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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
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
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
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
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)
MOUTHFEEL
What do we sense?
7Together to the next level
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
8Together to the next level
Similar textural sensory attributes for
skin and mouth
• Thick, viscous
• Stiff, gelled
• Elastic
• Firm, hard
• Crumbly
• Stringy
9Together to the next level
• 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?
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
11Together to the next level
Slowly Adapting receptors:
sensitive to constant forces
• Rheology: bulk viscous forces
• Tribology: static surface friction
forces
BOUNDARY AND
HYDRODYNAMIC FRICTION
12Together to the next level
Transition to hydrodynamic lubrication
13Together to the next level
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 force
Lift
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
Together to the next level
Smaller particles
can slip through
Gap-width
increases with
viscosity 
Together to the next level
Fluidic food bolus
gapwidth
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
20Together to the next level
MUC5B; 10-40 MDa MUC7; 200 kDa
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
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
23
Together to the next level
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 TRIBOLOGY
Direct in-mouth measurement of boundary friction
Together to the next level
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)
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
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
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
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 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
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
33Together to the next level
Texture
technologies
Texture
technologies
Chocolate rice cracker
34Together to the next level
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
35Together to the next level
First bites
Loudest of first 3 bites
36Together to the next level
• 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 bite
loudest of first 3 bites
37Together to the next level
Fracture propagates laterally through a thin sheet
Teeth squash through a thick layer of material
Cruchiness
• Extented sequence of sound generating
chews ( > 3 kHz)
38Together to the next level
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
39Together to the next level
Mixed chewing and rubbing
Chewing a cashew nut and intermittent tongue rubbing
40Together to the next level
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
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
Together to the next level
43Together to the next level
Together to the next level
Creating the future together
www.nizo.com
george.vanaken@nizo.com
www.insightfoodinside.com
info@insightfoodinside.com

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out of the sensory box final

  • 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 Together to the next level 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? 7Together to the next level
  • 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 8Together to the next level
  • 9. Similar textural sensory attributes for skin and mouth • Thick, viscous • Stiff, gelled • Elastic • Firm, hard • Crumbly • Stringy 9Together to the next level • 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 11Together to the next level Slowly Adapting receptors: sensitive to constant forces • Rheology: bulk viscous forces • Tribology: static surface friction forces
  • 13. Transition to hydrodynamic lubrication 13Together to the next level
  • 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 Together to the next level 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 20Together to the next level 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 22Together to the next level Tongue scraping Saliva Guar Couva 760P OSA
  • 23. 23 Together to the next level 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 Together to the next level
  • 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 33Together to the next level Texture technologies Texture technologies
  • 34. Chocolate rice cracker 34Together to the next level 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 35Together to the next level
  • 36. First bites Loudest of first 3 bites 36Together to the next level • 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 37Together to the next level 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) 38Together to the next level 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 39Together to the next level
  • 40. Mixed chewing and rubbing Chewing a cashew nut and intermittent tongue rubbing 40Together to the next level 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 Together to the next level
  • 43. 43Together to the next level Together to the next level Creating the future together www.nizo.com george.vanaken@nizo.com www.insightfoodinside.com info@insightfoodinside.com