Co‐crystals of Beeswax and Various Vegetable Waxes with Sterols Studied by X‐ray Diffraction and Differential Scanning Calorimetry

In this study, mixtures of purified wax and sterols were melted and subsequently cooled. Using X‐ray diffraction of the mixed, solid phase, it was shown that for up to 30–40 wt% sterols no measurable re‐crystallisation of sterols occurred, i.e. the sterols became dissolved at a molecular level. Probably a form of amorphous co‐crystals of sterols and wax is formed if the molecular ratio does not exceed 1:1. Differential scanning calorimetry (DSC) suggests that a minor amount of pure sterols could already be present at lower sterol levels. This may be because of the higher temperature at which the microstructure is probed when using DSC—melting of the wax might lead to crystallisation of the sterols. For application in foods, the structure as probed by X‐rays at ambient temperatures is more relevant. When sunflower wax and rice bran wax are used, prevention of sterol crystallisation is even more pronounced, probably because the melting temperatures of these waxes are closer to the melting temperature of sterol crystals. Replacing the beeswax with a saturated fat (heRP70), sunflower oil, or jojoba wax (a liquid wax) substantially increases the amount of crystalline sterols. The difference between the various waxes and fats was qualitatively the same for X‐ray diffraction and DSC. Stanols can be incorporated in the same manner and up to similar concentrations. Another insoluble nutritional compound, ursolic acid, has a greater tendency to crystallise in wax. This is probably because the melting temperature of ursolic acid is much higher than that of wax.