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WATER VAPOR SORPTION
ISOTHERMS AND THE
CAKING OF FOOD POWDERS
WATER VAPOR SORPTION
ISOTHERMS AND THE
CAKING OF FOOD POWDERS
Laboratoire de Chimie Physique Industrielle
B.P. 1039- 51687 Reims Cedex2
M. Mathlouthi , B. RogM. Mathlouthi , B. Rog
WATER VAPOR SORPTION ISOTHERMS
WATER VAPOR SORPTION ISOTHERMS
CAKING OF FOOD POWDERS CAKING OF FOOD POWDERS
FACTORS AFFECTING THE CAKING OF SUGAR (control of flowability)
DECAKING OF SUGAR CONCLUSION
FACTORS AFFECTING THE CAKING OF SUGAR (control of flowability)
DECAKING OF SUGAR CONCLUSION
WATER VAPOR SORPTION
ISOTHERMS
WATER VAPOR SORPTION
ISOTHERMS
WATER VAPOR SORPTION ISOTHERMSBRUNAUER et al. (1938)
WATER VAPOR SORPTION ISOTHERMSWATER VAPOR SORPTION ISOTHERMSBRUNAUER BRUNAUER et al.et al. (1938)(1938)
5 types of isotherms5 types of isotherms2 %
Aw1
Type 1Type 1
Type 2Type 2
1Aw
0
2 %
Type 3Type 3
Aw1
2 %
Type 4Type 4
Aw10
2 %Type 5Type 5
Aw
1
2 %
BET isotherm (1+2) ex : swellable grainBET isotherm (1+2) ex : swellable grain
Langmuir isotherm: one layer Langmuir isotherm: one layer
BET S- shaped isotherm : multilayerBET S- shaped isotherm : multilayer
Flory-Huggins isotherm,ex: glycerolFlory-Huggins isotherm,ex: glycerol
BET isotherm: capillary+multilayerBET isotherm: capillary+multilayer
WATER VAPOUR SORPTION ISOTHERMWATER VAPOUR SORPTION ISOTHERM
Water vapour sorption isotherm : definition of the 3 regions
Water vapour sorption isotherm : definition of the 3 regions
REGION AREGION A corresponds to hydration monolayer where water molecules are bound to the product by strong H-bonds.
REGION CREGION C is that of the so-called free or solvent water. Water molecules in this region are much less strongly bound than in regions A and B. This fraction of water is available for mould growth or dissolving of soluble solutes.
REGION BREGION B corresponds to the linear part of sorption isotherm . Water is adsorbed as multilayers of molecules hydrogen bonded to the monolayer, or entrapped in the food by capillarity, Van der Waals forces,
SORPTION ISOTHERMS OF ANHYDROUS CRYSTALS
SORPTION ISOTHERMS OF ANHYDROUS CRYSTALS
0
0,05
0,1
0,15
0,2
0,25
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9Aw
W
a
t
e
r
c
o
n
t
e
n
t
(
g
/
g
M
.
S
.
) NaCl
Sucrose20C
SORPTION ISOTHERMS OF SALT HYDRATES
SORPTION ISOTHERMS OF SALT HYDRATES
0
0.5
1
1.5
2
2.5
3
3.5
0 10 20 30 40 50 60 70ERH %
W
a
t
e
r
c
o
n
t
e
n
t
(
g
/
1
0
0
g
M
.
S
.
)
LiClCaCl2
20C
LiCl, H2 O
CaCl2, H2 O
CaCl2, 2H2 O
00,1
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
Aw
W
a
t
e
r
c
o
n
t
e
n
t
(
g
/
1
0
0
g
M
.
S
.
