STLOpen Days 19-21 March 2019
Food microstructure and gastric digestion:
the egg white gel model
Françoise NAU
The nutritional value of food
can be modulated by food structuring
Food processing
Heat treatment
Acidification
Salting
Food Science Designing structure
Food structuring
Digestion
Macroscopic Molecular
Digestibility
Bioavailability
Allergenicity
Interactions
Bioactivity
Nutrition
Disintegration
Egg white (10% proteins) can lead to
various micro- and macro-structures
Ovalbumin Aggregates (low protein content)
pH 9 IS 0,03 M IS 0,03 M pH 7
IS 0,3 M pH 7
pH 5 IS 0,8 M
Linear (33 nm) Linear- branched (16 nm) Spherical (30 µm) Spherical- agglomerated (80 µm)
pH 9 IS 0,05 M
pH 7 IS 0,05 M
pH 5 IS 1 M
Egg White Gels (high protein content)
Smooth- rigid
Intermediate
Granular-spongy
1. Impact on the in vitro digestion process
The structure of ovalbumin aggregates and of egg white gels drives the protein digestibility and the nature of peptide released
during in vitro digestion
3. What happens in vivo?
Which impact on digestion process?
Which consequences on nutrient bioavailability?
Focus on gastric digestion
Does the Structure / Texture of EW Gels
modify the Gastric In Vivo Digestion
while keeping the composition constant ?
Experimental design
n=99
Te st m ea l: 1 kg E W G
Feeding
D ig es tio n tim e
1 trial = 1 EWG x 1 digestion time 5 to 6 pigs / trial
Euthanization Granular-spongy
EWG Intermediate
EWG Smooth-rigid
EWG
+ Blood sampling
Stomach sampling
Sample analyses
Stomach:
pH
Proteolysis degree (OPA method)
Granulometric distribution
Rheology measurements
Blood:
Free amino acid content
Results
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
0 40 80 120 160 200 240 280 320 360
Relative gastric dry matter amount
Digestion time (min) Granular-spongy EWG
Intermediate EWG Smooth-rigid EWG
Granular-spongy EWG Intermediate
EWG
Smooth-rigid EWG
0.250.300.350.400.450.50
Relative gastricdry matteramount at 360 min digestion
**p=0.0047
*p=0.0225
Granular-
spongy Intermediate Smooth-rigid
t1/2 (min) 204 207 246
ß 0.95 0.77 0.75
EWG
Elastic
modulus (Pa) Cohesiveness Granular-spongy 2268
± 3090.72
± 0.07Intermediate 2543
± 540.73
± 0.00Smooth-rigid 3854
± 2050.9
± 0.010.2 0.4 0.6 0.8 1 1.2 1.4
log(Area50)
Granular-spongy Intermediate Smooth-rigid
0.2 0.4 0.6 0.8 1 1.2 1.4
log(Area50)
Granular-spongy Intermediate Smooth-rigid
Proximal Distal
*** *** ***
*** ***
***
** * *
** *
***
*
Slower gastric emptying and *
Larger particle size
with the most elastic and cohesive
Smooth-rigid EWG
pH s ca le
Granular- spongy EWG pH 5
Intermediate EWG pH 7
Smooth-rigid EWG
pH 9
Uniform intra-gastric pH values,
equal to the initial EWG pH More than 4 h
to reach pH < 3
Slow acidification
High buffering capacity of EWG and high quantity ingested
pH s ca le
Granular- spongy EWG pH 5
Intermediate EWG pH 7
Smooth-rigid EWG
pH 9
Acidification starts at the pylorus region
HCl streaming along the stomach wall
pH s ca le
Granular- spongy EWG pH 5
Intermediate EWG pH 7
Smooth-rigid EWG
pH 9
Initial microstructure of the gels, not only initial pH,
More acidification
At the pylorus region for the smooth-rigid EWG In the proximal region for the intermediate EWG
Quicker and more homogeneous acidification
Easier HCl diffusion Inside the chyme for the granular- spongy EWG
Higher HCl streaming along gastric wall
for the smooth-rigid EWG Higher HCl diffusion
inside the chyme
for the intermediate EWG
Intragastric dry matter unaffected by EWG type
Particle size and distribution spread affected by EWG type
Storage and loss moduli affected by EWG type in both distal and proximal regions of the stomach
EW gels characteristics influence the physico-chemical parameters of the
gastric chyme, all along digestion
-20246Dim 2 (11.52%)
Granular-spongy EWG (pH5)
Intermediate EWG (pH7)
Smooth-rigid EWG (pH9)
20 min 60 min 120 min 240 min 360 min
-1.0 -0.5 0.0 0.5 1.0
-1.0-0.50.00.51.0
Dim 1 (31.23%)
Dim 2 (11.52%)
pHA pHB
pHC pHJ
DMJ AreaD
AreaP bD
bP
Visc0D
Visc0P ConsistD
ConsistP
RateIndexD
RateIndexP ThixoD ThixoP
G’D
G’G’’PD
G’’P
tandD
tandP
EWG Digestion time
