Catalytic Impurities, Habit Catalytic Impurities, Habit Modification and Crystal Modification and Crystal

Structure in FatsStructure in Fats

Lipid Structural Properties Lipid Structural Properties Symposium, Unilever Research, Symposium, Unilever Research,

Colworth, 2002Colworth, 2002Malcolm PoveyMalcolm Povey

University of LeedsUniversity of Leeds

CollaboratorsCollaborators

Scott Hindle – University of LeedsScott Hindle – University of Leeds Paul Smith – Unilever and SIKPaul Smith – Unilever and SIK Kevin Smith – Unilever ColworthKevin Smith – Unilever Colworth

The Importance of Catalytic The Importance of Catalytic ImpuritiesImpurities

They are generally essential to They are generally essential to crystallization – homogeneous crystallization – homogeneous nucleation is very rare in oilsnucleation is very rare in oils

The physics of crystal nucleation is The physics of crystal nucleation is very different to that of crystal very different to that of crystal growth. So an effective catalyser can growth. So an effective catalyser can also poison the growth of individual also poison the growth of individual crystal faces, dramatically altering crystal faces, dramatically altering crystal morphology and even prevent crystal morphology and even prevent growth altogether.growth altogether.

Quantifying crystal nucleationQuantifying crystal nucleation

Determine the rate of increase of Determine the rate of increase of crystal material at constant crystal material at constant undercoolingundercooling

Use ultrasound velocity to determine Use ultrasound velocity to determine crystal solidscrystal solids

Obtain Gibbs free energy, upper limit Obtain Gibbs free energy, upper limit for critical nucleus size, for critical nucleus size,

The emulsion crystallization The emulsion crystallization techniquetechnique

There are great advantages to dispersing There are great advantages to dispersing material as an emulsion in a non-crystallizing material as an emulsion in a non-crystallizing continuous phase in order to study crystal continuous phase in order to study crystal nucleation. nucleation.

It permits the use of the very accurate and It permits the use of the very accurate and convenient ultrasound technique for the convenient ultrasound technique for the determination of the low quantity of solids determination of the low quantity of solids evident during the initial stages of nucleation. evident during the initial stages of nucleation.

The concentration of nuclei may be controlled The concentration of nuclei may be controlled through droplet size. through droplet size.

Isothermal crystallization studies may be Isothermal crystallization studies may be conveniently carried out this way, permitting the conveniently carried out this way, permitting the identification of nuclei, through the direct identification of nuclei, through the direct determination of the bulk melting point.determination of the bulk melting point.

Determining catalytic impuritiesDetermining catalytic impurities Emulsify oil as a hot oil-in-water emulsion in which Emulsify oil as a hot oil-in-water emulsion in which

all components of the oil are liquid.all components of the oil are liquid. Measure psd (Light scattering - dilute and Measure psd (Light scattering - dilute and

ultrasound scattering - concentrated)ultrasound scattering - concentrated) Crash cool to a given undercooling at which the Crash cool to a given undercooling at which the

rate of crystallization is appropriate for our rate of crystallization is appropriate for our measurement techniquemeasurement technique

Measure the temporal evolution of crystal solids at Measure the temporal evolution of crystal solids at constant temperature. Repeat at 4 other constant temperature. Repeat at 4 other undercooling.undercooling.

Find the best fit model (Homogeneous, Find the best fit model (Homogeneous, heterogeneous, surface, volume – 4 models in all) heterogeneous, surface, volume – 4 models in all) using psd. Determine using psd. Determine JJ, , nn, , GG and and dd5050

1450

1500

0 5 10 15 20 25Temperature (°C)

Vel

ocity

(m

/s)

Tween 20

Sodium caseinatePlot of ultrasonic velocity Plot of ultrasonic velocity against temperature for against temperature for 20.75% (v/v) WACB-in-water 20.75% (v/v) WACB-in-water emulsions (0.8% Tween 20 and emulsions (0.8% Tween 20 and 1.0% sodium caseinate) cooled 1.0% sodium caseinate) cooled at 5°C/hour.at 5°C/hour.

Plot of solids against Plot of solids against temperature for 20.75% (v/v) temperature for 20.75% (v/v) WACB-in- water emulsions WACB-in- water emulsions cooled at 5°C/hour (0.8% cooled at 5°C/hour (0.8% Tween 20 & 1.0% sodium Tween 20 & 1.0% sodium caseinate).caseinate).