)
SORPTION ISOTHERMS OF BETAINESORPTION ISOTHERMS OF BETAINE
Plateau between 12 % and 45 % ERH (Monohydrate)Water content = 0.15 g /g 1 H2O / betaine molecule Anhydrous stable between 0 et 7 % ERH
Plateau between 12 % and 45 % ERH (Monohydrate)Water content = 0.15 g /g 1 H2O / betaine molecule Anhydrous stable between 0 et 7 % ERH
Anhydrous
Monohydrate
Anhydrous 'Monohydrate
SORPTION ISOTHERMS OF DEXTROSE AND FRUCTOSESORPTION ISOTHERMS OF DEXTROSE AND FRUCTOSE
0
20
40
60
80
100
120
40 50 60 70 80 90 100ERH %
DextroseDextrose
FructoseFructose
20C
SORPTION ISOTHERMS OF SUGAR HYDRATES : Effect of temperatureSORPTION ISOTHERMS OF SUGAR HYDRATES : Effect of temperature
Anhy
drou
s
Monohy
drate
SORPTION ISOTHERMS OF HYDROPHILIC FOOD POLYMERS
SORPTION ISOTHERMS OF HYDROPHILIC FOOD POLYMERS
1 : Apple pectin 3 : potato starch2 : Casein 4 : Wheat starch5 : Cellulose
1 : Apple pectin 3 : potato starch2 : Casein 4 : Wheat starch5 : Cellulose
For For aaww < 0.4< 0.4 : : cellcell < pot < cas < < pot < cas < pectpect< < whewhe
For For aaww >0,4>0,4 ::celcel < cas < < cas < whewhe < pot < < pot < pectpect
APPLIED ASPECTS OF SORPTION ISOTHERMS
THERMODYNAMICAL ASPECTS- Sorption and desorption enthalpies- Water activity , sucrose solubility equilibrium- Heats of solution and crystallization
THERMODYNAMICAL ASPECTS- Sorption and desorption enthalpies- Water activity , sucrose solubility equilibrium- Heats of solution and crystallization
STRUCTURAL ASPECTS- Specific Area- Grain size and pores volume- Amorphous state and transition
STRUCTURAL ASPECTS- Specific Area- Grain size and pores volume- Amorphous state and transition
TECHNOLOGICAL ASPECTS-Drying conditions- Maturation and Stability- Handling, Storage and Packaging
TECHNOLOGICAL ASPECTS-Drying conditions- Maturation and Stability- Handling, Storage and Packaging
Method Observation Drawbacks
Microclimate 8-10 days for equilibration stability of temperatureaccurancy of water contentstability of saturated salt solutions
Method Observation DrawbacksElectrical hygrometer size of particles dissolution
high R.H. > 95 %
DETERMINATION OF SORPTION ISOTHERMDETERMINATION OF SORPTION ISOTHERM
CAKING CAKING
WATER ADSORPTION AND CAKINGWATER ADSORPTION AND CAKING
Schematic steps of lumpingSchematic steps of lumping
Solide
Air
Eau
Solide
Eau
SolideEau
a)
b)
c)
d)
Solide
Air
Eau
A- Pendular stepA- Pendular step
B- funicular stepB- funicular step
C- capillary stepC- capillary step
D- drop stepD- drop step
ERH
METHODS OF CHARACTERIZATION OF CAKING
METHODS OF CHARACTERIZATION OF CAKING
Flow rateFlow rate Flowability AngleFlowability Angle
Angle of reposeAngle of repose
Cohesion : Jenike cellCohesion : Jenike cell
Microscopical observationsMicroscopical observations
TRANSITION TEMPERATURE vs MOISTURE
Aguillera et al.,TIFS, 1995,6, 149
Tg of Sucrose using Gordon Taylor eq. ________
METHODS FOR PREVENTION OF CAKINGMETHODS FOR PREVENTION OF CAKING
Storage at low temperature Stabilisation of powder moisture and Temperature by maturation on indirect cooling
Drying to low moisture content Decaking : controlled humidification and dehydration
Addition of anti-caking agent
Storage at low temperature Stabilisation of powder moisture and Temperature by maturation on indirect cooling
Drying to low moisture content Decaking : controlled humidification and dehydration
Addition of anti-caking agent
CAKING OF
CRYSTALLINE
WHITE SUGAR
CAKING OF
CRYSTALLINE
WHITE SUGAR
1 mm
Pendular stepPendular step
0% < HRE < 44%0% < HRE < 44%
CAKING OF CRYSTALLINE WHITE SUGARCAKING OF CRYSTALLINE WHITE SUGAR
Solid
Air
Syrup
500 m
44% < HRE < 75%44% < HRE < 75%
Liquid bridge
Funicular stepFunicular step
CAKING OF CRYSTALLINE WHITE SUGARCAKING OF CRYSTALLINE WHITE SUGAR
Solid
Air
Liquid
75% < HRE < 85%75% < HRE < 85%
Solid bridge
Capillary stepCapillary step
CAKING OF CRYSTALLINE WHITE SUGARCAKING OF CRYSTALLINE WHITE SUGAR
Solid
Syrup
500 m
HRE> 85 %HRE> 85 %
Syrup surrounding crystalsSyrup surrounding crystals
SolidLiquid
Drop stepDrop step
CAKING OF CRYSTALLINE WHITE SUGARCAKING OF CRYSTALLINE WHITE SUGAR
WATER MIGRATION IN THE FILM OF SYRUP SURROUNDING THE CRYSTAL
WATER MIGRATION IN THE FILM OF SYRUP SURROUNDING THE CRYSTAL
Sugar crystal
Bound syrup film
Amorphous sugar layer
Inherent water
Water monomer
Sucrose
Water monomer
WATER IN SUGAR CRYSTALWATER IN SUGAR CRYSTAL
Air MoistureAir MoistureSyrup Water
Crystal sucrose
Syrup sucrose
Included water
PARAMETERS AFFECTING THE FLOW STABILITY OF SUGAR
PARAMETERS AFFECTING THE FLOW STABILITY OF SUGAR
GRAIN SIZE DISTRIBUTION SHAPE OF PARTICLES SURFACE IMPURITIES TEMPERATURE
GRAIN SIZE DISTRIBUTION SHAPE OF PARTICLES SURFACE IMPURITIES TEMPERATURE
00,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
0,3 0,4 0,5 0,6 0,7 0,8 0,9Aw
W
a
t
e
r
c
o
n
t
e
n
t
(
g
/
K
g
M
.
