This presentation discusses the structural changes that occur during oral processing, and how these determine sensory perception. Tactile perception is discussed theoretically on the basis of the forces exerted onto the tongue surface and the sensitivity of mechanoreceptors. Specific attention is given to the state of lubrication of the tongue surface, introducing a new acoustic real-time in vivo measering technique for the state of lubrication of the human tongue surface.

1. Sensory
Management Jennifer Aniston (W Magazine photo shoot )
George van Aken
george.vanaken@nizo.nl
EFFoST, September 2011, Berlin
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2. Introducing NIZO food research Processing centre
Application centre
• Independent, private contract
HQ - Ede, The Netherlands
research company for the food
industry
• Founded in 1948, now leading
European research company
• Roots in dairy industry
• Working with customers to
achieve their goals
• HQ in “Food Valley” in The
Netherlands Offices abroad:
• Offices in France - Mr. Damien Lemaire
UK - Dr. Jean Banks
France, UK, USA, Japan
USA / Canada - Dr. Ralf Jäger
• 200 professionals Japan - Dr. Maykel Verschueren
• State-of-the-art facilities & food-
grade processing centre
Research centre
• ISO 9001:2000 certified
Technology for your success
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3. Product groups
My main involvements
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4. Sensory management
Contents
• Why important?
• Sensory perception: multimodality and role of
oral processing
• Tactile perception
• (acoustic) tribology
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5. Why important?
TASTE: Motivation to buy
Source: the Henley Center
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6. Improves sensory
High caloric properties
(9 kcal /g versus 4 kcal/g
(aroma release, smooth
for sugar and protein,
plasticity, lubrication))
Often low satiation)
Metabolic One of the Creamy,
syndrome, Rich,
Obesity main
FAT Pleasure
directions
Texturizer Main
(thickeners, structure breaker,
air stabilizer, frying agent)
essential
ingredient
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7. Sensory research for dietary
products
• Dietary products
• Reduced fat, high fiber, low salt and sugar
• Enhanced satiety
• Nevertheless tasty
• Technology to produce such systems
• Stable textures
• Corrected microstructures
• Fat replacers, controlled flavour release
• Methods to quantify the sensory functionality
• Of the original product
• Of the healthier product
• Toward understanding and directing technology
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8. Sensory perception
MULTIMODALITY AND ORAL
PROCESSING
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9. Sensory response is multimodal
Perception
Senses
Vision
Touch
Sound
Mouthfeel
Taste
Smell
CCK, PYY,
Gastrin,
Nutritional Hedonic consumer
vagus nerve
status response
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10. Cross modal interactions:
Viscosity affects flavour intensity perception
Nose space Sensory intensity
5
4.5
concentration (au)
gel 1 4
gel 1 soft
sensory Intensity
Nose-space
gel 2 3.5 gel 2
gel 3 3 gel 3
gel 4 2.5 gel 4
gel 5 2 gel 5 hard
1.5
1
0.5
0
0 20 40 60 80 0 20 40 60 80
time (s)
time (s)
Texture-flavour interaction at perception level!
(K. Weel, A. Boelrijk et al., published 2002)
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11. Cross modal interactions:
Aroma affects texture perception
90
80
70
• Equal firmness for each
casein concentration
perceived firmness
60
50
• Aroma concentration
40
varied as
30
A<B<C
20
10
ABC ABC ABC
0
Increasing caseinpH
high concentration low pH
Casein gels with variation in butter flavor.
• Janine E. Knoop, 5th Conference on Consumer Sciences 2010, Bilbao Spain 06-09-10
• Janine E. Knoop, G. Sala, J.H.F. Bult, M. Stieger, G. Smit, “Texture modification by butter aroma in cheeses and dairy
model gels” Poster [P2.03] at the 7th NIZO Dairy Conference
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12. Role of oral processing
Sight visual ORAL PROCESSING
F
nasal retronasal
Smell L
A
Taste release V
O
Chemical release U
R
T
Touch tactile initial bite
E
X
mastication T
U
Hearing breakage R
E
First bite TIME Swallow
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13. Example of oral processing:
Large structural changes, even for thin liquid emulsions:
THIS is what you taste!
Study carried
out within
The emulsions team:
Diane Dresselhuis
Erika Silletti
Guido Sala
Els de Hoog
Monique Vingerhoeds
Jan Benjamins
Franklin Zoet
Jerry van Maanen
Eefjan Timmerman
George van Aken