0

0.2

0.4

0.6

0.8

1

6 8 10 12 14 16Temperature (°C)

Sol

ids

Sodium caseinate

Tween 20

Plot of solids against time for 20.75% (v/v) WACB-in-water emulsions (0.8% Tween 20) crystallised isothermally at 14.2, 15.0, 15.5 and 15.8°C. Heterogeneous volume particle size distribution models are fitted.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 50 100 150Time (minutes)

Sol

ids

14.2°CHet vol psd model15.0°CHet vol psd model15.5°CHet vol psd model15.8°CHet vol psd model

Plot of solids against time for 20.75% (v/v) WACB-in-water emulsions (0.8% Tween 20) crystallised isothermally at 14.2, 15.0, 15.5 and 15.8°C. Heterogeneous volume particle size distribution models are fitted

0

0.1

0.2

0.3

0 2 4 6 8 10Time (minutes)

So

lids

14.2°CHet vol psd model15.0°CHet vol psd model15.5°CHet vol psd model15.8°CHet vol psd model

Characterising catalytic impuritiesCharacterising catalytic impurities

Determine Determine the the temperature temperature dependence dependence of the of the concentration concentration of catalytic of catalytic impuritiesimpurities

y = -0.6791x + 27.127

R2 = 0.9631

16

16.5

17

17.5

18

14 14.5 15 15.5 16

Isothermal temperature (°C)lo

g10 N

imp

(m

-3)

y = -0.1334x + 40.054

R2 = 0.951

36

36.5

37

37.5

38

38.5

39

12 14 16 18 20 22 24 26

Supercooling term (10-5 K-3)

lnJ

o (

m-3

s-1)

Cocoa butter seed crystalsCocoa butter seed crystals There are few seed crystals whose size There are few seed crystals whose size

exceeds 0.28 exceeds 0.28 m at 80 m at 80 C. C. From our isothermal crystallization From our isothermal crystallization

experiments, with between 3 x 10experiments, with between 3 x 101616 and 3 x and 3 x 10101717 seed crystals per m seed crystals per m33 of cocoa butter, of cocoa butter, we infer their average size to be less than we infer their average size to be less than 0.09 0.09 m. m.

The melting point of the nucleating layer in The melting point of the nucleating layer in the seed crystal is 14 the seed crystal is 14 ooC.C.

There is strong evidence from X-ray There is strong evidence from X-ray diffraction that it is the alpha form of POS diffraction that it is the alpha form of POS that comprises the nucleating layer in the that comprises the nucleating layer in the seed crystal.seed crystal.

Characterising surfactantCharacterising surfactant

ks T d32 n0 nc nc/n0 1/w E/kbT 10-6 s-1 K Pa s μm 1020 m-3 1020 s-1 m-3 s-1 μs

0.5 wt % beta casein51

0.18 279.2 0.2 0.007 0.4 0.0597 0.523 9 0.0205 17.70

0.9 wt % beta lactoglobulin51

0.66 279.2 0.2 0.007 0.36 0.0819 0.984 12 0.0549 16.72

0.65 wt % SDS51

1.30 279.2 0.2 0.007 0.36 0.0819 0.984 12 0.108 16.04

0.8 wt % Tween 2099

100 288.2 0.2075 0.007 0.26 7.21 7880 1093 0.0915 16.21

0.94 wt % Tween 2087

1.7 277.2 0.125 0.007 0.37 0.0471 0.324 7 0.247 15.21

1.55 wt Tween 2087

3.10 277.2 0.125 0.007 0.37 0.0471 0.324 7 0.451 14.61

2 wt % Tween 2050

2.42 279.2 0.2 0.007 0.36 0.0819 0.984 12 0.185 15.50

2.16 wt Tween 2087

5.20 277.2 0.125 0.007 0.37 0.0471 0.324 7 0.757 14.09

3.07 wt Tween 2087

7.40 277.2 0.125 0.007 0.37 0.0471 0.324 7 1.08 13.74

5.23 wt Tween 2087

8.10 277.2 0.125 0.007 0.37 0.0471 0.324 7 1.18 13.65

7.07 wt Tween 2087

9.20 277.2 0.125 0.007 0.37 0.0471 0.324 7 1.34 13.52

2 wt % Tween 20 +0.3 wt % xanthan22

1.80 279.2 0.2 0.1 0.37 0.0754 0.0584 1 2.32 12.97

Crystal growth and catalytic Crystal growth and catalytic impuritiesimpurities

Paul Smith, “The Paul Smith, “The molecular basis for molecular basis for crystal habit crystal habit modification in modification in tryglycerides”, tryglycerides”, University of Leeds University of Leeds Thesis, 1995Thesis, 1995

