On the relevance of inhomogeneity in saturated fatty acid compositions for the crystallization kinetics of fat blends

Abstract

In this contribution, the crystallization kinetics of model fat blends containing trisaturated and mono-unsaturated TAGs of different saturated fatty acid composition are investigated via differential scanning calorimetry (DSC) and time-resolved small and wide angle X-ray scattering (SAXS/WAXS). The effect of inhomogeneity in saturated fatty acid composition was studied by varying between palmitic and stearic sources for trisaturated (POSt – palm stearin and FHRO – fully hydrogenated rapeseed oil) and using palm mid fraction (PMF) and shea stearin (ShSt) sources for mimicking the mono-unsaturated TAGs (PMF – palm mid fraction and ShSt – shea stearin). The kinetics were followed via SAXS/WAXS upon cooling at different rates (1 and 10 °C/min) and during the isothermal hold at 0 °C (273 K) for 60 min. The blends revealed a multiple step crystallization with co-existing polymorphic forms and a slow restructuring process. Generally, mono-unsaturated triglycerides tended to impede the polymorphic transition of the trisaturated fraction. The trisaturated triglyceride fraction formed an α phase at the beginning of the crystallization. Quickly after, co-existing β’ and β phases were recorded. In each case, the subsequent crystallization events were dictated by the mono-unsaturated fraction with ShSt affecting the crystallization more drastically than PMF. Differences were diminished when a low cooling rate was applied. Further, the low cooling rate allowed the formation of a β phase in FHRO-containing samples before an additional β’ phase was recorded. The differences in explicit fatty acid composition, TAG diversity and minor components are discussed as primary potential sources of differences in crystallization behavior. Calorimetric experiments capturing the crystallization and melting behavior of the industrial grade binary blends were compared to that of blends based on pure TAGs diluted in rapeseed oil, namely the combinations PPP-POP, SSS-SOS, PPP-SOS, and SSS-POP.