Unraveling Food Digestion -Challenges and Opportunities
for Food Scientists
R. Paul Singh
University of California, Davis
Food Chain
Farm to Fork
Drying
Physical Properties
Air-Impingement Systems
Freezing
Modified Atmosphere Packaging
Frying
Thawing
Grilling
Shelf life
Time-Temperature Integrators
Energy Accounting
Water Use

Link between physical and material
properties of foods and nutrient
release from foods in the GI tract?
Role of Food Material Properties and Disintegration Kinetics in Gastric Digestion
USDA NRI 2008-12
Food Matrix and Nutrient
Bioavailability
Nutrient
b-carotene
Food
Matrix state
Bio-availability
Reference
Carrot
Raw
19-34%
Van het Hof et
al. (2000)
Carrot
Carrot Juice
70% higher than raw
Castenmiller et
al (1999)
Food Matrix and Nutrient
Bioavailability
Nutrient
b-carotene
a- tocopherol
Food
Matrix state
Bio-availability
Reference
Carrot
Raw
19-34%
Van het Hof et
al. (2000)
Carrot
Carrot Juice
70% higher than raw
Castenmiller et
al (1999)
Broccoli
Different cooking
methods
480%-530% higher
than raw
Bernhardt &
Schlich (2005)
Food Matrix and Nutrient
Bioavailability
Nutrient
b-carotene
Food
Matrix state
Bio-availability
Reference
Carrot
Raw
19-34%
Van het Hof et
al. (2000)
Carrot
Carrot Juice
70% higher than raw
Castenmiller et
al (1999)
a- tocopherol
Broccoli
Different cooking
methods
480%-530% higher
than raw
Bernhardt &
Schlich (2005)
Lutein
Tomato
Tomato paste
22%-380% greater
plasma response
than fresh tomato
Van het Hof et
al. (2000)


