Nacl

WATER VAPOR SORPTION

ISOTHERMS AND THE

CAKING OF FOOD POWDERS


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


ISOTHERMS


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


Solid

Air

Liquid

75% < HRE < 85%75% < HRE < 85%

Solid bridge

Capillary stepCapillary step


Solid

Syrup

500 m

HRE> 85 %HRE> 85 %

Syrup surrounding crystalsSyrup surrounding crystals

SolidLiquid

Drop stepDrop step


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)


(Crystalline sugar)


(Crystalline sugar)


(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

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