Oral processing in relation to perception of liquid

Together to the next level

Oral processing in relation to perception of liquid and semi solid food systems George van Aken

[email protected]

Jennifer Aniston (W Magazine photo shoot)

Science and Technology of Food Emulsions, June 2012


Introducing NIZO food research • Independent, private contract

research company for the food industry

• 200 professionals

• State-of-the-art facilities & food-grade processing centre

• HQ in “Food Valley” in The Netherlands

• Offices in France, UK, USA, Japan

• ISO 9001:2000 certified

HQ - Ede, The Netherlands

UK - Dr. Jean Banks

France - Mr. Damien Lemaire

USA / Canada - Dr. Ralf Jäger

Japan - Dr. Maykel Verschueren

Offices abroad:

Research centre

Processing centre Application centre

Technology for your success

Key question

How can we translate between

Food materials knowledge (rheological properties, molecular properties, structural dimensions)

and

Sensory perception of structures

(limiting to texture: hard, firm, tough, sticky, slimy, juicy, creamy, gritty, astringent)

3 Together to the next level

Product developers approach

Product development: composition, structure • reduced fat • thickeners • particles • aroma’s • sugar replacers

Product characteristics: sensory properties • not so creamy, thin, slimy, gritty • off tastes, off flavours, unbalanced

flavours

Sensory paneling

correlations

Instrumental measurements: • viscosity, gel strength, fracture behavior • friction measurement • droplet and particle size • aroma and flavour release

Correlations are often

poor


Contents


• Discussion of the main hurdles in relating structural and sensory properties

• Elucidating textural perception by the tongue

• Acoustic tribology

RELATING STRUCTURAL AND SENSORY PROPERTIES

Main hurdles

6



Vision

Touch

Sound

Mouthfeel

Taste

Smell

Senses:

1. Sensory response is multimodal Perception

Hedonic consumer response

Nutritional status

CCK, PYY, Gastrin, vagus nerve


Cross modal interactions: texture affecting flavour intensity perception

0 20 40 60 80

time (s)

Nos

e-sp

ace

conc

entr

atio

n (a

u) gel 1gel 2gel 3gel 4gel 5

(K. Weel, A. Boelrijk et al., published 2002)

Nose space

Texture-flavour interaction at perception level!

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 20 40 60 80time (s)

sens

ory

Inte

nsity

gel 1gel 2gel 3gel 4gel 5

Sensory intensity

hard

soft

2. Food is processed in the mouth


Mouth function as the first part of the gastrointestinal tract • Food preparation: mastication and addition

of saliva to form a cohesive slippery bolus that is safe to swallow

• Explore food content: • Nutritious? • Safe or toxic, flavor and aroma? • Sharp objects? Fishbones?

Undigestible grains?

//upload.wikimedia.org/wikipedia/commons/c/c5/Digestive_system_diagram_edit.svg

Criterium for swallowing: LOW RISK OF CHOKING

Risk of choking specific for humans, related to low position of the larynx, allowing a larger vocal range required for speach. Quick and clean passage through the pharynx into the esophagus, avoiding food spilling into the windpipe: A “clean” bolus should be formed


The food bolus should be: • cohesive, not disintegrating into loose particles

• soft and deformable enough to enter the (rather narrow) esophagus

• slippery and not sticking to the mucosa, allowing fast passage

After taste oral and

pharyngeal coating,

flavour release

Masticatory oral processing

many structural changes,

flavour release

Sensory perception of food

First bite rheology, temperature

Gut signals Satiety, well being

Brain

Receptors

Appearance color, shine,

structure, flow, aroma

swallow

Feed back



Sensory attributes along the oral processing pathway

First bite Masticatory After taste

temperature cooling

hardness crunchy

coating

fatty

creamy coating creamy viscosity

thick

sticky tacky

elastic cohesive tough

slippery

rough, astringent grainy, gritty

slimy

swallow time

taste, aroma

12

Needed

• Better understanding of how foods behave in the mouth

• Better understanding of how food is sensed

• Combine this knowledge with material science for product development


STUDIES ON FOOD EMULSION BEHAVIOUR IN THE MOUTH

Saliva, tongue surface, palating, chewing

14


Background research at TIFN

Examples of oral processing in relation to perception •Emulsions

•Emulsion-filled gels



•Emulsion filled gels


• In total 20 studies focussed on the effect of composition and oral processing of model food emulsions

