  Triacylglycerols (TAGs) are among the most important ingredients in food,
cosmetic and pharmaceutical products. Many physical properties of such
products, incl. morphology, texture and rheology, are determined by the phase
behaviour of the included TAGs. Triglycerides are also of special interest for
the production of solid lipid nanoparticles, applied for controlled drug
delivery and for encapsulation of bioactive ingredients. In this paper, we
study the polymorphic behaviour of complex TAG mixtures, composed of 2 to 6
mixed TAGs, by differential scanning calorimetry and X-ray scattering
techniques, aiming to reveal the general rules for their phase behaviour upon
cooling and heating. The results show that two or more coexisting phases form
upon solidification $(\alpha$, $\beta'$ and/or $\beta)$, the number of which
depends strongly on the cooling rate and on the number of components in the
mixture. No completely miscible $\alpha$- or $\beta'$-phases were observed. The
structure of the most stable $\beta$ polymorphs, formed upon subsequent heating
of the solidified samples, does not depend on the thermal history of the
samples. For all mixtures studied, we observed one-component $\beta$ domains,
coexisting with binary mixed $\beta$ domains with composition and structure
which do not depend on the specific TAG ratio in the mixture. In other words,
for a mixture with $k$ saturated TAGs we observed $(2k-1)$ different $\beta$
phases. These conclusions provide some predictive power when analysing the
phase transition properties of TAG mixtures.