14. Structural changes in the oral cavity
Food emulsions
Saliva-induced Formation of slimy
droplet aggregation structures
Droplet-coating of Inhomogeneous coverage
oral surfaces of tongue papillae
Amylase induced
Droplet coalescence starch breakdown
Fat spreading at air Droplet spreading at
bubble surfaces tongue surface
Fracture of gels into Release of
„crumbs‟ emulsions droplets
Van Aken et al., Food Colloids, Dickinson ed., RSC, 2005, pp.356 – 366;
Curr. Opin. Colloid Interface Sci. 2007, 12, 251-262. .

15. Viscosity (100 s–1) increases in the mouth due to
saliva-induced droplet aggregation
ξ<0 ξ>0
Liquid emulsion
Saliva-induced
droplet
aggregation
Vingerhoeds et al. Food Hydrocolloids, 23(3) (2009), 773-785.
Van Aken et al., Curr. Opin. Colloid Interface Sci. 12 (2007), 251-262.

16. In vitro masticated gels: effects of gel
type and fat content
Emulsified oil:
 = 0, 5, 10, 20 wt% oil
• Increases the viscosity of the 1.4
masticated bolus 1.2 WPI
(for gelatin unbound opposite)
1
Friction coefficeint
φ Carrageenan bound
• decreases the friction of the
0.8
masticated bolus Carrageenan unbound
0.6
(large effect)
φ
0.4 φ Gelatin bound
φ
0.2
Gelatin unbound
0
0 0.5 1 1.5 2
Viscosity (Pa s) at 100 s-1
MTM tribometer
Chojnicka et al., Food Hydrocolloids (2009), 23, 1038-1046
(rubber versus stainless steel)

17. Effect of fat on aroma release
Flavour release for low fat quark, full fat cream and vegetable cream in the presence (+) of Flavour release for low fat quark, full fat cream and vegetable cream in the presence (+)
dairy flavour dairy flavour
2.0E+05
1.2E+00
normalised intensity (a.u)
low fat Quark (+) 1.0E+00
low fat Q
full fat cream (+)
Intensity (a.u)
full fat c
8.0E-01
6.0E-01
4.0E-01
2.0E-01
~+50%
0.0E+00 0.0E+00
0 0.25 0.5 0.75 0 0.25 0.5 0.75
Time (min) Time (min)
Difference in intensity of Adjust aroma concentration Difference in duration of
aroma release release
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18. What makes emulsions creamy?
GEL FRACTURING dependent on gelling
agent and droplet interaction
ACTIVE saliva
VISCOUS
BOLUS of
gel particles Thick
INACTIVE and saliva
saliva
Gelled
emulsion
Rich
HIGHER VISCOSITY by saliva
–induced droplet flocculation rubbing,
EXTENDED
aroma release
Creamy
shear
saliva
Smooth
shear LUBRICATING
saliva FATTY COATING
Liquid Droplet coating
on oral surfaces Coating
emulsion
26 refereed journal publications and 8 book chapters (2005-2011) by the TIFN project team
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19. Message: sensory
perception of food
highly dependent of
oral processing
palate
mucins
Taste buds mechanoreceptors
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20. Instrumental toolbox at NIZO
Textural Compositional
( e.g. viscosity, elasticity, friction, ( e.g. oral food deposition, aroma release,
fracturing, microstructure) taste-receptors interaction)
hard, thick, full melting slippery fatty creamy
brittle, creamy palatable smooth sweet lingering
elastic satisfying chewable coating coating full of flavour
Native system Expectorate Adhered mucous Artificial Olfactometer
analysis analysis layer analysis throat PTR-MS
(rheology, tribology, (chemical, rheology, (chemical, tribology, (in vitro aroma (in vivo aroma
microscopy) tribology, microscopy) , microscopy) release) release)
Instrumental toolbox
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21. Toward understanding
TACTILE PERCEPTION BY THE
TONGUE
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22. What produces the forces sensed
by the tongue?
 Viscous forces of the fluid in palate
motion relative to the tongue
surface
tongue
 Friction of tongue and palate in
palate
contact
 Particles grinding between tongue
tongue and palate palate
tongue