Almonds are one of the richest sources of
dietary vitamin E with benefits to reducing
risk of CHD and certain cancers.
Only about 45% of vitamin E was
bioaccessible from powdered almonds.
Bioaccessibility
Proportion of a nutrient that
can be released from a
complex food matrix and
potentially available for
absorption in GI tract
Samples obtained via
ileostomy after 3.5 hr of
digestion. Volunteers fed
2 mm cube raw almonds
Mandalari et al. (2008) J Ag Food Chem
Food Disintegration in the GI Tract
• Oral processing
• Gastric digestion
Digestion system
•
•
The overall function
– extract nutrients into
useable form
– absorb nutrients
– eliminate unneeded
materials
Food takes between 24-36
hours to pass through the
gastrointestinal tract
Solid Food Disintegration
in the Stomach
-Stomach emptying
-Satiety, Obesity
-Nutrient release
-Food safety:
- Allergens
-Nanoparticles
Stomach
• Volume: 50ml to 4 liters of liquid
– Chemical digestion by enzyme activity
– Mechanical digestion by the mixing in the
stomach
Stomach
• Volume: 50ml to 4 liters of liquid
– Chemical digestion by enzyme activity
– Mechanical digestion by the mixing in the
stomach
• Gastric juice: Colorless fluid
– 1.5 L secreted/day
– Hydrochloric acid
• breaks the food apart and kills most of the
bacteria that you swallow
– Mucus (~1.5 g/L)
• forms a gelatinous coating over the
mucosal surface.
– Pepsin (~ 1 g/L)
• proteins broken down into smaller
polypeptide chains
– Salt, Gastric Lipase
• fat digestion begins here
Antrum
Antrum
• Fundus: begins digestion
of proteins and mixes
together stomach
contents.
Antrum
• Fundus: begins digestion
of proteins and mixes
together stomach
contents.
• Body: digests proteins
and blends materials in
stomach and reduced to
a paste
Antrum
• Fundus: begins digestion
of proteins and mixes
together stomach
contents.
• Body: digests proteins
and blends materials in
stomach and reduced to
a paste
• Antrum: Breaks down
large food material into
small particles
Antrum
• Pyloric sphincter: a
specialized valve that
selectively empties the small
particles and retains the large
• Fundus: begins digestion
of proteins and mixes
together stomach
contents.
• Body: digests proteins
and blends materials in
stomach and reduced to
a paste
• Antrum: Breaks down
large food material into
small particles
Dynamic MRI image series showing propagating antral contraction waves (small
arrows) displayed in time intervals of 10 s. (Schwizer and others 2006)
Antral contraction of stomach
Propulsion, grinding, and retropulsion of solids by peristaltic
contractions of distal stomach (Kelly 1980)
• From an engineering perspective, the
human stomach is a receptacle, a grinder, a
mixer and a pump that controls the digestion
process.
• From an engineering perspective, the
human stomach is a receptacle, a grinder, a
mixer and a pump that controls the digestion
process.
• Consider stomach to be a flexible wall
reactor, with peristaltic wall motility.
• From an engineering perspective, the
human stomach is a receptacle, a grinder, a
mixer and a pump that controls the digestion
process.
• Food enters the stomach through the oesophagus
as a bolus
• Bolus disintegration ?
• Solid particulate disintegration ?
Develop a realistic computeraided model of the human
stomach and study flow
characteristics and solid
disintegration
3D MODEL-AVERAGE SIZED HUMAN
STOMACH
• Average dimensions*
–
–
–
–
Greater curvature ≈ 31 cm long.
15 cm wide (at its widest point).
Pylorus’ diameter is ≈ 1 cm.
Stomach’s capacity is about 0.94 L.
Volume = 0.9 L
Max width = 10 cm
Pylorus
diameter 1.2 cm
* Keet, 1993; Schulze, 2006.
Max curvature = 34 cm
25
GASTRIC MOTILITY
• The motility of the stomach wall can be characterized
by three types of muscle contractions.
– Slow and weak contractions that originate
and develop in the upper part of the
stomach.
– A series of regular-peristaltic contraction
waves (ACWs) that originate in the middle
of the stomach, and propagate towards
the pylorus.
– A tonic contraction of the entire gastric wall
that allows the stomach to accommodate
itself to varying volumes.
Fundus
Body
Pyloric
canal
Antrum
GASTRIC MOTILITY
• Despite recent advances in imaging technologies, the motility
pattern of the gastric wall is still poorly characterized.