Chain length Chain length matchingmatching

TrilaurinTrilaurin

Trilaurin, catalytic impurities and Trilaurin, catalytic impurities and chain length matchingchain length matching

Trilaurin crystal growthTrilaurin crystal growth

ConclusionsConclusions

Catalytic impurities play a role both Catalytic impurities play a role both during nucleation and during crystal during nucleation and during crystal growthgrowth

Catalytic impurities may both catalyse Catalytic impurities may both catalyse nucleation and prevent crystal growth nucleation and prevent crystal growth of one or more crystal facetsof one or more crystal facets

Identification of catalytic impurities is Identification of catalytic impurities is one of the most important outstanding one of the most important outstanding issues in crystallisationissues in crystallisation

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Fundamentals of Formulation" - RSC Special Publication Number 258 eds Eric Dickinson and Reinhard Fundamentals of Formulation" - RSC Special Publication Number 258 eds Eric Dickinson and Reinhard Miller, pp 152 -162Miller, pp 152 -162

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Hindle, S., Povey, M. J. W. and Smith, K. (2000), Kinetics of Crystallization in Polydisperse n-Hindle, S., Povey, M. J. W. and Smith, K. (2000), Kinetics of Crystallization in Polydisperse n-hexadecane and Cocoa Butter Emulsions Accounting for Droplet Collision-Mediated Nucleation, hexadecane and Cocoa Butter Emulsions Accounting for Droplet Collision-Mediated Nucleation, J. Coll. J. Coll. Interface Sci. Interface Sci. 232232, 370-380, 370-380

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Dickinson, E., Ma, J., and Povey, M. J. W. (1996), Crystallization Kinetics in Oil-In-Water Emulsions Dickinson, E., Ma, J., and Povey, M. J. W. (1996), Crystallization Kinetics in Oil-In-Water Emulsions Containing a Mixture of Solid and Liquid Droplets,Containing a Mixture of Solid and Liquid Droplets, J. Chem. Soc. -Faraday Trans. I J. Chem. Soc. -Faraday Trans. I 9292, 1213-1215, 1213-1215

Smith, P. R., Povey, M. J. W., and Cebula, D. J. (1994), The Application of Temperature Gradient Smith, P. R., Povey, M. J. W., and Cebula, D. J. (1994), The Application of Temperature Gradient Microscopy Techniques to Trilaurin Crystallisation,Microscopy Techniques to Trilaurin Crystallisation, Crystallisation and crystal growth: An Crystallisation and crystal growth: An interdisciplinary perspective.interdisciplinary perspective.

Smith, P. R., Cebula, D. J., and Povey, M. J. W. (1994), The Effect of Lauric-Based Molecules on Trilaurin Smith, P. R., Cebula, D. J., and Povey, M. J. W. (1994), The Effect of Lauric-Based Molecules on Trilaurin Crystallization, Crystallization, J. Am. Oil. Chem. Soc. J. Am. Oil. Chem. Soc. 7171, 1367-1372, 1367-1372

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Coupland, J., Dickinson, E., McClements, D. J., Povey, M. J. W., and de Rancourt de Mimmerand, C. Coupland, J., Dickinson, E., McClements, D. J., Povey, M. J. W., and de Rancourt de Mimmerand, C. (1993), Crystallisation in Simple Paraffins and Monoacid Saturated Triacylglycerols Dispersed in Water, (1993), Crystallisation in Simple Paraffins and Monoacid Saturated Triacylglycerols Dispersed in Water, Food Colloids and Polymers: Stability and Mechanisms, RSCFood Colloids and Polymers: Stability and Mechanisms, RSC

Cebula, D. J., McClements, D. J., Povey, M. J. W., and Smith, P. R. (1992), Neutron Diffraction Studies of Cebula, D. J., McClements, D. J., Povey, M. J. W., and Smith, P. R. (1992), Neutron Diffraction Studies of Liquid and Crystalline Trilaurin, J. Am. Oil. Chem. Soc. Liquid and Crystalline Trilaurin, J. Am. Oil. Chem. Soc. 6969, 130-136, 130-136

Smith, PR (1997) The Molecular Basis for Crystal Habit Modification, PhD Thesis, University of LeedsSmith, PR (1997) The Molecular Basis for Crystal Habit Modification, PhD Thesis, University of Leeds Hindle, SA (2000) Investigation of Cocoa Butter Crystallization Using Ultrasound Velocity Hindle, SA (2000) Investigation of Cocoa Butter Crystallization Using Ultrasound Velocity

Measurements, PhD Thesis, University of LeedsMeasurements, PhD Thesis, University of Leeds