Influence of Monounsaturated Triglycerides on the Crystallization Pathway of Fully Saturated Triglycerides

Abstract

The effect of composition on the polymorphic crystallization in blends of fully saturated and monounsaturated triglycerides was investigated (H3 denotes fully saturated, and H2U denotes monounsaturated triglycerides). Fully hydrogenated rapeseed oil (FHRO) and palm oil stearin (POSt) were used as H3 sources. Palm oil (PO) served as an H2U source. Different H3/H2U ratios and cooling rates (1, 5, and 10 °C min^–1) were investigated. Differential scanning calorimetry, time-resolved small- and wide-angle X-ray scattering, and oscillatory shear experiments were employed to investigate the melting behavior as well as the nano- and microstructural development. The data reveal different kinetic pathways, even selective cocrystallization, depending on the molecular makeup of the H3 fraction. The POSt-PO blends first crystallize in an α phase that transitions into coexisting β′ and β phases. The FHRO-PO blends showed a longer persisting α phase that transitions into β even before a β′ phase could be identified. This indicated separate crystallization of H3 triglycerides. The polymorphic pathways are compared to the melting behavior and microstructural development during crystallization. Further, the question of mixed crystal formation in the H3 fraction of the FHRO-PO blends was addressed by studying H3 blend replicates in the absence of H2U triglycerides. This paper is the second part of a series investigating the interplay of polymorphic transition and mixed crystal formation.

A study on the isothermal crystallization pathways of trisaturated triglycerides of stearic (S) and palmitic (P) origin in the presence of monounsaturated triglycerides reveals multiple coexisting crystalline phases and phase segregation in S-containing triglycerides. The polymorphic pathway is further characterized by a slow lamellar restructuring.