Milk fat crystal networks formed under shear
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Milk fat crystal networks formed under shear Crystallisation of milk fat/sunflower oil blends: kinetics and reological properties t Vanhoutte, Imogen Foubert, André Huyghebaert and Koen Dewet artment of food science and nutrition nt University, Belgium
description
Milk fat crystal networks formed under shear. Bert Vanhoutte, Imogen Foubert, André Huyghebaert and Koen Dewettink Department of food science and nutrition Ghent University, Belgium. Crystallisation of milk fat/sunflower oil blends: kinetics and reological properties. Microstructure. - PowerPoint PPT Presentation
Transcript of Milk fat crystal networks formed under shear
Milk fat crystal networks formed under shear
Crystallisation of milk fat/sunflower oil blends: kinetics
and reological properties
Bert Vanhoutte, Imogen Foubert, André Huyghebaert and Koen DewettinkDepartment of food science and nutritionGhent University, Belgium
Microstructure
Fat crystal habit, size, distribution
Lipid-composition
Polymorphism, polytypism
Spatial distribution of fat crystals
Macroscopic properties
processing
Source: Marangoni&Hartel, Food Technology, 1998
supersaturating
nucleationcrystal growth
crystal size distribution
fraction solid fat
aggregation
gelation
strong network forming
post- and recrystallisationV
an d
er W
aals
fo
rces
sint
erin
g
pro c
essi
n gst
o ra g
e
stru
ctur
e
Source: PhD Thesis William Kloek
Crystallisation under shearAgitation rate 50, 100, 200 and 300rpmTemperature recordingSFC measurementsCrystallisation interrupted at 75% of equilibriumSamples for rheological tests and microscopic analysis
20mm
15mm
70mm
85mm
20mm
Temperaturerecording
20mm
15mm
70mm
85mm
20mm
Temperaturerecording
Rheological measurements
25mm2,5mm
25mm2,5mm
Polarised microscopyMicrostructure formation in tubs not under microscopic slides2D images of microstructure by cryotomographyParticle size measurements of primary crystal aggregates with a gridNO Quantitative analysis of spatial distribution
Processing conditionsTemperature of the coolant 21 and 26.5°CAgitation rate 50-100-200-300rpmFive blends High melting fraction milk fat (HMF) – Sunflower Oil (SFO) 60/40, 70/30, 80/20, 90/10 and 100/0
Multiple effect of agitationEffect on the cooling rateConvective heat transfer coefficient
Effect on the mass transferShear rate
).(... wcshcs
p TTFtTcm
Convective heat transfer coefficient (assumption temperature perfectly homogeneous in
vessel)
Shear rate (calculated at the tip of the impeller compared to the
vessel wall)
Processing
Crystallisation kinetics
Convective heat transfer h
Shear rate
emperature of the coolant
Lipid composition
Supercooling
Supersaturation
Induction time
Growth rate
?
Qualitative analysis
202530354045505560
0 10 20 30 40
Time (min)
T (°
C)
50100200300
2025
303540
4550
5560
0 10 20 30 40Time (min)
T (°
C)
50100200300
2025
30
3540
4550
5560
0 10 20 30 40Time (min)
T (°
C)
50100200300
20
25
303540
45
50
5560
0 10 20 30 40Time (min)
T (°
C)
50100200300
(60/40)21°C
(60/40)26.5°C
(100/0)21°C
(100/0)26.5°C
Anova on the induction time
Enter method
Stepwise method
Conclusion:The induction time is affected by agitation but mainly by an increase in heat transfer rather then an effect of mass transfer
Anova on the growth rateEnter method
Stepwise method
ConclusionThe growth rate is influenced by shear rate rather than by the convective heat transfer coefficient, which suggest the growth rate is more affected by the mass transfer than by the overall release of heat towards the coolant
Microstructure
0
100
200
300
400
500
600
50 100 200 300
agitation rate (rpm)
crys
tal a
ggre
gate
siz
e (µ
m)
21°C26,5°C
0
100
200
300
400
500
600
50 100 200 300
agitation rate (rpm)
crys
tal a
ggre
gate
siz
e (µ
m)
21°C26,5°C
0
100
200
300
400
500
600
50 100 200 300agitation rate (rpm)
crys
tal a
ggre
gate
siz
e (µ
m)
21°C26,5°C
0
100
200
300
400
500
600
50 100 200 300
agitation speed (rpm)
crys
tal a
ggre
gate
siz
e (µ
m)
21°C26,5°C
Anova on primary crystal aggregates
Size decreases with temperature of the coolant and more agitationNo effect on the lipid compositionEffect of agitation = effect on primary or secondary nucleation???
Effect on shear on crystalsHigh shear Low shear
+/- homogeneous size distribution
More heterogenous size distribution
Post crystallisationDepends on: The difference between crystallisation
temperature and the storage temperatureVan der Waals – Solid bridgesThe cooling rateThe specific surface area
Anova Rheology
Power-law modelsRelation between SFC and G’ can be described by power-law models
where A is the interaction parameter and µ is the scaling exponent
Fractal nature of fat crystal networksApplicable on this system?
µSFCAG '
DdSFCG 1
'
Regression analysisThe effect of agitation is larger when the degree of post-crystallisation is smallLonger storage leads to space filling of initial pores
-8
-6
-4
-2
0
2
4
6
8
0 50 100 150 200 250 300 350
agitation rate (rpm)
Log
A
Tw=21°CTw=26,5°C
The interaction term A
The scaling exponent µ
0
1
2
3
4
5
6
7
8
9
0 50 100 150 200 250 300 350
agitation rate (rpm)
scal
ing
expo
nent
(µ)
Tw=21°CTw=26,5°C
Relation between process parameters, crystallisation
kinetics and rheological properties
T=low + shear=low T=high + shear=low
T=low + shear=high T=high + shear=high
Lipid composition
Crystallisation kinetics
Primary crystal aggregates
Final microstructure
Rheological properties
Temperature of the coolant
AgitationShear rate
Heat transfer
Storage temperature
AcknowledgementsIWT (Institute for the Promotion of Innovation by Science and Technology in Flanders)Aveve Dairy products, BelgiumSpecial thanks to Wouter Pillaert, Brecht Vanlerberghe, Leo Faes and Frank Duplacie
