Embed Size (px)
Citation preview
1
Identifying the Taste of Fat
David W. Pittman, Ph.D.Department of Psychology
Wofford College
Does fat have a taste?
• Why do we prefer to eat fatty foods?
• Is there a difference between fat-free and regular fat food products?
• Common experience suggests that there is a taste component to fat.
• Fat has been relegated to a role in texture perception rather than taste.
Brief Background on the Taste (Gustatory) System
• Four generally accepted classifications of taste stimuli: SWEET, SOUR, SALT, BITTER– UMAMI– monosodium glutamate
• Based on the ability of chemicals to activate neural signals in particular gustatory nerves
• Temperature (thermal or chemical: capsaicin), texture, viscosity, etc. are considered general sensory properties
Stimulus Interaction with Taste Receptor Cells
• Enzymes in saliva break down food into dissolved chemicals in the oral cavity
• Chemicals interact w/ taste receptor cells
• Neural signal sent to the brain
Chemical Transduction
Taste Cell
DEPOLARIZATION (+) equals neural signal to the brain
Neural Signaling & Areas of the Central Nervous System
• 3 taste nerves converge in the brainstem
• Insula = quality of taste
• Areas for other sensations related to taste such as hunger, pleasure, and aversive
2
Does fat have a taste and not just a texture component?
• Jim Smith at Florida State University
• Can rats discriminate between corn oil and mineral oil?– Similar texture– Different chemical
composition
Rats can detect a difference between
corn oil & mineral oilData from: Smith JC, Fisher EM, Maleszewski V, McClain B. Orosensory factors in the ingestion of corn oil/sucrose mixtures by the rat. Physiol Behav . 2000 Apr 1-15;69(1 -2):135 -46.
What chemicals in corn oil could be taste stimuli?
• Fat is composed of combinations of fatty acids• When fat is broken down *enzymes in saliva*
these free fatty acids become available for chemical stimulation.
• What is the free fatty acid composition of corn oil?
15231313Corn Oil
LinolenicLinoleicOleicStearicPalmitic
Can rats detect linoleic acid?
Conditioned Taste AversionA simple paradigm for powerful results!
NaCl
LiCl
Measure the Taste Aversion with a 2-bottle preference test
<50% = avoidance of LA compared to H2O>50% = preference of LA compared to H2O
• Measure intake by difference in bottle weight
• Preference score = LA / (LA + H2O)
• 50% = equalconsumption
Detection of Linoleic Acid
44 66 88Linoleic Acid Concentration (micromolar)
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Pre
fere
nce
Sco
re
LiClNaCl
Detection of Linoleic Acid
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
44 66 88Linoleic Acid Concentration (micromolar)
Pre
fere
nce
Sco
re
LiClNaCl
3
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
44 66 88Linoleic Acid Concentration (micromolar)
Pre
fere
nce
Sco
re
LiClNaCl
Detection of Linoleic Acid
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
44 66 88Linoleic Acid Concentration (micromolar)
Pre
fere
nce
Sco
re
LiClNaCl
* *
Detection of Linoleic Acid
To Summarize Experiment 1:
• Rats can detect Linoleic Acid!• The threshold for detection is between 44 & 66
micromolar concentration (14 ul / 1 liter)• Small concentration similar to the amount
that could be produced by saliva enzymes!
Gustatory Neural Pathways
• CT = anterior 2/3 tongue
• GL = posterior 1/3 tongue
• GSP = palate• Converge in the
NST to CNS taste areas
The Role of the Chorda Tympani Nerve
• 88 µM Linoleic Acid conditioned taste aversive test• ShamCTX = surgery to expose but not cut the CT• CTX = bilaterally cut CT – eliminates taste neural
signals from anterior 2/3 of tongue
• CTX shows an aversive then GL or GSP nerves transmit gustatory signals for detection of Linoleic Acid
• CTX does not show an aversive then the chorda tympani transmits necessary gustatory signals for detecton of Linoleic Acid
The Role of the CT Nerve
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
LiCl & CTX(n=10)
NaCl & CTX(n=5)
LiCl &ShamCTX
(n=5)
NaCl &ShamCTX
(n=5)
Pre
fere
nce
Sco
re
*
4
The Role of the CT Nerve
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
LiCl & CTX(n=10)
NaCl & CTX(n=5)
LiCl &ShamCTX
(n=5)
NaCl &ShamCTX
(n=5)
Pre
fere
nce
Sco
re
*
To Summarize Findings:
• Rats prefer fat (corn oil) similar to humans.• Rats detect & avoid very low concentrations of
Linoleic Acid, a free fatty acid component of corn oil.