• The dynamics of ACWs is the only motor
activity experimentally characterized.
– By using MRI techniques, the motility of ACWs
was tracked during 20 minutes after the
ingestion of 500ml of a 10% glucose solution
(Pal et al., 2007).
Fundus
Body
Pyloric
canal
Antrum
27
GASTRIC MOTILITY DURING
DIGESTION
ACW dynamics:
• Initiated every 20s at 15cm from the
pylorus.
• Relative occlusion of ACWs: from 0
to 80%.
1
4
3
2
28
30%
40-80%
30-40%
0-30%
FLUID MOTIONS IN THE STOMACH
2.75e-02
2.61e-02
2.47e-02
2.34e-02
2.20e-02
2.06e-02
2.75e-02
• The strongest fluid
motions were
predicted within the
lower part of the
stomach model.
• The rheological
properties of gastric
contents has a
significant effect on
the behavior of the
antropyloric flow.
1.92e-02
2.61e-02
2.47e-02
1.79e-02
2.34e-02
1.65e-02
2.20e-02
1.51e-02
2.06e-02
1.37e-02
1.92e-02
1.24e-02
1.79e-02
1.10e-02
1.65e-02
9.62e-03
1.51e-02
1.37e-02
8.24e-03
1.24e-02
6.87e-03
1.10e-02
5.50e-03
9.62e-03
4.12e-03
8.24e-03
2.75e-03
6.87e-03
Y
1.37e-03
5.50e-03
Z
X
4.12e-03
0.00e+00
2.75e-03
Y
1.37e-03
Z
Contours
Velocity Magnitude (m/s)
X
of0.00e+00
Velocity Magnitude
(m/s) (Time=4.8001e+01)
Contours of Velocity Magnitude (m/s) (Time=4.8001e+01)
FLUENT 6.3
29
FLUENT 6.3 (3d, pbns
RHEOLOGICAL PROPERTIES OF GASTRIC
CONTENTS
•
Fluid-dynamics of three different liquid meals were investigated.
– Newtonian fluid ( =  ).
• Water:  =1 cP.
– Newtonian fluid ( =  ).
• Honey:  =1000 cP.
– Non-Newtonian ( = K n).
• Tomato juice (5.8 %):
K = 0.223 Pa.sn
n = 0.59.
ANTROPYLORIC FLOW MOTION
• Effect of viscosity on the formation of the retropulsive jetlike structure.
3.97e-02
2.76e-02
3.77e-02
vmax = 2.8 cm/s
2.62e-02
2.48e-02
2.34e-02
3.38e-02
3.18e-02
2.21e-02
2.98e-02
2.07e-02
1.93e-02
2.78e-02
1.79e-02
2.58e-02
1.66e-02
2.38e-02
1.52e-02
2.18e-02
1.38e-02
1.99e-02
1.24e-02
1.79e-02
1.10e-02
1.59e-02
9.65e-03
1.39e-02
8.28e-03
1.19e-02
6.90e-03
9.93e-03
5.52e-03
7.94e-03
4.14e-03
5.96e-03
2.76e-03
1.38e-03
0.00e+00
vmax = 4.0 cm/s
3.57e-02
Newtonian
(1 cP)
Y
Z
3.97e-03
3.54e-02
X
1.99e-03
3.37e-02
3.19e-02
3.01e-02
Pathlines Colored by Velocity Magnitude (m/s) (Time=4.8001e+01)
2.84e-02
2.66e-02
Newtonian
(1000 cP)
Y
Z
X
0.00e+00
vmax = 3.6 cm/s
Pathlines
Colored
Jun 19,
2009 by Velocity Magnitude (m/s) (Time=4.8252e+01)
FLUENT 6.3 (3d, pbns, dynamesh, lam, unsteady)
2.48e-02
2.30e-02
2.13e-02
1.95e-02
1.77e-02
1.60e-02
• No retropulsive jet-like
structure developed.
• Higher and more localized
retropulsive velocities were
predicted at the peak of the
ACW.
Jan 15, 2010
FLUENT 6.3 (3d, pbns, dynamesh, lam, unsteady)
1.42e-02
1.24e-02
1.06e-02
Non-Newtonian-shear thinning
(40-570 cP)
8.86e-03
7.09e-03
5.32e-03
3.54e-03
1.77e-03
Y
Z
X
9.37e-09
Pathlines Colored by Velocity Magnitude (m/s)
May 18, 2010
ANSYS FLUENT 12.1 (3d, pbns, lam)
31
• Effect of viscosity on the formation of eddy
structures.
3.97e-02
2.76e-02
3.77e-02
2.62e-02
3.57e-02
2.48e-02
3.38e-02
2.34e-02
3.18e-02
2.21e-02
2.98e-02
2.07e-02
1.93e-02
2.78e-02
1.79e-02
2.58e-02
1.66e-02
2.38e-02
1.52e-02
2.18e-02
1.38e-02
1.99e-02
1.24e-02
1.79e-02
1.10e-02
1.59e-02
9.65e-03
1.39e-02
8.28e-03
1.19e-02
6.90e-03
9.93e-03
5.52e-03
7.94e-03
4.14e-03
5.96e-03
2.76e-03
1.38e-03
0.00e+00
Newtonian
(1 cP)
Y
Z
3.97e-03
3.54e-02
X
1.99e-03
3.37e-02
Newtonian
(1000 cP)
Y
Z
X
0.00e+00
3.19e-02
3.01e-02
Pathlines Colored by Velocity Magnitude (m/s) (Time=4.8001e+01)
2.84e-02
2.66e-02
Pathlines
Colored
Jun 19,
2009 by Velocity Magnitude (m/s) (Time=4.8252e+01)
FLUENT 6.3 (3d, pbns, dynamesh, lam, unsteady)
2.48e-02
2.30e-02
2.13e-02
Jan 15, 2010
FLUENT 6.3 (3d, pbns, dynamesh, lam, unsteady)
• Eddy structures are confined
to smaller regions closer to
the gastric walls.
1.95e-02
1.77e-02
1.60e-02
1.42e-02
1.24e-02
1.06e-02
Non-Newtonian-shear thinning
(40-570 cP)
8.86e-03
7.09e-03
5.32e-03
3.54e-03
1.77e-03
Y
Z
X
9.37e-09
Pathlines Colored by Velocity Magnitude (m/s)
May 18, 2010
ANSYS FLUENT 12.1 (3d, pbns, lam)
32
RESULTS: VISCOSITY AND
LUMINAL PRESSURE
• Effect of viscosity on the pressure
gradients within the stomach.
Pmax = 6.5x10-3 mmHg
Pmax = 1.2 mmHg
Newtonian
(1000 cP)
Newtonian
(1 cP)
Pmax = 0.1 mmHg
Non-Newtonian-shear thinning
(40-570 cP)
33
VISCOSITY AND LUMINAL
PRESSURE
• The higher pressures that develop within the
stomach, may improve the mechanical
