thermal analysis Flashcards
DSC measurements
◦ Tg - glass transition temperature
◦ Tm - crystalline melt temperature
◦ ΔH-enthalpy
Oils fats and spreads
onset temp of melt/crystallization/polymorphic behavior/oxidation stability
flour and rice starch
reterogradation/gelatinization/glass trasition Tg
Vegetable powders
glass transition Tg
Pates and gels containing polysaccharides or gums
specific heat cp, onset temp of melt and crystallizationp
protein
denaturation and aggregation
Protein 3 points
➢ Protein stability during denaturation as a result of thermal treatment (denaturation of protein structure).
➢ This phenomena is endothermic (observed by as endothermic peak in the DSC thermogram).
➢ Calculation of enthalpy values to obtain the thermal energy needed for protein denaturation.
starch
➢ Measures first-order (melting) and second-order (glass transition) transition temperatures.
➢ DSC gives information on transitions that occur during heating an aqueous suspension of starch granules.
➢ Native starch or modified starch can show endothermic peaks: gelatinization (50<T<80°C), amylose-lipid complex (T>100°C) or recrystalized amylose (T>140°C).
➢ Gelatinisation enthalpy (∆H) depends on changes caused by disruption of crystalline network, destruction of double helices, disturbances in amorphous phase of starch granules and changes during swelling
Oils and fats
Measures melting and crystallisation behaviour of different types of oils and fats.
▪ Fat phase transitions and melting range
▪ Oxidative stability (measure oxidation induction time, OIT)
▪ Onset temperature, heat of fusion ( H)
▪ Polymorphic behaviour and crystallization of oils and fats (α, beta’, and beta)
▪ Solid fat content (SFC) based on measurement of the fusion heat of the solid part of lipids.
▪ Contamination of lipids by determination of solid fat index (SFI)
TGA
1 volatiles (moisture, solvents, monomers)
2 polymer decomposition
3 change og atmosphere
4 burning step of carbon
5 residue (ash, fillers, glass fibers