S
.
)
< 250 m 400-500 m 500-800 m > 800 m
< 250 mFraction 250-400 m
> 800 m
CRYSTAL SIZE DISTRIBUTIONCRYSTAL SIZE DISTRIBUTION
CRYSTAL SHAPE : Amorphous sucroseCRYSTAL SHAPE : Amorphous sucrose
Roth D. (1976) Roth D. (1976)
Sugar crystals (< 100 m) (sugar dust from factory)SugarSugar crystalscrystals (< 100 m) ((< 100 m) (sugar dust from factorysugar dust from factory))
single single crystalscrystals (< 100 m) (B.S. patent)(< 100 m) (B.S. patent)
CRYSTAL SHAPE : CRYSTAL SHAPE :
CRYSTAL SHAPE : CRYSTAL SHAPE :
0
0.05
0.1
0.15
0.2
0.25
0.3
50 60 70 80 90 100HRE %
T
e
n
e
u
r
e
n
e
a
u
(
g
/
1
0
0
g
M
.
S
.
)
sucre Rfrence microcristaux(< 250 m) < 250 m (sucre standard)
0
0.05
0.1
0.15
0.2
0.25
0.3
50 60 70 80 90 100HRE %
T
e
n
e
u
r
e
n
e
a
u
(
g
/
1
0
0
g
M
.
S
.
)
sucre Rfrence microcristaux(< 250 m) 21% de broys
70% de broys < 250 m (sucre standard)
21 %Milled
70 %
Single crystals
Manufactory crystals
SURFACE IMPURITIES(Alcaline cations in crystallization medium)
SURFACE IMPURITIES(Alcaline cations in crystallization medium)
0,000
0,050
0,100
0,150
0,200
0,250
0,300
0,350
0,400
0,450
0,500
0 20 40 60 80 100 120 140
Temps (heures)
Q
u
a
n
t
i
t
d
'
e
a
u
a
d
s
o
r
b
e
g
%
g
M
.
S
.
A =0.013%
REF =0%
B =0.033%
D=0.1%
C=0.066%
Increased surfactant
DecreasedAdsorption
SURFACE IMPURITIES(Surfactants in crystallization medium)
SURFACE IMPURITIES(Surfactants in crystallization medium)
CONTROL OF
FLOWABILITY
CONTROL OF
FLOWABILITY
010
20
30
40
50
60
70
80
90
100
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Aw
A
n
g
l
e
d
e
f
r
i
a
b
i
l
i
t
< 0 ,25mm 0,40mm< < 0 ,50mm 0,50mm< < 0 ,80 mm > 0 ,80 mm
>800m0.5
PRINCIPLES OF JENIKE CELLPRINCIPLES OF JENIKE CELL
A : surface sheared
Consolidated powder
Normal Stress
N
Shear Stress
Fc (kPa)
c (kPa)
i
Teunou et al. (1999)
ESTIMATION OF FLOWABILITY(food powder)
ESTIMATION OF FLOWABILITY(food powder)
Effet de la granulomtrie sur la prise en masse du sucre
Effet de la granulomtrie sur la prise en masse du sucre
0.000
1.000
2.000
3.000
4.000
5.000
6.000
7.000
8.000
9.000
10.000
0.000 10.000 20.000 30.000 40.000 50.000 60.000 70.000 80.000 90.000 100.000
sigma c (kPa)
F
c
(
k
P
a
)
100
00,05
0,1
0,15
0,2
0,25
0,3
grain size m
s
l
o
p
e
i
Pente i 0,0326 0,0412 0,0417 0,0568 0,0708 0,1087 0,154 0,1441 0,2653
> 1000 800
10C
35C
EFFECT OF TEMPERATURE ON ISOTHERMS
(Crystalline sugar)
EFFECT OF TEMPERATURE ON ISOTHERMS
(Crystalline sugar)
EFFECT OF TEMPERATURE ON ISOTHERMS
(Crystalline sugar)
EFFECT OF TEMPERATURE ON ISOTHERMS
(Crystalline sugar)
dp T = 9C (T = 1C)dp T =13.5C (= 1.5)
Tdp = 18C(= 2)Tdp = 23C (=2)
Tdp= 27C(=3)Tdp =31C(=4 )
Bulkflow Heat ExchangerBulkflow Heat Exchanger
IndirectCooling of food powder
No effectof air
EFFECT OF THE GLASS TRANSITIONEFFECT OF THE GLASS TRANSITION
DECAKING
PROCEDURE
DECAKING
PROCEDURE
Vaprization ofwater Dry air
P
(1)
(2)1
(3)
(4)
(5)
PILOT SILOPILOT SILO
