Interplay of Polymorphic Transition and Mixed Crystal Formation in Model Fat Systems

Time-resolved small- and wide-angle X-ray scattering (SAXS/WAXS), differential scanning calorimetry (DSC), and small deformation oscillation were employed to investigate the crystallization kinetics of fat blends containing monoacid saturated triglycerides (H3) and a mixture of H3 and mixed acid saturated triglycerides (H2M, where H denotes long-chain saturated fatty acid and M denotes a medium-chain saturated fatty acid). For the H3 system, the time-resolved DSC signal revealed a two-step crystallization process aligned with the kinetic pathway identified via SAXS/WAXS. H3 first crystallizes in alpha form and quickly transitions into the beta polymorphic form. The rheological data on the complex modulus, due to the speed of the polymorphic transition, do not allow us to distinguish the two crystallization steps clearly. However, the alpha-beta transition complies well with literature data on monoacid saturated TAGs. The H3 + H2M system showed a two-step process in DSC and complex modulus, which could be associated with the polymorphic transition from the alpha to beta ' crystals. No further transition into the beta polymorph or segregation of the H3 fraction was detected, indicating the dominant role of H2M triglycerides. The SAXS data on the system suggest that H3 and H2M triglycerides formed a single solid phase, which is not supported by the DSC melting profile. The variation of cooling rate (5 vs 10 degree celsius/min) established minor differences in crystallization kinetics with their cause yet to be explored in greater detail. This study has generated valuable new insights concerning the polymorphic transition (alpha-beta ' and alpha-beta) in systems forming mixed crystals of monoacid and saturated mixed-acid TAGs using established methods and correlating them to blends of defined TAG group composition for the first time.