1. 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 Dewettink Department of food science and nutrition Ghent University, Belgium

2. Microstructure Fat crystal habit, size, distribution Lipid-composition Polymorphism, polytypism Spatial distribution of fat crystals Macroscopic properties processing Source: Marangoni&Hartel, Food Technology, 1998

3. supersaturating nucleation crystal growth crystal size distribution fraction solid fat aggregation gelation strong network forming post- and recrystallisation Van der Waals forces sintering processing storage structure Source: PhD Thesis William Kloek

4. Crystallisation under shear Agitation rate 50, 100, 200 and 300rpm Temperature recording SFC measurements Crystallisation interrupted at 75% of equilibrium Samples for rheological tests and microscopic analysis

5. Rheological measurements

6. Polarised microscopy Microstructure formation in tubs not under microscopic slides 2D images of microstructure by cryotomography Particle size measurements of primary crystal aggregates with a grid NO Quantitative analysis of spatial distribution

7. Processing conditions Temperature of the coolant 21 and 26.5°C Agitation rate 50-100-200-300rpm Five blends High melting fraction milk fat (HMF) – Sunflower Oil (SFO) 60/40, 70/30, 80/20, 90/10 and 100/0

8. Multiple effect of agitation Effect on the cooling rate Convective heat transfer coefficient Effect on the mass transfer Shear rate

9. Convective heat transfer coefficient (assumption temperature perfectly homogeneous in vessel) Shear rate (calculated at the tip of the impeller compared to the vessel wall)

10. Processing Crystallisation kinetics Convective heat transfer  h Shear rate   emperature of the coolant Lipid composition Supercooling Supersaturation Induction time Growth rate ?

11. Qualitative analysis (60/40) 21°C (60/40) 26.5°C (100/0) 21°C (100/0) 26.5°C

12. Anova on the induction time Enter method Stepwise method

13. Conclusion: The induction time is affected by agitation but mainly by an increase in heat transfer rather then an effect of mass transfer

14. Anova on the growth rate Enter method Stepwise method

15. Conclusion The 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

16. Microstructure

17. Anova on primary crystal aggregates Size decreases with temperature of the coolant and more agitation No effect on the lipid composition Effect of agitation = effect on primary or secondary nucleation???

18. Effect on shear on crystals High shear Low shear +/- homogeneous size distribution More heterogenous size distribution

19. Post crystallisation Depends on: The difference between crystallisation temperature and the storage temperature Van der Waals – Solid bridges The cooling rate The specific surface area

20. Anova Rheology

21. Power-law models Relation 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 networks Applicable on this system?

22. Regression analysis The effect of agitation is larger when the degree of post-crystallisation is small Longer storage leads to space filling of initial pores

23. The interaction term A

24. The scaling exponent µ

25. Relation between process parameters, crystallisation kinetics and rheological properties

26. T=low + shear=lowT=high + shear=low T=low + shear=highT=high + shear=high

27. Lipid composition Crystallisation kinetics Primary crystal aggregates Final microstructure Rheological properties Temperature of the coolant Agitation Shear rate Heat transfer Storage temperature

28. Acknowledgements IWT (Institute for the Promotion of Innovation by Science and Technology in Flanders) Aveve Dairy products, Belgium Special thanks to Wouter Pillaert, Brecht Vanlerberghe, Leo Faes and Frank Duplacie