• A lot of work! Each study: • 8-9 Female panellists (mean age 45-50 years) • General training to describe sensory attributes. • 2-4 training sessions on samples • 2-4 panelling sessions • 35 attributes

• 3 odor (O) • 8 taste (T) • 9 mouthfeel (MF) • 4 aftertaste (AT) • 11 afterfeel (AF)

Sensory analysis Quantitative Descriptive Analysis

Approach the first 7 QDA profilings

Standard emulsion

Fat content and fat type

Thickener

Particles

pH

Mixed emulsifiers Droplet size

Emulsifier Oil 10% WPI 1%

droplet size 1 μm pH 6.7

1st QDA profiling: variation of fat content, thickeners, particles, solid fat

Axis 1 (47.6%)

Axis 2 (43.7%)

AFsatiation

AFsticky

AFcoating

AFslimy

AFgrainy

AFrawtongue

AFrough AFdry

AFastringent

Mdry

Msalivaforming

Mmouthfilling

Mthick

Mslippery

Mcreamy Mfatty

skimmed milk

20% solid fat

0.3% guar gum

larger droplets

5% simplesse

5% WPI

10% solid fat

40% fat

20% fat

10% fat

5% fat 0% fat Texture attributes only

Vingerhoeds et al, Food Hydrocolloids, 2008

PCA plot

In low-viscosity systems: fat improves creaminess separate from thickness

WHY?

Oral behavior of emulsions: Large structural changes, even for thin liquid emulsions:

THIS is what you taste!

21 Together to the next level TI food and

Nutrition

40 % dairy emulsion (cream) 100x dilution with bidest

cream

after 1 min in mouth

Epithelial cells

Droplets and cells bound together by a ropy mucous mass from saliva and tongue surface

TI food and Nutrition

Emulsion viscosity & perceived thickness WPI-stabilized emulsions (ξ=potential < 0) (Vingerhoeds et al. Food Hydrocolloids, 23(3) (2009), 773-785.)

R2 = 0.9313 Emulsion:

0

10

20

30

40

50

60

70

80

90

0.001 0.01 0.1 viscosity (Pas) at 100 s-1

Mth

ick

sens

ory

scor

e

Φ = 2.5%

Φ = 10%

Φ = 10% + guar gum

Liquid emulsion

Theoretical curve (e.g. Krieger-Dougherty)

Best fit before mouth

Best fit in mouth

Spit out: R2 = 0.9925

Spit out


Interaction with the tongue PhD study of Diane Dresselhuis

Visualization of fat retention on piglet tongue

CSLM image (Nile blue staining) 500 500 m 10 wt% SF oil; 1 wt% WPI red: oil; green: tongue papillae

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

24 TI food and

Nutrition

Fat retention on the tongue

Fat adhesion and retention larger for more unstable emulsions → increased creaminess

emulsions varying in stability to coalescence o/w emulsion

7% SF (sunflower oil) stabilized with protein WPI

stable unstable WPI 1 0.3 [%] D[3,2] 0.92 1.15 [ m]

1.6 1.4 (@51 s-1) [mPa s]

gram

fat r

emai

ning

in m

outh

0.0

0.1

0.2

0.3

1% WPI SF 0.3 wt% WPI SF 1% WPI SF L

gram

fat r

emai

ning

in m

outh

spitrinse

0.0

0.1

0.2

0.0

0.1

0.2

0.3

1% WPI SF 0.3 wt% WPI SF 1% WPI SF L

gram

fat r

emai

ning

in m

outh

spitrinseFat remaining after first spit

Fat remaining after water rinsing

unstable stable

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


Nutrition

Effect of fat type on tactile oral perception

visc

osity

crystallinity

MARGINAL EFFECT (after) taste attributes only

E. De Hoog et al, in preparation

NO EFFECT G. van Aken, Food Hydrocolloids (2011)