23. Main regimes thickness perception
Curve from: Shama, F. and P. Sherman (1973). J. Texture Studies 4: 111-118.
Viscous
forces 104
Sensitivity RA
perceived receptors measured by
 Trullson and Essick
J. Neurophys. 1997(77), 737-748
103
shear stress (Pa)
102
Average stress
thresshold
101
Lower stress
thresshold
100 Thickness not necessarily
g&
100 101 102 103 104
shear rate (s-1 ) related to perceived
viscous forces
Van Aken, G.A., Modelling texture perception by soft epithelial surfaces, Soft Matter, 2010, 6, 826–834

24. Tongue surface
mechanoreceptors embedded in papilla filiformis
20 m Flaking cells on
Source: Freeman,, Bracegirdle ,
nd
An atlas of hystology 2 ed.
the palate
Heinemann Educational
20 m Papilla filiformis (rabbit)
Surface roughness
of about 20 m
Human filiform papillae

25. Tribological regimes (Stribeck curve)
Friction force
Hydrodynamic modelling
Static surface bonds
Static friction of the soft deformable
papilla surface*
Transient surface bonds and
corrugations
palate boundary Only viscous
forces
Liquid starts to
interpenetrate
hydrodynamic
papilla Gap-width
mixed
increases with
speed  viscosity
speed 
viscosity
* Van Aken, G.A., Modelling texture perception by soft epithelial surfaces, Soft Matter, 2010, 6, 826–834

26. Free flowing; Slowed free flow; Forced flow;
Boundary Viscous shear friction Thinning time
friction sensed too small; Boundary sensed; Viscous
friction only if tongue shear friction
is pressed sensed
“RAW TONGUE” “CREAMY LIQUID” “THICK”
minimum gap width (micrometers)
1000 Pn (Shama & Sherman)
100 Pa,  = 1
100 Pa,  = 0
100 140 Pa,  = 0
Papilla surface
Molten chocolate
roughness
Stirred yoghurt
Skimmed milk
10
Vegetable oil
Whole milk
Cream
Honey
1
1 10 100 1000 10000
Interaction with saliva viscosity (mPas)

27. Tactile perception of a fluidic food bolus
gap width
Smooth
tongue
Sandpaper
tongue
high fat

28. Solids: breakdown path of
fracturing an dissolution important
Viscous
emulsion of
Normal hard cheese coalesced
droplets
Forgeable particles,
quickly hydrating
28
Slowly
hydrating
dense cheese
particles
Light hard cheese separation
Thin dilute
emulsion of
small droplets
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29. Solids: hard cheese as example Low-fat cheese
Mastication pathway (caricature)
Full-fat
particle size
gap width ~
detectable
cheese

30. Experimental evaluation of tongue roughness
TRIBOLOGY
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31. How to measure friction?
• Tribometry
• Measures the lubricating effect of food materials on
artificial surfaces
• Low frequency
• In vitro, independent of individuals
• Reproducible, established
• Acoustic measurement (NEW)
• Measures the sound generated by scraping surfaces
• High frequency (more similar to the sensitivity of the
tongue mechanoreceptors)
• In vivo, in mouth
• Includes the effects of the interaction between food and the
mucosa (e.g. acidic and astringent food)
• Includes the effect of oral processing
• Includes the effects of pre-meals and individual differences
•
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32. Liquid and soft semi solids:
tribological studies
Silicon Rubber Load: 5N Temp.: 21°C
0.6
0.5 - Which speed? ?
water
skim milk
Traction Coefficient (-)
whole milk MTM tribometer
yoghurt 3% fat
0.4
- Which load? yoghurt 0% fat
0.3 - What about the interaction with saliva?
yoghurt 3% fat
- What about the actual oral surfaces?
quark 0% fat
0.2
- Papillae quark 10% fat
0.1
- Mucous epithelial layer
0.0 - Variability (individuals, pre-meals, …)
5 10 100 800
Speed (mm/s)

