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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 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 Peak times are dependent on both STS and lecithin
Enthalpy of crystallisation 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
Deconvolution of DSC peaks STS Lecithin
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 In original Avrami equation coefficients k2 and n2 are zero and is 100%
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