Structural Behaviour of Lipid Droplets in Protein-stabilized Nano-emulsions and Stability of α-Tocopherol

A stearin-rich milk fraction was used, alone or in combination with α-tocopherol, for the preparation of oil-in-water sodium caseinate-stabilized nano-emulsions. Fat droplets in these two emulsions were characterized for their size distribution and physical stability against aggregation–coalescence, for their heat-induced structural behaviour, and for their ability to protect α-tocopherol during oxidation. Inclusion of α-tocopherol led to changes in the particle size distributions of fat droplets: in the presence of α-tocopherol, approximately 75% of fat droplets were lower than 1 μm, instead of 100% in the absence of α-tocopherol. On the other hand, thermal transitions observed by differential scanning calorimetry showed that supercooling (the increase in differences between temperature of initial crystallization and melting completion) was higher in the emulsified milk fat samples containing α-tocopherol. In addition to a decrease in the temperature of fat crystallization leading this change in the supercooling effect of α-tocopherol, small- and wide-angle X-ray diffraction patterns (SAXS and WAXS, respectively) observed under cooling and re-heating cycles showed that heat-induced polymorphic transitions from\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{2L}}_{\text{ $ \alpha $ }} \to {\text{2L}}_{{\text{ $ \beta $ }}\prime } $$\end{document} forms were more impeded in the emulsion containing α-tocopherol. Immobilisation of α-tocopherol in fat droplets composed by high melting temperature milk fat triglycerides seemed to lead to its protection against degradation.