ABSTRACT
Figure 23.1 (a) External view of the commercialized taste sensing system. (b) Extended view of connecter parts with sensor probes and the sensor chip. (c) Structure of the fabricated sensor chip.9 23.2.2 Lipid/Polymer MembraneA range of lipid/polymer membrane solutions with characteristics of saltiness, sourness, umami, bitterness, and astringency were prepared for both the taste sensor chip and the sensor probe. These consisted of plasticizers, lipids and polyvinyl chloride dissolved in 10 mL of THF for the detection of each taste substance.10,11 The components of the taste sensors were as follows: • Saltiness sensor: tetradodecylammonium chloride, n-tetradecyl alcohol, and dioctyl phenylphoshonate, • Sourness sensor: phosphoric acid di(2-ethylhexyl) ester, oleic acid, trioctylmethylammonium chloride, and dioctyl phenylphophonate • Umami sensor: phosphoric acid di(2-ethylhexyl) ester, trio-ctylmethylammonium chloride, and dioctyl phenylphopho-nate • Bitterness sensor: tetradodecylammonium chloride and dioctyl phenylphophonate
• Astringency sensor: tetradodecylammonium chloride and 2-nitrophenyl octyl ether 23.2.3 Standard Taste SubstancesIn this study, KCl, tartaric acid, MSG, iso-alpha acid, and tannic acid were chosen as standard taste substances to represent saltiness, sourness, umami, bitterness, and astringency, respectively. 23.2.4 Experimental ProcedureMeasurements were performed using the taste-sensing system TS-5000Z, and the conventional taste sensor probes (Intelligent Sensor Technology Inc., Japan) were used in comparison with the fabricated sensor chips. The fabricated taste sensor chip was connected to this taste-sensing system. An Ag/AgCl electrode with a single ceramic junction was used for measurement of the membrane potential as a reference electrode. Measurement procedures for the evaluation of the conventional taste sensor probes and the fabricated taste sensor chips were performed using the same procedure as described in the manual. A solution consisting of 30 mM KCl and 0.3 mM tartaric acid was used as a reference solution. A 30% ethanol aqueous solution containing 100 mM hydrochloric acid was used as the washing solution for the sensor probes and the sensor chips used for saltiness, sourness, and umami, while a 30% ethanol aqueous solution containing 100 mM potassium chloride and 10 mM potassium hydroxide was used for the bitterness and astringency modules. 23.2.5 Measurements of AftertasteThe taste sensors for bitterness and astringency can be measured aftertaste by monitoring of the adsorption of chemical substances onto the lipid/polymer membranes. The measurement procedure is called the “CPA” measurement (Change of membrane Potential caused by Adsorption). The CPA is key information for the evaluation of foods. In order to confirm the CPA measurements that were made using the fabricated sensor chips, the sensor responses of the sensor chips for bitterness and astringency were evaluated.
