Hidekazu Ikezaki

Multichannel taste sensor using electric potential changes in lipid membranes

A taste sensor with a multichannel electrode was developed by using lipid membranes as a transducer of taste substances. The sensor can detect the taste in a similar manner to the human gustatory sensation by response patterns of electric potential to taste substances. The sensitivity, reproducibility and durability were superior to those of humans. The same taste as that elicited by some commercial aqueous drink was reproduced by making aqueous solution mixed from four kinds of basic taste substances, the concentrations of which were determined so that the electric-potential pattern of this mixed solution could agree well with the pattern by the drink. Different brands of beer were easily distinguished by the electric-potential patterns.

Evaluation of the bitterness of antibiotics using a taste sensor

The bitterness of nine commercial antibiotics (clarithromycin, erythromycin, cefdinil, doxycycline, vancomycin, tetracycline, minocycline, oxytetracycline and bacampicillin) was evaluated in human gustatory sensation tests with nine volunteers. The bitterness of 0.1–0.3 mM solutions (or suspensions in the case of clarithromycin) of the antibiotics was then measured using an artificial multichannel taste sensor. In the sensor measurements, three variables were used to predict estimated bitterness in single and multiple regression analysis and principal component analysis: sensor output as relative value (R), the change of membrane potential caused by adsorption (C) and C/R. Particularly good correlation was obtained between obtained bitterness scores and predicted scores using C from channel 2 of the sensor (r2 = 0.870, P < 0.005) and C/R values for channels 2 and 3 (r2 = 0.947, P < 0.005). The taste sensor was also successful in assessing the bitterness intensity of clarithromycin powder suspensions of various concentrations. Clarithromycin has a low aqueous solubility but is the most bitter of the nine antibiotics. Sensory data from channel 3 of the sensor predicted the bitterness of clarithromycin powder suspensions and their filtered solutions well. Finally, the bitterness intensity of a commercial clarithromycin dry syrup product (Clarith dry syrup, Taisho Pharmaceutical Co. Ltd, Tokyo, Japan) was evaluated in gustatory sensation tests and using the taste sensor. In Clarith dry syrup the drug is coated with aminoalkyl methacrylate polymer using a spray congealing method. The taste sensor results confirmed that the polymer was successful in almost completely masking the bitter taste of the dry syrup product.

Prediction of the bitterness of single, binary- and multiple-component amino acid solutions using a taste sensor

The purpose of this study was to develop a quick, quantitative, prediction method for the determination of the bitterness of solutions containing one or more of five amino acids (L-isoleucine, L-leucine, L-valine, L-phenylalanine, and L-tryptophan), using an artificial taste sensor. The bitterness of various solutions containing different concentrations (1, 3, 10, 30, and 100 mM) of five amino acids, singly and in combination, was estimated using a multichannel taste sensor and compared with the results of human gustatory sensation tests with nine volunteers. The relative response electric potential patterns were similar for all five amino acids. Large sensor outputs were observed in channels 1-4 (which are negatively charged) while there were no responses in channels 5-8 (positively charged). The sensor output for channel 1, which was the largest output value, was used for prediction of bitterness. The change of membrane potential caused by adsorption (CPA), which corresponds to aftertaste, could not be used as an explanatory variable since the adsorption of the amino acids to the sensor membrane was weak and CPA values were small. The bitterness intensity scores for single, binary, and multi-component amino acid solutions, could be easily predicted on the basis of the sensor output value of channel 1 using regression analysis. Principal component analysis of the sensor output data suggested that the sourness, astringency and/or smell of the solutions also played a role in the perception of bitterness.

Electric characteristics of lipid-modified monolayer membranes for taste sensors

Abstract Lipid membranes are useful materials to transform information about taste substances into electric signals. A lipid monolayer membrane for a taste sensor has been prepared by adsorbing lipid materials to the hydrophobic surface of a polymer membrane. The lipid-modified membranes respond to such electrolytic taste substances as HCl (sourness) or NaCl (saltiness) with large response magnitudes and such non-electrolytic substances as caffeine (bitterness) or sugar (sweetness) with high sensitivities. Thus the present membrane has a high ability to detect taste.

Analysis of sake mash using multichannel taste sensor

The titrable acidity of and the ethanol concentration in sake mash were measured using a multichannel taste sensor system. A positively charged membrane responded to ethanol and the electric response of the membrane showed good agreement with those determined by gas chromatography in the measurement of sake mash. It was considered that the responses were induced by a change in the activity coefficient of anions. The titrable acidity of sake mash was measured using an electrode with a negatively charged membrane, because the electric response of the membrane showed a strong correlation with the titrable acidity of sake. The result showed good agreement with the value determind by titration, and the agreement was slightly increased by multiple regression together with the electric response of the positively charged membrane. Therefore, it is concluded that this method is useful for determination of the ethanol concentration in and the titrable acidity of sake mash. The results show that the taste sensor can be used for monitoring of those values in sake fermentation.

