Crystal growth of CO ₂ hydrate formed in the system of CO ₂ + water + trehalose toward the development of solid carbonated foods

Application of CO2 clathrate hydrate as a constituent of solid carbonated foods is an emerging new idea to utilize the large gas-storage capacity of this material. The CO2 gas concentration of CO2 hydrate is 50 times higher than the CO2 concentration in carbonated water. To design an industrial process for making CO2 clathrate hydrates and to determine the texture of hydrate foodstuffs, understanding the crystal growth dynamics and crystal morphology is essential. This study reports the visual observations of crystal growth of CO2 hydrate in the presence of trehalose under conditions relevant to potential food production. To classify the observation results, the subcooling temperature ΔTsub defined as the difference between equilibrium hydrate formation temperature, Teq and the experimental temperature, Tex was used as an index of the driving force for the crystal growth. The experiments were performed at the ∆Tsub range of 0.8 K to 4.9 K. At any ΔTsub, the formation and growth of the crystals were observed at the interface between the CO2 gas phase and the trehalose solution. The hydrate crystals covered the interface and grew into the liquid phase. The crystal morphology significantly depends on ΔTsub. The shape of crystals was polygonal at ΔTsub < 2.5 K, columnar at ΔTsub ≈ 3.5 K, and dendritic at ΔTsub > 3.8 K. The effects of CO2 hydrate crystal morphology in the system with trehalose, on the dynamics of hydrate slurry and the texture of hydrate food are discussed.