Physical properties and crystallization kinetics of bulk and emulsified triglycerides.

摘要

The processing and storage stability of emulsified triglycerides is closely related to the crystallization properties of the dispersed phase. The effect of two valve homogenization treatments (800/600 and 2500/600 psi) on the physical properties and crystallization kinetics of two oil-in-water (40%) emulsions (palm stearine/canola oil (PSCO) blend and lard) was determined. Bulk and emulsified fats were characterized by solid fat content (SFC), polymorphic behaviour, free energy of nucleation and nucleation kinetics. The SFC of the emulsified fats was more strongly affected by temperature than the bulk fats, observed as a higher rate of maximum SFC increase as a function of decreasing temperature. The 2500 psi lard treatment had a significant decrease in final SFC relative to the bulk (P 0.05). The α, β′ and β polymorphs were observed in both fat systems using differential scanning calorimetry and powder x-ray diffraction. X-ray analysis of the bulk fats showed 2L long spacings in both fats and 3L long spacings in lard. Bulk and emulsified fat crystallization was modelled using the Avrami equation yielding Avrami indices (n) less than one between 15 and 25°C, suggesting instantaneous nucleation. Homogeneous and heterogeneous models were fitted to the crystallization curves of the emulsified fats; the homogeneous model was found to fit the curves significantly better (P 0.05). No significant difference was found when the crystallization data of the emulsified fats was fitted for surface and volume nucleation (P > 0.05) mechanisms.