Preparation of core–shell CaCO3 capsules via Pickering emulsion templates

Micron size and food grade pristine CaCO3 particles were used to stabilize an oil in water Pickering emulsion. The particles also acted as nucleation sites for the subsequent crystallization of CaCO3 with the addition of CaCl2 and CO2 gas as precursors. After the controllable crystallization process, a dense CaCO3 shell with a few microns in thickness was formed. The CaCO3 shell was proven to be calcite without the presence of crystallization modifiers. The crystallization speed and the shell integrity were controlled by manipulating the addition of CaCl2 amount during the different crystallization stages; therefore, the homogeneous nucleation in the bulk was almost inhibited, and the heterogeneous nucleation at the oil–water interface on pristine CaCO3 particles was the main contribution to the growth of the shell. The encapsulated limonene flavor in CaCO3 capsules showed a prolonged release in neutral water at 85 °C, while a burst release at pH 2 water as expected. The method is a simple and scalable process for creating inorganic core–shell capsules and can be used for producing food grade capsules for controlling the flavor release or masking undesirable taste in mouth.

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► Large scale preparation of high quality CaCO3 core/shell capsules was achieved.
► CaCO3 particles were used as Pickering emulsion stabiliser and the nucleation sites.
► Homogeneous nucleation in the bulk was inhibited by control the addition of CaCl2.
► Without any additives, highly pure CaCO3 capsules showed prolonged flavor release.