1. Out of the sensory
box:
exploring the physics
of mouthfeel
George van Aken
info@insightfoodinside.com
george.vanaken@nizo.com
Jennifer Aniston (W Magazine photo shoot)
- 40% NIZO food research
- 60% independent scientist:
insight Food inside

2. 2Together to the next level
GUIDED TOUR IN
THE PHYSICS OF
MOUTHFEEL

3. Back to the basics
3
Food
structure and
composition
Interaction with
the body:
• Receptors
• Oral processing
• Digestion
Consumer
experience
• Sensory
perception
• Appetite and
Satiety
• Liking
Which adaptations needed?

4. After taste
oral and
pharyngeal coating,
flavour release
Masticatory
oral processing
structural changes,
flavour release
bolus formation
Subsequent perceptive stages
First bite
rheology, temperature
Appearance
color, shine,
structure, flow, smell
swallow
Neural and
hormonal
Feed back
Digestion, absorption,
glucose homeostasis, …
Hedonic response,
Wanting, Remembrance
satiety,
satisfaction,
craving
sensory
perception
cephalic
response

5. For example, ice cream goes from
thick to creamy to liquid before
swallowed
0 = start
1 = finish/swallow
Sequential perception as measured by
Temporal Dominance of Sensations (TDS)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
t (s)
%attributeselections
normalised TDS: 2 LF
Firmness
Melted
Sandiness
Slippery
Spreadability
%attributeselections
t (normalized)
Thick Creamy Liquid
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Task: Choose which attribute is currently
dominant:
creamy
thick
sweet
smooth
liquid
Acknowledgement
Harold Bult

6. In silico digestive physiology
modelling
• Timing of meals and drinks
• Speed of consumption
• Proteins, sugar, fat, water, pH
• Other compounds together or
separate from meal
Input parameters:
diet timing and
properties
Output:
temporal
variations
• Gastric pressure
• Gastric pH
• Gastric emptying
• CCK, PYY, GLP-1, GIP
• Digestive enzyme activity
• Bile secretion
• Small intestinal pH
• Absorption
• GI transit
• Insulin
Hunger, fullness,
bloating, satiety,
reward
Timed release
Bioavailability
Blood glucose
Physiology
literature
In vitro
measurements
Physiological variations
(infants, elderly, diseased)

7. MOUTHFEEL
What do we sense?
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8. What produces the forces sensed
by the tongue?
Viscous forces of the fluid
Friction of tongue and palate in
contact
Particles grinding between
tongue and palate
palate
tongue
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9. Similar textural sensory attributes for
skin and mouth
• Thick, viscous
• Stiff, gelled
• Elastic
• Firm, hard
• Crumbly
• Stringy
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• Rough
• Smooth
• Slippery
• Non-slipping
• Velvety
• Fatty
• Tough
• Short, long
• Shear thinning
• Thixotropic
• Melting
• Gritty(grainy)
• Sticky
• Soft
• Hard
• Sandpaper
Rheometers Tribometers

10. HOW ARE THE FORCES
SENSED?

11. M. Trulsson, G.K. Essick, J. Neurophys. 1997(77), 737-748
Tongue mechanoreceptors
Rapidly Adapting receptors:
sensitive to force variations
• Lower stress threshold of about 12 Pa
• Average stress threshold of about 60 Pa
• Rheology: vibrations caused by fracturing
• Tribology: vibrations caused by tumbling
particles, surface roughness
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Slowly Adapting receptors:
sensitive to constant forces
• Rheology: bulk viscous forces
• Tribology: static surface friction
forces

12. BOUNDARY AND
HYDRODYNAMIC FRICTION
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13. Transition to hydrodynamic lubrication
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14. Optical Tribological Configuration
14
Object on moving plate

15. Papilla roughness and deformability
Variation of normal stress (piglet tongue, OTC)
Frame size:
75 mm * 125 mm
Filiform
papilla
Glass
slide
Papilla surface
roughness ~ 20 μm
--
0 kPa 4.7 kPa 6.7 kPa
9.5 kPa 15 kPa 20.6 kPa

16. Generation of asymmetry in deformable
symmetrical bodies by hydrodynamic forces
No net lift force
undeformable
“steel window wiper”
velocity
Net lift force
deformable
“rubber window wiper”
velocity
Van Aken, G.A., Modelling texture perception by soft epithelial surfaces,
Soft Matter, 2010, 6, 826–834
Shear force Shear force
Lift
force