Rate of water removal > rate of recristallization of sucroseRate of water removal > rate of recristallization of sucrose
Caked, Shear stress = 83 kPa
ERH = 55%, t = 5h
ERH = 20%,, t= 5 hRESULT =CAKEDShear stress = 12
Rate of water removal rate of recrystallizationRate of water removal rate of recrystallization
Caked, Shear stress = 85 kPa
ERH = 55%
ERH = 50 %
ERH = 40 %RESULT =DECAKEDShear stress = 7
MORPHOLOGY OF SOME DECAKED CRYSTALS
MORPHOLOGY OF SOME DECAKED CRYSTALS
SORPTION ISOTHERMSSORPTION ISOTHERMS
0
0,05
0,1
0,15
0,2
0,25
0,3
0 20 40 60 80 100HRE %
T
e
n
e
u
r
e
n
e
a
u
(
g
%
g
M
.
S
.
)
Sucre microcristallin < 250 m sucre microcristallin mott < 250 m
Single crystals
Single crystals Caked
01
2
3
4
5
6
7
0 5 10 15 20 25Temps (h)
W
a
t
e
r
c
o
n
t
e
n
t
(
g
/
1
0
0
g
M
.
S
.
) Caked sugarCaked sugardecaked sugar
Reference
KINETICS OF ADSORPTIONKINETICS OF ADSORPTION
MECHANISM OF ACTION OFANTICAKING AGENTS
Properties Action- Porous hydrophilic preferential capillary -
adsorption-------------------------------------------------------------------------- fine particles hydrophobic surface physical barrier
(silicon dioxide) inhibiting crystal growth--------------------------------------------------------------------------- HMW hydrophilic increasing Tg
(maltodextrins) antiplasticising effect--------------------------------------------------------------------------- Hydrophobic Moisture protective barrier
(lipids) spread on the surface
Properties Action- Porous hydrophilic preferential capillary -
adsorption-------------------------------------------------------------------------- fine particles hydrophobic surface physical barrier
(silicon dioxide) inhibiting crystal growth--------------------------------------------------------------------------- HMW hydrophilic increasing Tg
(maltodextrins) antiplasticising effect--------------------------------------------------------------------------- Hydrophobic Moisture protective barrier
(lipids) spread on the surface
SORPTION ISOTHERM OF MIXTURE OF POWDERS
SORPTION ISOTHERM OF SORPTION ISOTHERM OF MIXTURE OF POWDERSMIXTURE OF POWDERS
Salwyn and Slawson, 1959
Mixture of powders A and B with different hygroscopicities
CONCLUSIONCONCLUSION
Conditions of flow stability of food powders :- crystals with large size, regular shape
- homogeneous size distribution
- No amorphous or fine particles
Control and prevention of Caking :- Water vapor sorption isotherm
- flow index from shear stress slope, i
- Transition temperatue, Dew point temperatue
- Controlled humidification and dehydration
- Addition of anti-caking agent
Conditions of flow stability of food powders :- crystals with large size, regular shape
- homogeneous size distribution
- No amorphous or fine particles
Control and prevention of Caking :- Water vapor sorption isotherm
- flow index from shear stress slope, i
- Transition temperatue, Dew point temperatue
- Controlled humidification and dehydration
- Addition of anti-caking agent