33. Mouth-mimicking friction measurement
Pig tongue
Fat content
In-mouth friction
Optical Tribological Tongue roughness
Configuration (OTC)
Creaminess
Diane Dresselhuis

34. (NEW) Analysis of the in vivo
scraping sound of the tongue
• For a good analysis, many additional sounds must be removed
(breathing, clicks, air flow by tongue manipulations)
• Most relevant seems to be the frequency ranges 100-1000 Hz and 4-12 kHz
1,E+00
water coffee with cream water (saliva)
1,E-01
coffee with (whipping) cream Log scale!
1,E-02
Effect is a
factor 10
amplitude (V)
1,E-03
(1 order of
1,E-04 magnitude)
1,E-05
1,E-06
Line voltage as a function of time 1,E-07
1 10 100 1000 10000 100000
frequency (Hz)
Corresponding frequency spectrum of
the cleaned signal
Example: Water - coffee with (whipping) cream

35. WATER-SKIMMED MILK-FULL MILK-CREAM
milk range milk range, standardized on water
3,5
1,E-02
skim milk
water 3
full fat milk
skim milk
1,E-03
full fat milk 2,5 cream
cream
Amplitude (V)
Amplitude (V)
1,E-04 2
1,5
1,E-05
1
1,E-06 water
0,5
1,E-07 0
1 10 100 1000 10000 100000 1 10 100 1000 10000 100000
Frequency (Hz) Frequency (Hz)
Interpretation:
• tongue friction increases by protein (not observed by conventional
tribology), but is reduced in the presence of emulsified fat
• translates to: skimmed milk more rough/dry/astringent than water, but
milk fat makes it more smooth
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36. Effect of half-fat creamer on coffee
1,E-01 45
40
1,E-02
35 saliva/background
background
saliva 30 black coffee/background
1,E-03 coffee black
Amplitude (V)
Amplitude (V)
coffee with creamer 25 coffee with
creamer/background
creamer
20 creamer/background
1,E-04 creamer later
15
creamer later/background
10
1,E-05
5
1,E-06 0
1 10 100 1000 10000 100000 1 10 100 1000 10000 100000
Frequency (Hz) Frequency (Hz)
Although the spectra are rather noisy, a clear trend is observed:
• Coffee black
• Coffee with creamer Less friction sound
• Saliva
• Pure creamer
Later use of creamer again leads to a slightly larger signal. This may be
because the grinding with black coffee had temporarily smoothened the
tongue surface.

37. Kinetics
system: clean mouth with saliva
1.E-01
No clear time
1.E-02
saliva 1st second
dependence is
saliva 1,5-2 s
saliva 3-3,5 s
observed for
1.E-03
saliva.
amplitude (V)
saliva 4,3-4,7 s
1.E-04
1.E-05
1.E-06
1.E-07
10 100 1000 10000 100000
frequency (Hz)

38. Kinetics
system: half-fat coffee creamer
1.E-01
2s
Observed is a gradual
1.E-02 2,3
s
decrease in sound
2,7
s
amplitude
1.E-03
2,9
amplitude (V)
s
1.E-04
3,1
s
This suggests that at
the tongue surface, the
1.E-05
native mucosal layer is
1.E-06
slowly replaced by the
ingredients of coffee
1.E-07 creamer (fat, proteins?)
10 100 1000 10000 100000
frequency (Hz)

39. Kinetics
sequence of systems in one run:
half fat creamer – non carbonized soft drink – half fat creamer
Frequency spectrum slightly smoothed
Clearly, the acidic soft
drink gives a higher
signal than the half fat
creamer.
The signal of the half
fat creamer is lower if
it is preceded by the
acidic soft drink.
Possibly the grinding
of the acidic soft drink
smoothens the tongue
surface

40. Applications acoustic tribology
• Measurement tool for rough/dry mouthfeel (“sandpaper tongue”)
o Low fat products
o Astrigent products
o High protein products
• Measurement tool for surface textures
o Fabrics, wood, etc.
o Good-grip surfaces
• Measurement tool hair care/skin care application
(smoothness, silkiness)
• Measurement tool for other applications (ball
bearings, abbrasion, etc.)

41. Creating the future together
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