Malini Basu11th GradePine Crest School

Gustatory system in humans consists of direct chemoreceptors called taste buds Taste buds, located in groups in taste papilla are activated

in response to stimuli in solid and liquid foods

Five basic tastes identified by different receptors on the tongue are salty, sweet, bitter, sour and savory

Half of the papilla on the tongue are sensitive to all the basic tastesHalf are sensitive to only one kind of tasteWhen a food molecule comes into contact with a taste bud, it

induces a chemical response that triggers stimuli in the nervous system to alert the brain of a taste

Used primarily for food and beverage quality analysis

Allows for the quantification of quality analysis Smaller and more economical than methods such as gas chromatography,

mass spectroscopy, and high performance liquid chromatography Parts of the ET

5 metal working electrodes which allow current to pass through the sample solution (Gold, iridium, rhodium, palladium, and platinum)

Using a variety of metal electrodes takes into consideration any reactive ion species in solution

Stainless steel counter electrode through which the current flows out of the sample Ag/AgCl is the reference electrode to which the electric potential between the

working and counter electrode is compared This electrode consists of a thin Ag wire surrounded by AgCl solution

Working Electrodes

Reference electrode

Counter electrode

Top view

Important commodity especially in Asian country Quality depends on Polyphenol concentrations

Theaflavins (TF) and Thearubigins (TR) are the two groups of polyphenols that affect tea flavor significantly

Processing Oxidation is the most important process

Oxidized polyphenols affect tea flavor Physical damage to cell walls in previous steps allows for enzymes within the cell walls to stimulate oxidation. Oxidation of polyphenols creates the defining characteristics of different tea varieties.

Converting polyphenol catechins to TF and TR Amount of oxidation defines quality of tea

The tea industry has expert panels who assign different grades based on tea quality

Catechin

To identify the Electronic Tongue’s capability of differentiating between 10 samples of varying grades of Black Tea.

Basic Taste Test Tool to visualize the way the ET distinguishes between

different flavors Large Amplitude Pulse Voltammetry applied to basic

taste inducing solutions and tea samples Applies voltage potential in different amplitudes to the system to

induce different current values due to reduction or oxidation of a species

If redox active species is reduced at electrode surface reaction is A + ne- A-

At standard conditions this reaction has a standard potential E0 can be used to establish a correlation b/w the concentration of the oxidized (Co) and the reduced form (Cr) according to the Nernst equation:

Eelectrode = E0 + RT/nF (ln(Co / Cr)) 5 trials each per sample Each working electrode is individually accessed in the

cell

Taste Compound Example

Sweet Sucrose: C12H22O11 Candy

Salty Sodium Chloride: NaCl Salted potato chips

Bitter Sodium Hydroxide: NaOH

Caffeine in coffee

Sour Citric Acid: C6H8O7 Lemons

Umami (Savory)

Glutamic Acid: C5H9NO4 Red Meat

Demonstration of the ET’s ability to distinguish between the 5 basic tastes as well as water as a ‘neutral’ taste. The clustering of each of the 5 trials establishes the accuracy of these results. The ET was able to consistently differentiate between each of the solutions.

At about 4.5 uC of charge the average strength of

response was 6,700 for the NaOH solution (bitter)NaCl

(salty)

C6H8O7

(Sour)

C5H9NO4

(Savory)

C12H22O11

(sweet)

H2O

Sample Number Grades

1 7/13 DM – Dust Mixed

2 BP – Broken Pekoe

3 PF – Pekoe Fannings (highest quality)

4 D – Dust (lowest quality)

5 8/13 DM – Dust Mixed

6 BP – Broken Pekoe

7 PF – Pekoe Fannings

8 D – Dust

9 10/13 DM – Dust Mixed

10 BP – Broken Pekoe

There is a linear correlation between the quality of each tea sample, and the strength of response. The highest quality (PF, sample 7) had the strongest charge and had the highest strength of response. Similarly one of the lower quality teas (DM, Sample 9) conducted the least amount of current.

Sample Number

Grades

1 7/13 DM

2 BP

3 PF (highest quality)

4 D (lowest quality)

5 8/13 DM

6 BP

7 PF

8 D

9 10/13

DM

10 BP

Clustering of Samples relates the reliability of the results over a series of five trials

Different Manufacturing Dates may account for the varying results among the same tea sample Teas of lower quality (Sample 8, D) may have conducted more current than a traditionally higher quality tea due to it’s later

processing date

Teas processed earlier may have degraded over time

Less clustering in tea samples compared to basic taste inducing solutions because of higher

variability

Tea consists of numerous redox active polyphenols whereas the basic taste solutions were

composed of one compound

Other applications

Water quality analysis

Food contamination

Quantification of taste-masking ability different forms of oral medications such as capsules

and tablets

“Electronic Tongue” Mousumi Palit (2008).

“An electronic tongue based on voltammetry” Elsevir, Winquist et al. (357, 21 – 31) 1997

“Discrimination of tea by means of a voltammetric electronic tongue and different applied waveforms” Elsevier, Ivarsson et al. (76, 449 – 454) 2001.

Palit, M.; Tudu, B.; Dutta, P.K.; Dutta, A.; Jana, A.; Roy, J.K.; Bhattacharyya, N.; Bandyopadhyay, R.; Chatterjee, A., "Classification of Black Tea Taste and Correlation With Tea Taster's Mark Using Voltammetric Electronic Tongue," Instrumentation and Measurement, IEEE Transactions on , vol.59, no.8, pp.2230,2239, Aug. 2010

Tudu B, Jana A, Bandyopadhyay R. “Instrumental testing of tea by combining the responses of electronic nose and tongue” Elsevir vol 110. (356-363) 2012

http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0072592/