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

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

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

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  1. The effect of lecithin and sorbitan tristearate on the crystallisation kinetics of a confectionery fat Jari Alander & Yvonne Samuelsson Karlshamns AB, R&D

  2. 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

  3. Materials & methods • Hydrogenated confectionery fat • C16:0 11%, C18:0 12%, C18:1 70% (c+t) • Soybean lecithin • Sorbitan tristearate (STS)

  4. 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

  5. Isothermal crystallisation by DSC • Original curve with three evaluation methods • Peak time / integral • Deconvolution • Avrami modelling of conversion curves

  6. 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

  7. Peak times Peak times are dependent on both STS and lecithin

  8. Enthalpy of crystallisation The crystallisation enthalpy is mainly determined by STS concentration

  9. 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

  10. Deconvolution of DSC peaks STS Lecithin

  11. 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 ?

  12. Avrami vs extended Avrami equations In original Avrami equation coefficients k2 and n2 are zero and  is 100%

  13. Extended Avrami modelling of crystallisation curves

  14. 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

  15. 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

  16. 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

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