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Milk fat crystal networks formed under shear

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.

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Milk fat crystal networks formed under shear

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  1. 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

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

  3. supersaturating nucleation crystalgrowth crystal size distribution structure processing fraction solid fat aggregation Van der Waals forces gelation strong network forming sintering storage post- and recrystallisation 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. ? Lipid composition Crystallisation kinetics Supercooling Supersaturation Induction time Growth rate Processing Convective heat transfer ah Shear rate g° Temperature of the coolant

  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 Low shear High 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=low T=high + shear=low T=low + shear=high T=high + shear=high

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

  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

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