Development of Taste Sensor to Detect Non-Charged Bitter Substances

Abstract

A taste sensor with lipid/polymer membranes is one of the devices that can evaluate taste objectively. However, the conventional taste sensor cannot measure non-charged bitter substances, such as caffeine contained in coffee, because the taste sensor uses the potentiometric measurement based mainly on change in surface electric charge density of the membrane. In this study, we aimed at the detection of typical non-charged bitter substances such as caffeine, theophylline and theobromine included in beverages and pharmaceutical products. The developed sensor is designed to detect the change in the membrane potential by using a kind of allosteric mechanism of breaking an intramolecular hydrogen bond between the carboxy group and hydroxy group of aromatic carboxylic acid (i.e., hydroxy-, dihydroxy-, and trihydroxybenzoic acids) when non-charged bitter substances are bound to the hydroxy group. As a result of surface modification by immersing the sensor electrode in a modification solution in which 2,6-dihydroxybenzoic acid was dissolved, it was confirmed that the sensor response increased with the concentration of caffeine as well as allied substances. The threshold and increase tendency were consistent with those of human senses. The detection mechanism is discussed by taking into account intramolecular and intermolecular hydrogen bonds, which cause allostery. These findings suggest that it is possible to evaluate bitterness caused by non-charged bitter substances objectively by using the taste sensor with allosteric mechanism.

Effect of Hydroxybenzoic Acids on Caffeine Detection Using Taste Sensor with Lipid/Polymer Membranes

“…In the study [35], the interactions between caffeine and HBA were formed by intermolecular hydrogen bonds (e.g., the O-H(carboxy) N(imidazole) hydrogen bond). On the basis of this result, the study [13] has discussed the mechanism of caffeine detection as the following: owing to intermolecular hydrogen bonds between HBAs and caffeine, the carboxyl groups of HBAs removed H + from the caffeine solution, which caused allostery. The allostery resulted in a change in membrane potential, which is used as the response to caffeine.…”

“…In our previous study [13], non-charged bitter substances (e.g., caffeine, theophylline, and theobromine) were measured using taste sensors with lipid/polymer membrane modified with HBAs, and this method is similar to those which improve the sensitivity of sweet taste sensors to sugar by surface modification [14,15]. In the literature [13], caffeine detection has been discussed as a change in membrane potential due to allostery caused by intermolecular hydrogen bonds between HBAs and caffeine. Moreover, the sensitivity of taste sensors to caffeine detection has been related to the number of intramolecular hydrogen bonds of HBAs.…”

Study on taste characteristics and microbial communities in Pingwu Fuzhuan brick tea and the correlation between microbiota composition and chemical metabolites

“…Studies indicated that alkaloids such as caffeine, theophylline, and theobromine provided bitter taste in teas, and caffeine was a main contributor to bitterness. Furthermore, flavonoids, catechins, and certain amino acids including L -histidine, Llysine, L -valine, L -tryptophan, L -arginine, L -tyrosine, Lphenylalanine, L -isoleucine, and L -leucine, contributed to bitter taste in teas (Yang et al 2018;Zou et al 2018;Yoshimatsu et al 2020). L -Theanine, L -glutamic acid, L -glutamine, L -aspartic acid, and L -asparagine contributed to the umami taste (Yang et al 2018).…”

Electrical Properties of Two Types of Membrane Component Used in Taste Sensors

“…The average of the third to fifth measurement cycle was calculated as the response value. The standard deviations were calculated from n = 4 (sensor electrodes) × 3 (cycles) = 12 values in the same way as previous studies [10,17,20,27].…”