Dewettinck, Koen

Foubert, Imogen

Keersebilck, Thijs

Vanrolleghem, Peter

English

Ghent University Academic Bibliography

WHAT IS THE EFFECT OF THE SAMPLE PREPARATION METHOD?Method A: sampling with material cleaned with ethanol in oven at 60°C for 15 min transfer to DSC pan with plastic micropipetteMethod B: use of desiccator for equilibration to room temperature sampling with material cleaned with acetone in oven at 60°C for 15 min transfer to DSC pan with hot, glass Pasteur pipetteRESULT: Significant differences on a parameters of Gompertz and Avrami modelλ parameter of Gompertz modelk parameter of Avrami modelDifferential scanning calorimetry to measurethe isothermal crystallization kinetics of cocoa butterImogen Foubert 1; Peter A. Vanrolleghem2; Thijs Keersebilck1  and Koen Dewettinck11Department of Food Technology and Nutrition, Faculty of Agricultural and Applied Biological Sciences, Ghent University, Coupure Links 653, B-9000 Gent, Belgium2BIOMATH, Faculty of Agricultural and Applied Biological Sciences, Ghent University, Coupure Links 653, B-9000 Gent, BelgiumE-mail: imogen.foubert@rug.ac.be, Tel. +32 9 2646163 Fax : +32 9 264 621801020304050600 0,5 1 1,5 2 2,5Time / hHeat released (J/g)65°C / 15 min65°C / 30 min80°C / 15 minCONCLUSIONS• Use of new time determination algorithm leads to objective determination of start and end point of integration• Sample preparation method has to be kept constant to eliminate influence thereof• 65°C for 15 min is enough to eliminate any memory effectAcknowledgementsImogen Foubert is a research assistent of the Fund for ScientificResearch – Flanders (F.W.O. – Vlaanderen).Barry-Callebaut, Wieze, Belgium is acknowledged forproviding the cocoa butter.Dr. ir. Olivier Thas is acknowledged for the help with thestatistics.00,010,020,030,040 1 2 3Time (h)Heat flow (W/g)0204060800 1 2 3Time (h)Heat released (J/g)STEP 1:PREPARATION OF DSC SAMPLESTEP 2: DSC RUNTime – temperature program:• melting the sample to eliminate memory effect• cooling at 8°C /min to crystallization temperature (17.2°C)• keep at that temperature until crystallization iscompleteSTEP 3: INTEGRATIONKnowledge of t0 and te is necessary !!STEP 4:MODELING WITHAVRAMI AND GOMPERTZ MODEL( ) 1***)(+−−=taeeeatfλµf(t): amount of crystallization at time t [J/g]a: value for f as t approaches infinity[J/g]k: crystallization rate constant [h-n]n: Avrami exponent  [-]f(t): amount of crystallization at time t[J/g]a: value for f as t approaches infinity[J/g]µ: maximum increase rate [J/g h-1]λ: induction time [h]WHAT IS THE EFFECT OF THE MELTINGPROTOCOL?Comparison of three melting protocols:65°C for 15 minutes65°C for 30 minutes80°C for 15 minutesRESULT : No significant differences between the threemelting protocols on the Avrami and Gompertz parametersHOW TO DETERMINE t0 AND te?Suggested method in literature is by visual inspectionAt the authors’ laboratory eight persons were asked tovisually determine the start and end point of a DSC curve:New objective calculation algorithmfor t0 and teNote:dQ/dtf = final heat flow value =median of last five valuesσ = baseline noise0102030405060700 0,5 1 1,5 2 2,5Time (h)Heat released (J/g)Method AMethod BOperator Start point (min) End point (min)1 37.98 119.042 40.18 130.263 39.51 111.174 39.91 94.495 40.01 112.086 41.84 100.297 41.95 109.958 37.99 109.07Mean 40 110Standard deviation 1 11Coefficient of variation (%) 3.7 9.8Via new algorithm (see right) 37 123( )ntkeatf *1*)( −−=AVRAMI GOMPERTZNEW OBJECTIVE TIMEDETERMINATIONALGORITHMPreparation stepDetermination ofslope of curveDetermination ofsign changes(n1, n2, …)Determination of t0npeak = 2? t0 = n1t0 = n neg.-pos. ofwhich heat flowvalue is lowestDetermination of tedetermination ofdQ/dtf|dQ/dt npeak+1 – dQ/dtf|<3σte = n peak+3|dQ/dt n peak+2 – dQ/dtf|<3σte = n peak+1+3noyesyesnoyesetc.X Xt0 t te∆Ht∆Ht0 t te∆Ht∆HInfluence of melting protocol on crystallizationInfluence of sample preparation method on crystallizationLARGE VARIABILITY!!

Differential scanning calorimetry to measure the isothermal crystallization kinetics of cocoa butter

https://biblio.ugent.be/publication/307534/file/8721669.pdf

Differential scanning calorimetry to measure the isothermal crystallization kinetics of cocoa butter

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