EFFECT through partial coalescence

J. Benjamins et al, Hydrocolloids (2009)

rapeseed

sunflower linseed

soybean

fishoil

olive

ricine

MCT

Partial coalescence by fat crystals

Heating

Melts at in Mouth Temperature

Sunflower oil

Couva 760P

field of view: 3 x 4 mm

Spit-outs:

Jan Benjamins

Shear

homocoalescence

Heating

Viscous: more creamy

Larger droplets: no sensory effect

Fatty layer: more creamy

Effect of the deposition of a fatty layer on the tongue Friction between PDMS (hydrophobic) and glass (boundary friction regime)

Fat reduces the friction, but an increase in fat content has no further effect

0.0

0.2

0.4

0 10 20 30 40 Fat content (wt%)

Fric

tion

coef

ficie

nt

unstable emulsion stable emulsion

0.6

Fat content (wt%)

0.3 wt%WPI 1.0 wt%WPI

Effect of adsorption of fat onto the surface

Dresselhuis et al. Food Biophysics (2007)

Dewetting of saliva from the oral surfaces


Nutrition


Liquid emulsions sensory properties related to oral behavior

29

Droplet properties

Increase viscosity, enhanced by saliva

Bind to the oral mucous layer, Deposit fat

Thicker

SmootherFatter

Creamier mouthfeel


•Emulsion filled gels


Oral processing of emulsion-filled gels

mastication

Gel Viscous bolus of comminuted gel

saliva

breakup, dispersion, dissolution,

surface erosion

teeth, tongue rubbing,

saliva, heating

Sala et al., Food Hydrocolloids (2009), 23 (5) (2009), 1381-1393

The comminuted gel: in vitro and in expectorate

gel

•saliva

•water syringe

A viscous paste of gel fragments is formed

Viscosity of comminuted gel increases with oil content

Bound droplets:

Unbound droplets:

0

0.1

0.2

0.3

0.4

0.5

0.6

0 5 10 15 20 25

Oil concentration (g/ 100 g)

Visc

osity

(Pa

s)

κ-carr. bound

κ-carr. unbound

WPI bound

Shear rate= 100 s-1

The viscosity of the comminuted gel:

• primarily depends on the matrix

(κ-carrageenan > WPI)

• increases with the oil content

• depends on droplet-matrix interaction

In vitro masticated gels: effects of gel type and fat content

Emulsified oil:

• Increases the viscosity of the masticated bolus

(for gelatin unbound opposite)

• decreases the friction of the masticated bolus

(large effect)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.5 1 1.5 2Viscosity (Pa s)

Fric

tion

coef

ficei

nt

WPI

Carrageenan bound

Carrageenan unbound

Gelatin bound

Gelatin unbound

φ

φ

φ

φ

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.5 1 1.5 2Viscosity (Pa s)

Fric

tion

coef

ficei

nt

WPI

Carrageenan bound

Carrageenan unbound

Gelatin bound

Gelatin unbound

φ

φ

φ

φ

= 0, 5, 10, 20 wt% oil

Chojnicka et al., Food Hydrocolloids (2009), 23, 1038-1046 MTM tribometer

at 100 s-1

(rubber versus stainless steel)

Emulsion filled gels sensory properties related to oral behavior (after Guido Sala)

Effect on gel properties

Physicochemical mechanism

Effect on oral processing

Sensory attribute

More spreadable

Viscous bolus

Smoother tongue

Decrease fracture strain

Decrease fracture stress (polymer gels)

Stress concentration

Smaller gel fragments

Weaker fragments

Matrix properties

Droplet/ matrix interaction

‘ Viscosity ’ broken gel

Lubrication properties

Oil droplet release

Lower friction

Material properties

Droplet properties

More creamy

TACTILE PERCEPTION BY THE TONGUE

Toward understanding


Main regimes thickness perception Curve from: Shama, F. and P. Sherman (1973). J. Texture Studies 4: 111-118.


