Unravelling the hierarchical structure of saturated monoacid triglycerides during crystallization – a comprehensive time-resolved X-ray scattering study†

Abstract

Time-resolved studies are crucial for capturing the dynamic evolution of triglyceride structures during crystallization, providing insights into the self-assembly of diverse triglyceride structures across various length scales. While previous research has characterized triglyceride's polymorphisms and long spacings using wide-angle and small-angle X-ray techniques, time-resolved studies on the mesoscale of triglycerides have been limited, particularly in the study of crystalline nanoplatelets (CNPs) and their aggregates. This study pioneers the application of ultra-small-angle X-ray scattering (USAXS) for time-resolved analysis of commercial sources of saturated monoacid triglycerides. The methodology presented here integrates real-time synchrotron X-ray scattering (XRS) with differential scanning calorimetry (DSC), phase contrast microscopy (PCM), and cryo-scanning electron microscopy (Cryo-SEM) to investigate the crystallization behavior of a 30% dilution of palm stearin (PS) in high oleic sunflower oil (HOSO) and a 30% dilution of fully hydrogenated rapeseed oil (FHRO) in HOSO. Covering several orders of magnitude, this comprehensive multiscale approach enhances our kinetic understanding of triglyceride structural transformations. Both systems followed a polymorphic transition from α to β, with a transition from 2L(α) to 2L(β) lamellar stacking configuration. Our results suggest that structural evolutions in non-pure triglyceride systems advance gradually over extended timescales post-crystallization. While lamellae and CNP thicknesses decreased with the polymorphic transition, CNP size and aggregation changed in four distinct phases. We believe that the methodology presented here will greatly improve our understanding of the self-assembly of lipids, getting us closer to bottom-up optimization of triglyceride-based formulations in food.