Development of a Sweetness Sensor for Aspartame, a Positively Charged High-Potency Sweetener

Taste evaluation technology has been developed by several methods, such as sensory tests, electronic tongues and a taste sensor based on lipid/polymer membranes. In particular, the taste sensor can individually quantify five basic tastes without multivariate analysis. However, it has proven difficult to develop a sweetness sensor, because sweeteners are classified into three types according to the electric charges in an aqueous solution; that is, no charge, negative charge and positive charge. Using membrane potential measurements, the taste-sensing system needs three types of sensor membrane for each electric charge type of sweetener. Since the commercially available sweetness sensor was only intended for uncharged sweeteners, a sweetness sensor for positively charged high-potency sweeteners such as aspartame was developed in this study. Using a lipid and plasticizers, we fabricated various lipid/polymer membranes for the sweetness sensor to identify the suitable components of the sensor membranes. As a result, one of the developed sensors showed responses of more than 20 mV to 10 mM aspartame and less than 5 mV to any other taste. The responses of the sensor depended on the concentration of aspartame. These results suggested that the developed sweetness sensor had high sensitivity to and high selectivity for aspartame.

Relationship between the amount of bitter substances adsorbed onto lipid/polymer membrane and the electric response of taste sensors.

The bitterness of bitter substances can be measured by the change in the membrane electric potential caused by adsorption (CPA) using a taste sensor (electronic tongue). In this study, we examined the relationship between the CPA value due to an acidic bitter substance and the amount of the bitter substance adsorbed onto lipid/polymer membranes, which contain different lipid contents, used in the taste sensor. We used iso-α-acid which is an acidic bitter substance found in several foods and beverages. The amount of adsorbed iso-α-acid, which was determined by spectroscopy, showed a maximum at the lipid concentration 0.1 wt % of the membrane, and the same phenomenon was observed for the CPA value. At the higher lipid concentration, however, the amount adsorbed decreased and then remained constant, while the CPA value decreased monotonically to zero. This constant adsorption amount was observed when the membrane potential in the reference solution did not change with increasing lipid concentration. The decrease in CPA value in spite of the constant adsorption amount is caused by a decrease in the sensitivity of the membrane as the surface charge density increases. The reason why the peaks appeared in both the CPA value and adsorption amount is based on the contradictory adsorption properties of iso-α-acid. The increasing charged lipid concentration of the membrane causes an increasing electrostatic attractive interaction between iso-α-acid and the membrane, but simultaneously causes a decreasing hydrophobic interaction that results in decreasing adsorption of iso-α-acid, which also has hydrophobic properties, onto the membrane. Estimates of the amount of adsorption suggest that iso-α-acid molecules are adsorbed onto both the surface and interior of the membrane.

Evaluation of palatability of 10 commercial amlodipine orally disintegrating tablets by gustatory sensation testing, OD‐mate as a new disintegration apparatus and the artificial taste sensor

The purpose of this study was to evaluate and compare the palatability of 10 formulations (the original manufacturers formulation and nine generics) of amlodipine orally disintegrating tablets (ODTs) by means of human gustatory sensation testing, disintegration/dissolution testing and the evaluation of bitterness intensity using a taste sensor.

Analysis of a Lipid/Polymer Membrane for Bitterness Sensing with a Preconditioning Process.

It is possible to evaluate the taste of foods or medicines using a taste sensor. The taste sensor converts information on taste into an electrical signal using several lipid/polymer membranes. A lipid/polymer membrane for bitterness sensing can evaluate aftertaste after immersion in monosodium glutamate (MSG), which is called “preconditioning”. However, we have not yet analyzed the change in the surface structure of the membrane as a result of preconditioning. Thus, we analyzed the change in the surface by performing contact angle and surface zeta potential measurements, Fourier transform infrared spectroscopy (FTIR), X-ray photon spectroscopy (XPS) and gas cluster ion beam time-of-flight secondary ion mass spectrometry (GCIB-TOF-SIMS). After preconditioning, the concentrations of MSG and tetradodecylammonium bromide (TDAB), contained in the lipid membrane were found to be higher in the surface region than in the bulk region. The effect of preconditioning was revealed by the above analysis methods.

An advanced technique using an electronic taste-sensing system to evaluate the bitterness of orally disintegrating films and the evaluation of model films

Taste detection systems using electronic sensors are needed in the field of pharmaceutical design. The aim of this study was to propose an advanced technique using a taste-sensing system to evaluate the bitterness of an orally disintegrating film (ODF) samples. In this system, a solid film sample is kept in the test medium with stirring, and the sensor output is recorded. Model films were prepared using a solution-casting method with a water-soluble polymer such as pullulan, HPMC, HPC or PVP as film formers, and donepezil hydrochloride and quinine hydrochloride as model bitter-tasting active pharmaceutical ingredients (APIs). The results showed that this advanced techniques could detect the emergence of bitterness along the time course. Increasing the amount of donepezil hydrochloride increased the sensor output. The sensor output was suppressed at the very early stage of the test, and then increased. Both the film thickness and the use of additives markedly affected the delay of the sensor output. The profile of the sensor output was accurately related to the release of APIs. It was concluded that this advanced technique could detect the onset of bitterness during the initial stage of ODF administration.