digestion of solid meals by:
– Improving the mechanical breakdown of food particles.
– Increasing the distension of the antral wall (i.e. by
modifying the motility pattern of the stomach wall).
Fparticle-wall
Fpressure
Particle Strength Threshold
Maximum force supported by the particle
Fparticle-particle
34
PARTICLE MOTION - NEWTONIAN 1cP
• These results are in good agreement with experimental
data obtained using real-time ultrasonography.
– Brown et al. (1993) tracked the
motion of solid particles associated
with the ingestion of 500 mL of clear
chicken broth with five 5 garbanzo
beans cut in half.
Shuttling of particles by antral
contractions (Review article)Schulze, 2006.
“…immediately after ingestion of the test meal, the beans, which
were heavier than the surrounding liquid, were retained in the
dependent portion of the stomach.”
“…liquid passed over the beans which, for the most part, were
retained along the gastric greater curve in the gastric sinus.”
Brown et al., 1993.
35
In vitro Systems
• To study food disintegration and digestion
Canard Digerateur
Jacques de Vaucanson, 1739
The Digesting Duck
Voltaire wrote that "without...the duck of Vaucanson, you will have nothing to remind
you of the glory of France."
("Sans...le canard de Vaucanson vous n'auriez rien qui fit ressouvenir de la gloire
de la France.")
TNO intestinal model (TIM)
Stomach
pH electrode
Hollow fiber membranes
simulating the absorption
Intestine
TNO Nutrition and Food
Research (Zeist, The
Netherlands)
The model gut
Institute of Food Research,
Norwich Research Park, Colney,
Norwich NR4 7UA, UK
Needs in Pharmaceutical research
• “... mechanical functions of stomach and
duodenum are well defined in terms of
viscoelastic properties, movement patterns of
their walls….flow phenomenon to digestion
remains to be established…contribution of
pressure forces, shear stresses, flow reversals
and vortical flow remains to be quantified.”
Schulze (2006)
In Vitro Dissolution Testing of Oral
Dosage Forms: USP apparatus
•
•
•
•
•
•
Apparatus 1 - Basket (37º)
Apparatus 2 - Paddle (37º)
Apparatus 3 - Reciprocating Cylinder (37º)
Apparatus 4 - Flow-Through Cell (37º)
500 ml –1000 ml (900 ml)
Agitation speed: 50-100 rpm for basket method, and 25-75 rpm for
paddle method.
• Aqueous dissolution medium composed of 0.1 N HCl (or pH 1.2)
Food Disintegration System
• Food Disintegration system
- Custom-built turntable
- Glass chamber
- Stainless steel annular container
- Force measuring apparatus
• Useful in studying dissolution and
disintegration kinetics of
individual food particulates
Food Disintegration System
GP-22 ABS plastic
beads (~3 mm dia)
•
•
•
Custom-built turntable
Jacketed glass chamber
On-line Force measuring apparatus
Sample holder
Kong and Singh (2008) J Food Sci
Profile of periodic force
0.35
Force (N)
0.28
0.21
0.14
0.07
In vivo
0
0
5
10
Time (min)
In vitro
Vassallo MJ, et al. 1992.
Typical disintegration profiles
1.2
Wt/W0
0.8
0.6
0.4
0.6
0.4
0.2
0
0
5
10
15
20
Disintegration time (min)
Roasted
almond
1
0.8
0.2
0
Raw carrot
1
Ham
Wt/W0
1
Wt/W0
1.2
1.2
0.8
0.6
0.4
0.2
0
0
10
20
30
Disintegration time (min)
• Exponential: canned kidney beans, ham, Gummy
bear candy, apple bar
• Sigmoidal: fruits such as raw carrots
• Delayed sigmoidal: dry foods such as peanuts,
almonds, fried dough products
In vivo stomach emptying curves from
scintigraphy data
(Camilleri et al. Am J Physiol 249: G580–G585.)
0
10
20
30
40
Disintegration time (min)
50
Carrot disintegration
1.1
Raw carrot, 0.015 N
0.9
2-min-cooked
carrot, 0.017N
0.8
6-min-cooked
carrot, 0.017N
0.7
50
Raw carrots
2-min-cooked carrots
6-min-cooked carrots
40
Hardness (N) .
Wt/W0
1
0.6
0.5
0.4
30
20
10
0.3
0.2
0
0
20
40
60
80
Time (min)
Disintegration profiles of carrot
(n=6)
100
0
10
20
30
40
Soaking time (min)
Hardness of carrot in gastric juice
(n=8)
• The different profiles are a result of competition among surface erosion,
texture softening and absorption of gastric juice
50
Simultaneous surface erosion, absorption of gastric
juice and texture softening
1.2
1
Wt/W0
0.8
0.6
0.4
0.2
a)
0
Disintegration time (min)
Erosion front
1.2
1
b)
Wt/W0
0.8
0.6
0.4
0.2
Food particulate
during digestion
c)
Tenderization front Soft layer
0
Disintegration time (min)
1.2
1
Wt/W0
0.8
