the effect of lecithin and sorbitan tristearate on the crystallisation kinetics of a confectionery...
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The effect of lecithin and sorbitan tristearate on the crystallisation kinetics of a
confectionery fat
Jari Alander &Yvonne Samuelsson
Karlshamns AB, R&D
Introduction
• Polymorphism and crystallisation kinetics of fats are influenced by emulsifiers– Inhibits or accelerates polymorphic
transformations– Influences nucleation and/or growth
• Few systematic studies in the presence of auxiliary food components
Materials & methods
• Hydrogenated confectionery fat– C16:0 11%, C18:0 12%, C18:1 70% (c+t)
• Soybean lecithin• Sorbitan tristearate (STS)
Materials & methods
• 70% fat, 30% sugar, 0-0.5% lecithin, 0-2% STS (w/w on fat+sugar), D-optimal experimental design with replicates
• Fat and sugar mixed, ground on three-roll refiner• Heated to 60°C, emulsifiers added, equilibrated
at 30°C• DSC (Mettler TA8000)• Isothermal at 21, 23 and 25°C after initial
melting at 80°C and cooling with 10°C/min
Isothermal crystallisation by DSC
• Original curve with three evaluation methods
• Peak time / integral• Deconvolution• Avrami modelling of
conversion curves
Results
• Peak times and crystallisation enthalpies– Evaluation of experimental design– Modelling of response surfaces
• Deconvolution of original data– Modelling of peak shape using Gaussian
peak fitting
• Kinetic modelling of conversion curves– Avrami vs extended Avrami
Peak times
Peaktime at 21 C (min) Peaktime at 23 C (min)
Peaktime at 25 C (min)
Investigation: Crystallization kinetics (PLS, comp.=3)Contour Plot
Peak times are dependent on both STS and lecithin
Enthalpy of crystallisation
T=21 C T= 23 C
T=25 C
Investigation: Crystallization kinetics (PLS, comp.=2)Contour Plot
The crystallisation enthalpy is mainly determined by STS concentration
Conclusions / peak times
• Quadratic/interaction terms gave best modelling results
• STS at low concentrations increases crystallisation rate and decreases at high concentrations
• Lecithin has smaller influence• STS has a destructurating effect (lower
enthalpies of crystallisation)• More complex models needed for
interpretation
0 600 1200 1800
0,0
0,5
1,0
1,5
2,0
N14 23 C 1 0,25
He
at f
low
(m
W)
Time (s)
0 600 1200 1800
0,0
0,5
1,0
1,5
2,0
N1 23 C 0 0
He
at f
low
(m
W)
Time (s)
0 600 1200 1800
0,0
0,5
1,0
1,5
2,0
N2 23 C 0 0,5
He
at f
low
(m
W)
Time (s)
0 600 1200 1800
0,0
0,5
1,0
1,5
2,0
N3 23 C 2 0
He
at f
low
(m
W)
Time (s)
0 600 1200 1800
0,0
0,5
1,0
1,5
2,0
N4 23C 2 0,5
He
at f
low
(m
W)
Time (s)
Lecithin
STS
Deconvolution of DSC peaks
Conclusions/deconvolution
• Three peaks needed for good modelling of peak shape
• Two major crystallisation events, one slow process common in all samples
• Fractionation or selective influence on nucleation/growth events induced by emulsifiers ?
Avrami vs extended Avrami equations
1110012
21
1
ntke
ntket
In original Avrami equation coefficients k2 and n2 are zero and is 100%
Extended Avrami modelling of crystallisation curves
Conclusions – Avrami modelling
• Traditional Avrami model does not give satisfactory fit for early or late parts for the conversion curve
• Extended Avrami model gives improved fit on entire conversion curve
• STS slows down nucleation but increases growth rate of first fraction
• Lecithin slows down both nucleation and growth
• STS overrules lecithin in combinations
Mechanistic considerations
• STS contains both polar monoesters (induces nucleation) and less polar triesters (slow down nucleation and growth)
• At low concentrations, nucleation inducing effect of more polar monoesters dominate
• At high concentrations, nucleation/growth inhibiting effect of triesters dominate
• Lecithin in absence of STS slows down both nucleation and growth
Summary
• The crystallisation of a hydrogenated confectionery fats was investigated by isothermal DSC in presence of sugar and emulsifiers
• Effects on nucleation/growth by emulsifiers were observed
• Polar/non-polar constituents of food emulsifiers may have different effects on the crystallisation behaviour