out of the sensory box final

Out of the sensory

box:

exploring the physics

of mouthfeel

George van Aken

[email protected]

[email protected]

Jennifer Aniston (W Magazine photo shoot)

- 40% NIZO food research

- 60% independent scientist:

insight Food inside

2Together to the next level

GUIDED TOUR IN

THE PHYSICS OF

MOUTHFEEL

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?

After taste oral and

pharyngeal coating,

flavour release

Masticatoryoral processing

structural changes,

flavour release

bolus formation

Subsequent perceptive stages

First bite rheology, temperature

Appearancecolor, 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

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 10

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

t (s)

% a

ttri

bute

sele

ctions

normalised TDS: 2 LF

Firmness

Melted

Sandiness

Slippery

Spreadability

% a

ttri

bu

tesele

cti

on

s

t (normalized)

Thick Creamy Liquid

Together to the next level

Task: Choose which attribute is currently

dominant:creamy

thick

sweet

smooth

liquid

Acknowledgement

Harold Bult

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)

MOUTHFEELWhat do we sense?


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


Similar textural sensory attributes for

skin and mouth

• Thick, viscous• Stiff, gelled• Elastic• Firm, hard

• Crumbly• Stringy


• Rough• Smooth• Slippery• Non-slipping

• Velvety• Fatty

• Tough• Short, long• Shear thinning• Thixotropic

• Melting

• Gritty(grainy)• Sticky• Soft• Hard

• Sandpaper

Rheometers Tribometers

HOW ARE THE FORCES

SENSED?

10

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 roughness11Together to the next level

Slowly Adapting receptors:

sensitive to constant forces

• Rheology: bulk viscous forces

• Tribology: static surface friction

forces

BOUNDARY AND

HYDRODYNAMIC FRICTION


Transition to hydrodynamic lubrication


Optical Tribological Configuration

14

Object on moving plate

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

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 forceLift

force

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


Smaller particles

can slip through

Gap-width

increases with

viscosity


Fluidic food bolus

ga

p w

idth

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

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


MUC5B; 10-40 MDa MUC7; 200 kDa

Interaction with the tonguea 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)

500500 mm

red: oil; green: tongue papillae

Dresselhuis et al., Journal of Colloid and Interface Science (2008)21

Human

tongue

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 22Together to the next level

Tongue

scraping

Saliva

Guar

Couva 760P

OSA


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

ACOUSTIC TRIBOLOGYDirect in-mouth measurement of boundary friction


New measuring technique:

Acoustic tribologyvan 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)

Acoustic tribology: the principle

26

Microphone line voltage

during rubbing of the tongue;

sequence of products

spectrum analysis, selectedfrequency 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

Examples

Black coffee – white coffee

Water - banana

Water - white coffee

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

less

cre

am

y

0

0,0001

0,0002

0,0003

0,0004

0,0005

0,0006

0,0007

0,0008

0,01 0,1 1 10 100

inte

grat

ed

aco

ust

ic s

ign

al (

a.u

.)

fat content (weight %)

Milk

Yoghurt

Cheese T/P

Cheese T/C

Quark

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

Kineticssystem: 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

inte

grat

ed

aco

ust

ic s

gnal

(a.

u.) saliva

cream 2 s

cream 2,3 s

cream 2,7 s

cream 2,9 s

cream 3,1 s

time

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

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

CRISPY AND CRUNCHY


Texture

technologies

Texture

technologies

Chocolate rice cracker


Smaller bits quickly get softened by saliva

fractering sound disappears

Single bite:

about 10 chews

Comparison between crispy

and/or crunchy food products• Fresh from the pack


First bitesLoudest of first 3 bites


• 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

Duration of sound from the first biteloudest of first 3 bites


Fracture propagates laterally through a thin sheet

Teeth squash through a thick layer of material

Cruchiness

• Extented sequence of sound generating

chews ( > 3 kHz)


Pringles

Dorito’s

Nibbits

Lay’s natural

“typewriter song”

Leroy Anderson (1950)

Henri Matisse (1910)

Stailing

• Loss of crispy chrunchy behaviour in the open

air: first bites 0, 1 and 5 h


Mixed chewing and rubbingChewing a cashew nut and intermittent tongue rubbing


chewingrubbing 0 rubbing 1 rubbing 2 rubbing 3 rubbing 4

chewing chewing chewing

nativelarge

particlesformed

• Large particles disappearfrom oral coating

• Lubrication increases(fat, viscous bolus?)

Particles

Lubricationby fat

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

Understanding and control of oral

processing has greatly supported

product development




Creating the future together

www.nizo.com

[email protected]

www.insightfoodinside.com

[email protected]

out of the sensory box final

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