How can we explain the shape of this curve?

& shear rate (s -1 )

0 10 1 10 2 10 3 10 4 10 0

10 1

10 2

10 3

10 4

shea

r st

ress

(P

a)

&

Plot shear-stress versus shear-rate curves for food materials with very different shear thinning behaviour

Identify windows of food materials with similar perceived thickness

Sensitivity of the mechanoreceptors in the tongue

M. Trulsson, G.K. Essick, J. Neurophys. 1997(77), 737-748

Wire + force transducer


M. Trulsson, G.K. Essick, J. Neurophys. 1997(77), 737-748

Receptor types and sensitivities Slowly Adapting receptors: sensitive to constant forces Rapidly Adapting receptors: sensitive to force variations Assuming that forces on each RA receptor are additive: • Lower stress threshold of

about 12 Pa • Average stress threshold of

about 60 Pa


Main regimes thickness perception

shear rate (s -1 ) 10 0 10 1 10 2 10 3 10 4

10 0

10 1

10 2

10 3

10 4

shea

r st

ress

(P

a)

shear rate (s -1 ) 10 0 10 1 10 2 10 3 10 4

10 0

10 1

10 2

10 3

10 4

shea

r st

ress

(P

a)

shear rate (s -1 ) 10 0 10 1 10 2 10 3 10 4

10 0

10 1

10 2

10 3

10 4

shea

r st

ress

(P

a)

& Van Aken, G.A., Modelling texture perception by soft epithelial surfaces, Soft Matter, 2010, 6, 826–834

Viscous forces perceived

Thickness not necessarily related to perceived viscous forces

Curve from: Shama, F. and P. Sherman (1973). J. Texture Studies 4: 111-118.

Lower stress thresshold

Average stress thresshold

Sensitivity RA receptors Trullson, Essick, J. Neurophys. 1997(77), 737-748


What produces the forces sensed by the tongue?

Viscous forces of the fluid in motion relative to the tongue surface Friction of tongue and palate in

contact Particles grinding between

tongue and palate

palate

tongue


Tribological regimes (Stribeck curve)

Static friction

speed viscosity

Friction force

hydrodynamic

boundary

mixed

Only viscous forces

Static surface bonds

Transient surface bonds and corrugations

Liquid starts to interpenetrate

palate

papilla Gap-width increases with speed viscosity

Hydrodynamic modelling of the soft deformable papilla surface to calculate the gap width

Van Aken, Soft Matter (2010)


Papilla surface roughness and deformability Load dependence of contact area (OTC)

Frame size: 75 m * 125 m

Filiform papilla

Glass slide

- -

0 g load 48,10 g load

68,09 g load

96,89 g load 153,01 g load 209,7 g load

Els de Hoog

40 kPa Papilla surface roughness ~ 20 μm

1

10

100

1000

1 10 100 1000 10000

viscosity (mPas)

min

imum

gap

wid

th (m

icro

met

ers)

Papilla surface roughness

100 Pa, = 1 100 Pa, = 0 140 Pa, = 0

Pn (Shama & Sherman)

Forced flow; Thinning time

sensed; Viscous shear friction

sensed “THICK”

Slowed free flow; Viscous shear friction too small; Boundary

friction only if tongue is pressed

“CREAMY LIQUID”

Free flowing; Boundary

friction sensed

“RAW TONGUE”

