the effect of lecithin and sorbitan tristearate on the crystallisation kinetics of a confectionery...

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