17-04-2014, 03:59 PM
Quantification of tastes of amino acids using taste sensors
[attachment=61550]
Introduction
Many foods contain amino acids, which are the fundamental
building blocks of proteins essential for maintaining the life func-
tions of humans. These essential amino acids must be obtained from
foods because they cannot be biosynthesized in the human body.
Among the essential amino acids, l-valine (l-Val), l-leucine (l-Leu),
and l-isoleucine (l-Ile) are branched-chain amino acids (BCAAs)
and account for approximately 35% of the total amount of essential
amino acids in body proteins [1]. BCAAs have been used in a variety
of applications, for example, as ingredients of oral medicines for
patients with hepatic cirrhosis and hepatic encephalopathy, who
have abnormalities in protein or amino acid metabolism, and as
supplements in sports drinks that can help prevent muscle fatigue
and assist recovery from fatigue [1–3].
Experimental
Taste sensing system
A taste sensing system (TS-5000Z, Intelligent Sensor Technol-
ogy, Inc., Japan) was used for the measurement of amino acids.
Each sensor has a working electrode with a lipid/polymer mem-
brane as the sensing part and a reference electrode. Changes in
the membrane potential generated when the working electrode is
immersed in each sample are measured. Fig. 1 shows schematic
diagrams of the working and reference electrodes. The working
electrode comprises a sensor probe, a lipid/polymer membrane,
a Ag/AgCl electrode, and an internal liquid (3.33 M KCl + saturated
AgCl). The reference electrode comprises a Ag/AgCl electrode and
an internal liquid (3.33 M KCl + saturated AgCl). A porous ceram-
ics is used for the liquid junction. Data on the membrane potential
obtained from both electrodes are sent to a computer.
Evaluation of bitterness suppression effect
To evaluate the bitterness suppression effect, the BCAAs l-Val,
l-Leu, and l-Ile were used as the bitter amino acid samples, and l-
Arg was used as the bitterness suppression substances. The sample
solutions used in the measurement were as follows: (1) 300 mM l-
Val, (2) 100 mM l-Leu, and (3) 200 mM l-Ile as single BCAA solutions
and (4) a mixed BCAA solution obtained by mixing 100 mM l-Val,
100 mM l-Leu, and 100 mM l-Ile solutions. The concentrations of
added l-Arg were 0.1–10 mM for the single BCAA solutions and
0.3–30 mM for the mixed BCAA solution. Each sample solution was
obtained by adding a sample to 1 mM KCl solution as a solvent.
All the reagents used as samples were purchased from Wako Pure
Chemical Industries, Ltd., Japan.
CONCLUSION
In this study, we proposed a method of quantifying the tastes
of amino acids using taste sensors that can selectively evalu-
ate the basic tastes, and demonstrated the bitterness suppression
effect. The bitter and sweet tastes of amino acids were selec-
tively evaluated using a negatively charged and highly hydrophobic
lipid/polymer membrane and a positively charged lipid/polymer
membrane, respectively. The bitterness and sweetness of amino
acids were evaluated successfully using the bitterness and sweet-
ness sensors, respectively. When simple linear regression analysis
was carried out on the response values obtained from the sensors
and the sensory scores for each amino acid sample, a strong corre-
lation was observed, indicating that the tastes of amino acids with
bitter, sweet, and complex (bitter and sweet) tastes can be esti-
mated. Moreover, the effect of l-Arg on suppressing bitterness was
demonstrated using the bitterness sensor that we developed.
These results reveal that the taste sensors utilizing
lipid/polymer membranes can quantify the taste of amino
acids contained in oral medicines and supplements. Such sensors
are expected to contribute to improving the taste of foods and
medicines containing amino acids.
[attachment=61550]
Introduction
Many foods contain amino acids, which are the fundamental
building blocks of proteins essential for maintaining the life func-
tions of humans. These essential amino acids must be obtained from
foods because they cannot be biosynthesized in the human body.
Among the essential amino acids, l-valine (l-Val), l-leucine (l-Leu),
and l-isoleucine (l-Ile) are branched-chain amino acids (BCAAs)
and account for approximately 35% of the total amount of essential
amino acids in body proteins [1]. BCAAs have been used in a variety
of applications, for example, as ingredients of oral medicines for
patients with hepatic cirrhosis and hepatic encephalopathy, who
have abnormalities in protein or amino acid metabolism, and as
supplements in sports drinks that can help prevent muscle fatigue
and assist recovery from fatigue [1–3].
Experimental
Taste sensing system
A taste sensing system (TS-5000Z, Intelligent Sensor Technol-
ogy, Inc., Japan) was used for the measurement of amino acids.
Each sensor has a working electrode with a lipid/polymer mem-
brane as the sensing part and a reference electrode. Changes in
the membrane potential generated when the working electrode is
immersed in each sample are measured. Fig. 1 shows schematic
diagrams of the working and reference electrodes. The working
electrode comprises a sensor probe, a lipid/polymer membrane,
a Ag/AgCl electrode, and an internal liquid (3.33 M KCl + saturated
AgCl). The reference electrode comprises a Ag/AgCl electrode and
an internal liquid (3.33 M KCl + saturated AgCl). A porous ceram-
ics is used for the liquid junction. Data on the membrane potential
obtained from both electrodes are sent to a computer.
Evaluation of bitterness suppression effect
To evaluate the bitterness suppression effect, the BCAAs l-Val,
l-Leu, and l-Ile were used as the bitter amino acid samples, and l-
Arg was used as the bitterness suppression substances. The sample
solutions used in the measurement were as follows: (1) 300 mM l-
Val, (2) 100 mM l-Leu, and (3) 200 mM l-Ile as single BCAA solutions
and (4) a mixed BCAA solution obtained by mixing 100 mM l-Val,
100 mM l-Leu, and 100 mM l-Ile solutions. The concentrations of
added l-Arg were 0.1–10 mM for the single BCAA solutions and
0.3–30 mM for the mixed BCAA solution. Each sample solution was
obtained by adding a sample to 1 mM KCl solution as a solvent.
All the reagents used as samples were purchased from Wako Pure
Chemical Industries, Ltd., Japan.
CONCLUSION
In this study, we proposed a method of quantifying the tastes
of amino acids using taste sensors that can selectively evalu-
ate the basic tastes, and demonstrated the bitterness suppression
effect. The bitter and sweet tastes of amino acids were selec-
tively evaluated using a negatively charged and highly hydrophobic
lipid/polymer membrane and a positively charged lipid/polymer
membrane, respectively. The bitterness and sweetness of amino
acids were evaluated successfully using the bitterness and sweet-
ness sensors, respectively. When simple linear regression analysis
was carried out on the response values obtained from the sensors
and the sensory scores for each amino acid sample, a strong corre-
lation was observed, indicating that the tastes of amino acids with
bitter, sweet, and complex (bitter and sweet) tastes can be esti-
mated. Moreover, the effect of l-Arg on suppressing bitterness was
demonstrated using the bitterness sensor that we developed.
These results reveal that the taste sensors utilizing
lipid/polymer membranes can quantify the taste of amino
acids contained in oral medicines and supplements. Such sensors
are expected to contribute to improving the taste of foods and
medicines containing amino acids.