YSM Issue 93.4 Full Magazine

FOCUS
Culinary Science
T H E SECRET
O F
SALTED CARAMEL
SODIUM CHLORIDE INTENSIFIES NEURAL FIRING IN RESPONSE
TO GLUCOSE BY ELISA HOWARD | ART BY MAYA GERADI
Imagine the luxurious taste of salted
caramel trickling over an ice cream
sundae, oozing out of a chocolate
candy bar, or glazing popcorn with a
shiny surface of delectable perfection.
In 1977, French chocolatier Henri Le
Roux struck the perfect balance between
sweet and salty in the development of
the amber-colored confection exploding
in popularity across the United States.
But, have you ever wondered why salted
caramel is such a heavenly treat for the
taste buds? Researchers in Japan found
the answer by investigating proteins
found in the kidneys and small intestine.
Taste buds located in papillae—
tiny bumps on the surface of the
tongue—house receptor cells that
generate electrical signals known as
action potentials in response to sweet,
salty, sour, umami, and bitter food
molecules. Fiber bundles known as
IMAGE COURTESY OF WIKIMEDIA COMMONS
The Mallory’s trichrome stain shows the taste buds
of mice viewed through optical microscopy.
the chorda tympani and
glossopharyngeal nerves
relay action potentials to the
nucleus of the solitary tract
for subsequent transmission to
the cortex. A group of proteins
classified as T1R receptors is
responsible for detecting artificial
sweeteners or natural sugars like glucose
and sucrose. However, in 2003, a study
led by Sami Damak found that mice
deprived of T1R3s maintained sugardetecting
abilities, thereby suggesting
alternate pathways for the perception of
sweet compounds.
Following this discovery, a team of
Japanese and American researchers
turned their attention to sodiumglucose
cotransporters (SGLTs),
protein molecules commonly found in
nephrons and small intestine mucosa.
SGLTs couple the favorable movement
of sodium ions with the uptake of
glucose molecules into the intracellular
space. All the while, sodiumpotassium
pumps maintain proper ion
concentrations inside and outside the
cell. Interestingly, the SGLT1 proteins
were recently discovered in the inner
lining of the mouth. To investigate
the role of these proteins in sugarresponsive
taste cells, professor Keiko
Yasumatsu of Tokyo Dental Junior
College and colleagues recorded the
neural activity in the chorda tympani
and glossopharyngeal nerves of eight to
twenty-week old laboratory mice. The
researchers prepared glucose and
sucrose solutions mixed with sodium
chloride (NaCl), a chemical commonly
known as table salt. The mice were
knocked unconscious through
anesthetic injections, and the solutions
were applied on their tongues. Then,
the mice were treated with phlorizin,
a glucoside acting as a competitive
inhibitor of SGLTs.
The researchers found that the chorda
tympani and glossopharyngeal nerves
of the mice fired more frequently in
response to glucose-NaCl solutions
than pure sugar solutions. All the while,
mixtures of table salt and artificial
sweeteners, citric acid, quinine, or other
taste compounds failed to generate
such enhanced activity. Indeed, the
combination of glucose and table salt
plays a decisive role in sweet taste
detection, as the SGLT1 receptors utilize
two sodium ions for the transport of
one glucose molecule into taste cells.
“In the presence of sugar molecules, the
increase in NaCl content of saliva allows
for the increased generation of action
28 Yale Scientific Magazine December 2020 www.yalescientific.org