Stir

red

yogh

urt

Ski

mm

ed m

ilk

Hon

ey

Mol

ten

choc

olat

e

Cre

am

Vege

tabl

e oi

l

Who

le m

ilk

Interaction with saliva 44



Fluidic food bolus: relevant forces and dimensions

gap

wid

th

45


Tactile perception of a fluidic food bolus

gap

wid

th

Smooth tongue

Sandpaper tongue

46


Low-fat hard cheese

Slowly hydrating dense cheese particles

Thin dilute emulsion of small droplets

47

Normal hard cheese

Forgeable particles, quickly hydrating

Viscous emulsion of coalesced droplets

Solids: breakdown path of fracturing an dissolution important

separation


Solids: hard cheese as example Mastication pathway (caricature)

gap

wid

th ~

de

tect

able

pa

rtic

le s

ize Full-fat

cheese

Low-fat cheese

48

PHYSICAL MEASUREMENT

Thickness Grittiness Astringent

49



Tactile perception of a fluidic food bolus

gap

wid

th

50

5 10 100 800

Speed (mm/s)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Trac

tion

Coe

ffici

ent (

-)

Silicon Rubber Load: 5N Temp.: 21°C

water

skim milk

whole milk

yoghurt 0% fat

yoghurt 3% fat

quark 0% fat

quark 10% fat

Liquid and soft semi solids: tribological studies

MTM tribometer yoghurt 3% fat

- Which speed? ? - Which load? - What about the interaction with saliva? - What about the actual oral surfaces?

- Papillae - Mucous epithelial layer - Variability (individuals, pre-meals, …)

Els de Hoog Hans Tromp

(NEW) Acoustic emission measurement of the in vivo scraping sound of the tongue

Example: Water - coffee with (whipping) cream

Line voltage as a function of time

water coffee with cream

Corresponding frequency spectrum of the cleaned signal

1,E-07

1,E-06

1,E-05

1,E-04

1,E-03

1,E-02

1,E-01

1,E+00

1 10 100 1000 10000 100000

amp

litu

de

(V

)

frequency (Hz)

water (saliva)

coffee with (whipping) cream

Fat content of milk


Interpretation: • tongue friction increased by milk protein (not observed by conventional

tribology), but is reduced in the presence of emulsified fat • translates to: skimmed milk more rough/dry/astringent than saliva, but

milk fat emulsion makes it smoother by improving lubrication

0,E+00

1,E-04

2,E-04

3,E-04

4,E-04

5,E-04

6,E-04

7,E-04

8,E-04

10 100 1000 10000 100000

aco

ust

ic s

ign

al (

a.u

.)

Frequency (Hz)

saliva

0,15 % fat

0,5 % fat

1,0 % fat

4,0 % fat

31,9 % fat

0,0E+00

5,0E-05

1,0E-04

1,5E-04

2,0E-04

2,5E-04

3,0E-04

3,5E-04

4,0E-04

inte

grat

ed

aco

ust

ic s

gnal

(a.u

.)

0,15 % fat

0,3 % fat

0,5 % fat

0,7 %fat

1,0 % fat

2,1 % fat

3,0 % fat

4,0 % fat

6,5 % fat

31,9 % fat


Comparison between dairy products

54

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

Kinetics system: cream after saliva

Observed are the effects of inhomogeneous mixing and finally a replacement of native mucosal layer by a lubricating fat layer 0,0E+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

Kinetics system: skimmed milk after cream

Observed are the effects of replacing the lubricating fatty coating with milk protein, followed by wear of the asperities on the papilla surface

0,0E+00

5,0E-05

1,0E-04

1,5E-04

2,0E-04

2,5E-04

inte

grat

ed

aco

ust

ic s

ign

al (

a.u

.)

31,9 % fat

0,07 % fat0,07 % fat

0,07 % fat

0,07 % fat

time

Applications acoustic tribology • Measurement tool for rough/astringent mouthfeel

o Low fat products o Astrigent products o High protein products

• Measurement tool for surface textures o Fabrics, wood, etc. o Good-grip surfaces o Non sweaty, non sticky

Publication in preparation

CONCLUSIONS


Conclusions

• Sensory food properties are often not directly related to food properties “on the shelf”

• Sensory food properties can be much better related to the food properties in the mouth, which change during mastication.

• A toolbox is available for accessing the effects of mastication and sensory correlation.

60



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Oral processing in relation to perception of liquid