Tenderization front
0.6
0.4
0.2
Soft layer
Absorbed water
0
Disintegration time (min)
Penetration front
Carrot (Methylene blue)
Penetration front of gastric juice in
carrot
Pectin
Cell wall
Penetration front
of gastric juice
Carrot
Categorize foods based on their structural
breakdown in gastric environment?
• Linear-exponential equation:
y (t )  1  k  b  t   e
1.2
- b t
Delayed sigmoidal
Sigmoidal
Exponential
1
– k: increase in weight with time t
(min)
– β: the concavity of the time-weight
retention relationship (β >0)
Wt/W0
0.8
0.6
0.4
0.2
Candy, apple bar, Canned kidney
beans
<5 min
Ham, breakfast pretzels, fried
dough (no yeast)
5-10 min
Apple, raw carrots
10-20 min
Raw almond and peanut
>10 hours
0
0
10
20
30
40
Disintegration time (min)
• Half time( t1/2)
- Can be derived by regression
- Express as disintegration rates
50
Effect of viscosity
120
Half time (min)
)
100
80
y = 52.378e68.286x
R2 = 0.9956
60
40
20
0.0%
0.2%
0.4%
0.6%
0.8%
1.0%
1.2%
Gum concentration (%)
Effect of gastric viscosity on carrot disintegration
• Increase in the viscosity of gastric content delays food disintegration
Peanut digestion
y (t )  1  k  b  t   e - b t
1.2
1
0.8
0.6
Raw
Boiled
Roasted
Fried
0.4
0.2
12
0
0
50
100
150
200
250
Disintegration time (min)
300
350
Half time (hrs) .
Weight retention ratio .
1.4
10
8
6
4
2
0
Raw
boiled
roasted
fried
Almond digestion
• Satiety properties of almonds?
12
t1/2 (hrs)
10
8
6
4
2
0
Raw
Roasted
• Slow disintegration and swelling in the
stomach contribute to satiety feeling
Human Gastric Simulator (HGS)
• Create peristaltic movement of walls
• Simulate gastric secretion (enzyme and acid) and stomach emptying
• Study size distribution of food particulates in digesta, nutrient release, and rheological
properties
• Study physiological effects (pH, emptying, contraction) on digestion
Comparison of stomach forces
between in vitro and in vivo
3.5
Force (N)
3
2.5
2
1.5
1
0.5
0
0
2
4
6
Time (min)
Profile of contraction force. Left: in vitro force created in the bottom of
HGS simulating antral force in human stomach; right: in vivo force profile
obtained from stomach proximate to antrum (Vassallo et al. 1992. Am J
Physiol Gastrointest Liver Physiol 263: G230–9.)
Comparison of gastric pH between
in vitro/in vivo
6
5
pH
4
3
2
1
0
0
1
2
3
4
Hours
Profiles of pH. Left: pH of the emptied fluid of HGS; right: in vivo gastric
pH; red rectangle area indicates the pH after food intake (Malagelada et
al. 1976. Gastroenterol 70: 203-10)
Dry solids percentage (%) .
Comparison of disintegration efficiency
between HGS and shaking bath
80
70
60
HGS
Shaking bath
50
40
30
20
10
0
d>6.3
4<d<6.3
2.8<d<4
d<2.8
Particle size (mm)
Comparison between particle size distribution of apple after digestion
in HGS and shaking bath (mean of three trials)
In vivo trials
 Human trials
June 6, 1822
Mackinac Island
Michigan
Alexis St. Martin
Experiments and
observations on the
gastric juice and
the physiology of
digestion
By
William Beaumont,
Experiments and
observations on
the gastric juice
and the physiology
of digestion
By
William Beaumont,
In vivo methods to assess gastric
disintegration and emptying rate
• Feeding study
– acquiring the digesta samples using naso-gastric tube
• Intubation techniques: gastric barostat and intraluminal
manometry
– “gold standard” for assessing motility of the stomach
In vivo methods to assess gastric
disintegration and emptying rate
• Feeding study
– acquiring the digesta samples using naso-gastric tube
• Intubation techniques: gastric barostat and intraluminal
manometry
– “gold standard” for assessing motility of the stomach
• Scintigraphic imaging: liquid barium sulphate, radioopaque
spheres
– standard method to measure gastric emptying
• Ultrasonography measures gastric volume or antral crosssection. The information is used to estimate the rate of emptying
and evaluate antral motility.
• Magnetic resonance imaging (MRI)
• Indirect methods such as blood test and breath test
Scintigraphic
images shows
capsule
disintegration and
gastric emptying of
its contents)
Gamma
scintigraphy
www.bio-images.co.uk/AAPS2002.pdf
MRI images showing disintegration and
gastric emptying of drug tablet
MRI
www.pharmprofiles.co.uk/UserFiles/File/pdf/DepomedPresentation.pdf
In vivo trials
 Animal trials
 Rats
 Pigs