17. Tribological regimes (Stribeck curve)
Static friction
speed  viscosity
normal force
Friction force
hydrodynamic
boundary
mixed
Only viscous
forces
Static surface bonds
Transient surface bonds
and corrugations
Liquid starts to
interpenetrate
palate
papilla
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Smaller particles
can slip through
Gap-width
increases with
viscosity 

18. Together to the next level
Fluidic food bolus
gapwidth

19. Example: for emulsions Thickness
and Creaminess are not the same:
creaminess correlates to thickness only in the
presence of emulsified fat
The difference is related to
the presence of a fatty
coating on the oral
surfaces: barrier & lubricant
Higher viscosity from:
• More emulsified fat
• More thickener, starch,
protein
• More droplet aggregation
Higher viscosity from:
• More thickener, starch,
protein

20. The oral environment:
restructuring effects
• Temperature
• Melting of solid fats (chocolate)
• Melting of gelatin
• Shear
• Breakup of gels, mixing with saliva
• Produces a swallowable paste of smaller gel particles
• Rubbing between tongue and palate
• Reduces the viscosity: thixotropy of gels, shear thinning behaviour of thickened fluids
• Saliva
• Dilutes
> reduces viscosity-increase obtained from emulson droplets, particles and polymer thickened fluids
• Contains α-amylase which breaks down starch polysaccharides
> thinning of starch-based thickened fluids and gels
• Contains highly glycosylated HMW proteins (mucins)
> aggregation of microbes, particles > cleaning activity, viscosity increase
> bolus formation, viscous, semi solid, slippery to assist swallowing
> lubrication > mucins flocculate on acidification > loss of lubricating function
• Mucus coating on the eptithelial surfaces (tongue, gums, palate)
• Protective gel layer, provides lubrication
• Teeth
• Fracturing, deminution, reshaping gels into a bolus of a fluidic dispersion
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MUC5B; 10-40 MDa MUC7; 200 kDa

21. Interaction with the tongue
a thin coating of (emulsified) fat reduces boundary friction
Visualization of fat
retention on piglet tongue
Emulsion:
10 wt% SF oil; 1 wt% WPI
CSLM image (Nile blue staining)
500500 mm
red: oil; green: tongue papillae
Dresselhuis et al., Journal of Colloid and Interface Science (2008) 21
Human
tongue

22. Emulsion droplets increase
creamy mouthfeel because:
• As filler particles they increase the viscosity
• of saliva
• of viscous food media
• filler effect enhanced by aggregation/clumping
• As oil releaser help to reduce boundary friction
• Driven by coalescence with tong surface
• larger droplets
• more solid (saturated) fat by partial coalescence
• less stable droplet interface (emulsifiers, lipids, proteins,
hydrophobised starch)
• For cheese
• Fat helps to break up and hydrate the casein
matrix into a viscous paste
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Tongue
scraping
Saliva
Guar
Couva 760P
OSA

23. 23
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Low-fat hard cheese
Slowly
hydrating
dense cheese
particles
Thin dilute
emulsion of
small droplets
23
Normal hard cheese
Forgeable particles,
quickly hydrating
Viscous
concentrated
emulsion of
aggregated
droplets
Solids: breakdown path of
fracturing and dissolution important
separation

24. ACOUSTIC TRIBOLOGY
Direct in-mouth measurement of boundary friction
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25. New measuring technique:
Acoustic tribology
van Aken, Food Hydrocolloids, 31 (2013), 325-331
25
In vivo measurement of sound emission due to tongue friction/roughness.
New variant
allows
external
measurement
"Sandpaper Ballet"
Leroy Anderson (1954)

26. Acoustic tribology: the principle
26
Microphone line voltage
during rubbing of the tongue;
sequence of products
spectrum analysis, selected
frequency range
saliva creamer honeymargarine vinegar peanut
butter
spectrum analysis
Acoustic signal or
tongue roughtness
• Decreases with the viscosity
of the tongue coating
• Increases with
acidity/astringency

