the growth of stems.

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.