Canulated
Euthanized
Canulated Cow
http://t1.gstatic.com/
In vivo trials
Pigs Arrive at Housing
Facility
Massey University New
Zealand
Meal Preparation
Feeding Trials using Pigs

Obtain in vivo data examining impact of various
conditions on food digestion -- 96 pigs

Processing



Digestion time




White rice (cooked)
Brown rice (cooked)
20 min
60 min
120 min, 180 min, 300 min
Location in stomach


Fundus/body
Antrum
*Approved by the Massey University Ethics
Committee*
Sampling
 Pigs euthanized at 0, 60, 120, 180, or 300 min after
eating brown or white rice meal
Food Reservoir?
Proximal Region
Main location for
breakdown?
Mixing
between
regions??
Distal Region
69
Methods

Samples taken from body/fundus & antral
regions
Key Measurements
esophagus
Texture
Rheological properties
pH
Moisture content
Particle size distribution
Pyloric sphincter
Results:
20 min white rice
More “liquid-like”
portion in antrum
Results: 20 min brown rice
Evidence of “antral grinding” 
outer bran layer broken off of
inner endosperm layer
Rice Gastric Digestion: 20 mins
Brown Rice
White Rice
300 min digestion
Brown rice -- antrum
White rice -- antrum
20 min digestion
1000
900
800
shear stress (Pa)
700
600
500
400
300
200
white proximal
white distal
brown proximal
brown distal
100
0
0
0.5
shear rate (1/sec)
1
Data points are experimentally measured values. Lines represent Hershel-Bulkely model predictions.
20 min digestion
1000
900
800
shear stress (Pa)
700
Difference between
proximal & distal regions
600
500
400
300
200
white proximal
white distal
brown proximal
brown distal
100
0
0
0.5
shear rate (1/sec)
1
Data points are experimentally measured values. Lines represent Hershel-Bulkely model predictions.
120 min digestion
1000
900
white proximal
white distal
brown proximal
brown distal
800
shear stress (Pa)
700
600
500
400
300
200
100
0
0
0.5
shear rate (1/sec)
1
Data points are experimentally measured values. Lines represent Hershel-Bulkely model predictions.
120 min digestion
1000
900
white proximal
white distal
brown proximal
brown distal
800
shear stress (Pa)
700
600
500
400
Less difference between
proximal &
distal regions
300
200
100
0
0
0.5
shear rate (1/sec)
1
Data points are experimentally measured values. Lines represent Hershel-Bulkely model predictions.
120 min digestion
1000
900
white proximal
white distal
brown proximal
brown distal
800
shear stress (Pa)
700
600
500
400
Less difference between
proximal &
distal regions
300
BUT…
Greater difference between
brown & white rice
200
100
0
0
0.5
shear rate (1/sec)
1
Data points are experimentally measured values. Lines represent Hershel-Bulkely model predictions.
Rice Grain Compression
60
Brown Rice Proximal
White Rice Proximal
Brown Rice Distal
White Rice Distal
50
peak force (N)
40
30
20
10
0
20
60
120
180
digestion time (min)
300
480
Rice Grain Compression
60
Brown Rice Proximal
White Rice Proximal
50
Brown Rice Distal
White Rice Distal
Firmness decreases with time
 Increased breakdown
peak force (N)
40
30
20
10
0
20
60
120
180
digestion time (min)
300
480
Rice Grain Compression
60
Brown Rice Proximal
White Rice Proximal
50
Brown Rice Distal
White Rice Distal
Distal < Proximal
More breakdown in Antrum
peak force (N)
40
30
20
10
0
20
60
120
180
digestion time (min)
300
480
In Vivo Trial with Raw and Roasted
Almonds



