A study on the color deepening in red rice during storage.

To elucidate the mechanism of the color deepening phenomenon involving aged red rice samples, the time-dependent changes in the color and chemical composition of four different samples (freshly harvested, as well as those stored for 1, 2, and 5 years) were studied. A detailed study of the color change was carried out by obtaining the reflectance spectra of the samples. To investigate the underlying chemical changes, each sample was extracted with an appropriate solvent and analyzed by high-performance liquid chromatography, Folin-Ciocalteu assay, phloroglucinolysis, and mass spectrometry. A similar color change was induced via the photoirradiation of a fresh red rice sample. It is suggested that the chemical modifications of proanthocyanidins are responsible for the color change observed in red rice.