27. Examples
Black coffee – white coffee
Water - banana
Water - white coffee

28. Acoustic tribology:
variation in fat content in dairy products
In vivo acoustic measurement of tongue roughness, which is
directly related to creaminess and astrigency, showing that
the effect of fat content differs with dairy product type.
28
lesscreamy
0
0,0001
0,0002
0,0003
0,0004
0,0005
0,0006
0,0007
0,0008
0,01 0,1 1 10 100
integratedacousticsignal(a.u.)
fat content (weight %)
Milk
Yoghurt
Cheese T/P
Cheese T/C
Quark

29. Effect of half-fat creamer on coffee
0
0,0001
0,0002
0,0003
0,0004
0,0005
0,0006
0,0007
1
saliva
coffee black
coffee with creamer
creamer
creamer later
Astringency of coffee: acidity and phenolic compound bind the
lubricating salivary mucins,
Astringency
of coffee
Smoothening
by creamer

30. Kinetics
system: cream after saliva
Observed are the
effects of
inhomogeneous mixing
and finally a
replacement of native
mucosal layer by a
lubricating fat layer0,0E+00
2,0E-05
4,0E-05
6,0E-05
8,0E-05
1,0E-04
1,2E-04
1,4E-04
integratedacousticsgnal(a.u.)
saliva
cream 2 s
cream 2,3 s
cream 2,7 s
cream 2,9 s
cream 3,1 s
time

31. Electret tongue rubbing
Sensitive to tooth plaque and pellicle
31
recorder
• Low-frequency sound enhanced when saliva is replaced by both types
of fruits (banana, orange)
• High-frequency sound strongly increased for banana compared to saliva
and orange
Tongue tip rubbed horizontally
(left to right) against back of
upper incisors.
saliva
orange banana

32. recorder
Electret tooth tapping sounds
32
Tapping of teeth:
• Banana produces a pellicle that
dampens high frequencies
• Orange removes this banana pellicle
Tapping of teeth before and
after removal of plaque by
tooth brushing:
• Bacterial plaque dampens the high
frequency sounds
>100x at 10 kHz
orange
banana
CLEAN
PLAQUE
Molars
Incisors
Molars
Incisors
Incisors

33. CRISPY AND CRUNCHY
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Texture
technologies
Texture
technologies

34. Chocolate rice cracker
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Smaller bits quickly get softened by saliva
 fractering sound disappears
Single bite:
about 10 chews

35. Comparison between crispy
and/or crunchy food products
• Fresh from the pack
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36. First bites
Loudest of first 3 bites
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• Crispness relates to high amplitudes in frequencies
2-10 kHz; highest for Pringles, lowest for Brioche
• Snap relates to a peak around 1 khz and a relative
strong decay to higher frequencies; highest for carrot and
freshly roasted Pecan nut; Buggles and Wokkels also shows snapping features

37. Duration of sound from the first bite
loudest of first 3 bites
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Fracture propagates laterally through a thin sheet
Teeth squash through a thick layer of material

38. Cruchiness
• Extented sequence of sound generating
chews ( > 3 kHz)
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Pringles
Dorito’s
Nibbits
Lay’s natural
“typewriter song”
Leroy Anderson (1950)
Henri Matisse (1910)

39. Stailing
• Loss of crispy chrunchy behaviour in the open
air: first bites 0, 1 and 5 h
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40. Mixed chewing and rubbing
Chewing a cashew nut and intermittent tongue rubbing
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chewing
rubbing 0 rubbing 1 rubbing 2 rubbing 3 rubbing 4
chewing chewing chewing
native
large
particles
formed
• Large particles disappear
from oral coating
• Lubrication increases
(fat, viscous bolus?)
Particles
Lubrication
by fat

41. Panel versus Acoustic
- Quantitatively measurable in 1
subject
- Fast, high time resolution
- Directly related to oral food
behaviour
- Not affected by other sensory
cues
- Differences between subjects
measurable
- Limited to tactile cues
- Labour intensive panel
- Consensus on sensory
descriptors needed
- Repeatabiliy among panels
often limited
- Aroma/tastant/tactile cues
affect each others
- Statistics
- No direct relation with the
physics involved
- Sensory stimuli vary before,
during and after oral presence

42. Understanding and control of oral
processing has greatly supported
product development
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43. 43Together to the next level
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Creating the future together
www.nizo.com
george.vanaken@nizo.com
www.insightfoodinside.com
info@insightfoodinside.com