Animal Housing

72 male pigs (23 ± 1.5 kg)

Housed in metabolic cages

7 day acclimation period
Diet Preparation

Raw & roasted, medium diced almonds

Individual meals prepared 2x daily
Final meal

Prior to final meal 18 hr fast

2 hr without water

Meal of only almonds
Gastric Emptying: Processed Foods
Roasted Almonds & White Rice Gastric Emptying
120%
% dry matter remaining
100%
Roasted Almonds Linear Model
y = -0.0005x + 1.0304
R² = 0.9901
80%
60%
White Rice Linear Model
y = -0.0017x + 0.9398
R² = 0.9992
40%
20%
White Rice
Roasted Almonds
0%
0
100
200
300
400
500
digestion time (min)
600
700
800
Unpublished Data
Gastric Emptying: Less Processed
Raw Almonds & Brown Rice Gastric Emptying
120%
% dry matter remaining
100%
Raw Almonds Power Model
y = 1.6199x-0.13
R² = 0.9091
80%
60%
Brown Rice Linear Exponential Model
y = (1+ 0.844*0.006x)*e(-0.006x)
R2 = 0.996
40%
Raw Almonds
20%
Brown Rice
0%
0
100
200
300
400
500
digestion time (min)
600
700
800
Unpublished Data
Mixing of Digesta in Stomach
50% of daily dry matter requirement of almonds
 25% water
 0.3% indigestible marker evenly mixed with
sample



Titanium dioxide (TiO2)
Chromium oxide (Cr2O3)
Particle Mixing using Markers
 Each meal  divided into 2 portions
Particle Mixing using Markers
 Each meal  divided into 2 portions
 Portion 1: Titanium Dioxide (TiO2)
Esophagus
Proximal
Region
ion
Distal Reg
Particle Mixing using Markers
 Each meal  divided into 2 portions
 Portion 1: Titanium Dioxide (TiO2)
 Portion 2: Chromium Oxide (Cr2O3)
Esophagus
Proximal
Region
ion
Distal Reg
Raw Almond Digestion
Chromic oxide “portion”
Titanium dioxide “portion”
20 min
Raw Almond Digestion
8
8
7
7
10
9
6
6
5
4
2
1
5
10
9
4
2
3
3
20 min
1 hour
1
Mixing Index Calculation
 Difference between variance (s2t) and equilibrium
variance (s2∞) drives mixing
 Mixing index:
 s2t = variance at time t
s t2 - s 2
M 2
2
 s 0 = long time variance
s 0 - s 2
 s20 = initial variance
 Evolution of mixing indices over time to determine
rate of mixing:
ln( M )  -kmix * t
 t = time elapsed
 kmix = mixing rate constant
References: Smith, 2003; Schofield, 1976
Mixing Index Calculation: Cr
4.5
White Rice
Brown Rice
4.0
3.5
White
Rice:
White Rice
kmix,Cr
= 7.8
* 10-3
-ln(M)
= 0.0078t
R2 = 0.95
1/min
-ln(M)
3.0
2.5
2.0
Brown
Brown
Rice Rice:
-3
-ln(M)
= 0.0064t
kmix,Cr
=
6.4
*
10
R2 = 0.96
1.5
1/min
1.0
0.5
0.0
0
100
200
300
digestion time (min)
400
500
Food Structure, textural
properties and digestion
Summary
Gastric digestion of foods remains a poorly
understood process
 A quantitative understanding is required to
develop next generation of foods for health
 Strong collaborations among food scientists
and engineers and researchers from medical,
nutrition, and pharmacology fields are
necessary to advance science in this area.

Gail Bornhorst
Maxine Roman
David Phinney
UC Jessica Widjaja
Davis Ryan Mayfield
Dr. Samrendra Singh
Dr. Maria Ferrua
Dr. Fanbin Kong
Dr. Jerry Xue
Research Staff at
Riddet Institute
Massey University
New Zealand