• Rats without a chorda tympani nerve can not detect & avoid Linoleic Acid.
• Rats can taste Linoleic Acid and the signal is likely sent through the chorda tympani nerve!
Gilbertson recorded from taste receptor cells while applying free fatty acids.
Taste Cell
DEPOLARIZATION (+) equals neural signal to the brain
Linoleic Acid
Gilbertson’s Data
• Linoleic acid and other related free fatty acids inhibited the Shaker Kv1.5 channel
• Linoleic acid enhanced stimulus -induced depolarization of the taste receptor cell
Data from: Gilbertson TA, et al. Fatty acid modulation of K+ channels in taste receptor cells: gustatory cues for dietary fat. Am J Physiol. 1997 Apr;272(4 Pt 1):C1203-10.
What effect does Linoleic Acid have on other tastes in an intact animal model?
• Controlled presentation of up to 16 bottles
• Computer controls shutter access & counts licks
• The Davis Rig
0
20
40
60
80100
120
140
160
16 31 63 125 250Sucrose Concentration (mM)
Mea
n Li
cks
/ 20
s
Sucrose
Sucrose + 88 uM Linoleic
Effect of 88 µM Linoleic Acid on Sweet Taste
5
Effect of 88 µM Linoleic Acid on Sweet Taste
0
20
40
60
80100
120
140
160
16 31 63 125 250Sucrose Concentration (mM)
Mea
n Li
cks
/ 20
s
Sucrose
Sucrose + 88 uM Linoleic
0
0.2
0.4
0.6
0.8
1
1.2
1.4
31 63 125 250 500 1000NaCl Concentration (mM)
Tas
tant
/ W
ater
Rat
io
NaCl
NaCl + 88 uM LinoleicAcid
Effect of 88 µM Linoleic Acid on Salt Taste
Effect of 88 µM Linoleic Acid on Salt Taste
0
0.2
0.4
0.6
0.8
1
1.2
1.4
31 63 125 250 500 1000NaCl Concentration (mM)
Tas
tant
/ W
ater
Rat
io
NaCl
NaCl + 88 uM LinoleicAcid
0
0.2
0.4
0.6
0.8
1
1.2
1.4
2 4 8 15 30 60Citric Acid Concentration (mM)
Tas
tant
/ W
ater
Rat
ioCitric Acid
Citric Acid + 88 uM LinoleicAcid
Effect of 88 µM Linoleic Acid on Sour Taste
Effect of 88 µM Linoleic Acid on Sour Taste
0
0.2
0.4
0.6
0.8
1
1.2
1.4
2 4 8 15 30 60Citric Acid Concentration (mM)
Tas
tant
/ W
ater
Rat
io
Citric Acid
Citric Acid + 88 uM LinoleicAcid
Effect of 88 µM Linoleic Acid on Bitter Taste
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1 2 4 8 15 30
Quinine-HCl Concentration (mM)
Tas
tant
/ W
ater
Rat
io
QHCl
QHCl + 88 uM LinoleicAcid
6
To summarize the Davis Rig experiment results:
• Linoleic Acid increased intake of preferable solutions: Sweet / Sucrose
• Linoleic Acid decreased intake of unpleasant solutions: Salt / NaCl & Sour / Citric Acid
• Supported Gilbertson’s theory that Linoleic Acid inhibition of the K+ channels would increase the intensity of taste stimuli
The Taste of Fat• Fat acts on the taste system through its free
fatty acid components.• Linoleic Acid by itself can be detected by rats.• When mixed with other tastes, Linoleic Acid
acts to increase the intensity of taste in rats.
Future Directions:• Identifying the detection abilities of rats for other
free fatty acids such as palmitic and oleic acid• Identifying the neural coding for the detection of
linoleic acid in the chorda tympani nerve• Increasing the concentration of linoleic acid or
using other free fatty acids with tastant intake• Appling this rodent model to human
detection and perception of free fatty acidsThis presentation & more information available at:
http://FatTaste.OnTheWeb.nu
Acknowledgements:FUNDING:
Independent Colleges & Universities of South Carolina (ICUSC)
Committee on Non-Curricular ConcernsDr. Dan Maultsby, Dean of the College
This presentation & more information available at:
http://FatTaste.OnTheWeb.nu
Acknowledgements:STUDENTS:
Research Assistants: Danielle McCormack and Petra Herzog
Krysta WebsterFall 2003 Senior Thesis Group:
Sallie Cheek, Steven Robinson, & Dylan Scott
This presentation & more information available at:
http://FatTaste.OnTheWeb.nu
Free Fatty Acids: the Taste of Fat
