Deciphering the complex crystallization pathways of triglycerides in industrial fats

Solid fats play an important role in the food industry. In margarine, fat crystals stabilize the water-oil interface and form a three-dimensional network entrapping the continuous oil phase. The functionality of fat phases depends on both processing conditions and formulation, where high-melting triglycerides (TAGs) play a central role by contributing to the solid fat content. The growing demand for fats and oils and the equally so growing concern regarding palm oil facilitates the search for alternative structuring approaches. New compositions can be derived via various TAG modification routes, e.g., hydrogenation and interesterification. Replacing palm oil entirely requires entering a largely unexplored composition space while still maintaining functionality. Designing fat blends that perform similar to palm-oil-based systems demands a deep understanding of how TAG composition governs kinetic phase behavior, miscibility, and polymorphic crystallization. While phenomena such as mixed crystal formation, molecular compound formation, and phase separation have been well-studied in binary mixtures, translating these insights into complex industrial hardstocks remains challenging. Even subtle compositional shifts – such as substituting palmitic acid with stearic acid – can profoundly alter crystallization kinetics and overall product performance. The intricacy in the relation of TAG composition and crystallization pathways is explored in this thesis. The aim is to bridge the gap between industry applications and academic research. The role of the composition is deciphered by isolating three main agents: H3 (three long-chain saturated fatty acids), H2M (two long-chain saturated plus one medium-chain saturated), and H2U (two long-chain saturated plus one unsaturated). The considerable lack of knowledge on the melting group H2M including TAGs like PLaP and SSLa is addressed by exploring their polymorphic crystallization pathways and their contribution to the kinetics in mixed systems. Further, this work investigates the role of the dominant saturated TAG fatty acid (palmitic or stearic acid) in different TAG sources. Crystallization pathways were studied in both model binary/ternary TAG blends and industrial hardstocks (simplified to pseudo-binary/-ternary systems), with a focus on early-stage processes where polymorphic transitions and phase segregation effects overlap. Differential scanning calorimetry (DSC), rheology, and in situ small- and wide-angle X-ray scattering (SAXS/WAXS) were combined to capture kinetic and structural evolution. A complementary review article examined the structure of TAG crystals and mixtures with a focus on X-ray scattering techniques. It summarized established data analysis approaches and identified key limitations, particularly in studying early-stage crystallization in diluted systems and in translating structural information from pure components to complex mixtures. A pure component study on the H2M triglycerides PLaP/PPLa and SLaS/SSLa showed that molecular asymmetry and minor differences in chain length mismatches significantly alter stacking preferences and slow polymorphic transitions. The impact of H2M triglycerides on the crystallization pathways in blends revealed their ability to inhibit the phase transition of H3 triglycerides (alpha → beta). Furthermore, multiple co-existing beta’ phases differing in composition and dissolution temperatures could be determined hinting towards partial immiscibility. This trend further extended to (pseudo) ternary blends. H2U triglycerides also influence the phase transitions of H3 triglycerides through selective co-crystallization. This work compared systems differing in their predominant saturated fatty acid (palmitic versus stearic acid). The kinetic pathways differed greatly: palmitic-based systems showed mixed crystal formation and fast polymorphic transition, yet, phase segregation into a H3-rich could not be prevented. In contrast, the stearic acid-based system showed a prolonged stability of an H3-rich phase. Similar trends were observed in pseudo-ternary systems. A direct comparison of pure TAG blends and industrial hardstocks simplified to pseudo binary and ternary was made. This revealed the impact of molecular diversity and highlighted the difficulty of translating knowledge gained for pure components into application-relevant systems. From a methodological perspective, it was shown that a combination of DSC, in situ SAXS/WAXS, and rheology allowed extracting nuanced kinetic information. The intricate crystallization pathways are characterized by slow restructuring processes superimposed by the evolution of new phases and compositional changes in the existing phases. This clearly demonstrates that determining a “transition time” from any crystallization curve holds crucial information on polymorphic transitions, mixed crystal formation, and fractionation. Disentangling these phenomena is possible by informed measurement strategies, combination of techniques, and composition-sensitive data interpretation. This thesis provides new insights helping to bridge the gap between academia and industry regarding the effect of TAG composition on crystallization kinetics. Of special interest remains the translation from pure component behavior into mixtures. Addressing this challenge will require targeted studies on binary mixtures to resolve key interactions, alongside improved TAG compositional analysis to directly connect molecular makeup with functionality. This enables informed formulation strategies, moving beyond trial-and-error to predict composition-structure-performance relationships.