A sealed heated mixture of maltol (Mal) and porous calcium silicate (Florite® RE:FR) was prepared by heating the physical mixture in a sealed container. The amorphization of the Mal crystals in the sealed heated mixture (FR:Mal = 9:1 or 7:3) was observed by X-ray diffraction and differential scanning calorimetric measurements. At the same time, a marked discoloration was also observed in the sealed heated mixture, which showed a color change from initially white to yellow or light brown. On the basis of Fourier transform infrared spectroscopy, the discoloration seems to be due to the ionization of Mal molecules on the FR surface. The discoloration of the mixture during heating was accelerated by increasing the heating temperature and the heating time. The addition of colloidal silicon dioxide (Reolosil® QS-102:REO) affected the discoloration. It was found that an increase in an amount of REO added inhibited the discoloration during sealed heating.
Hanawa, T., Ikoma, R., & Sugihara, M. (1997). Preparation and characterization of sealed heated mixture of sublimable compound and porous calcium silicate II: Investigation of the interaction between maltol and porous calcium silicate surface. International Journal of Pharmaceutics, 154(1), 1–8. https://doi.org/10.1016/S0378-5173(97)00124-5