Phytochemical Constituents of Thai Dark Purple Glutinous Rice Bran Extract [Cultivar Luem Pua (Oryza sativa L.)]

Abstract

The isolation and identification of phytochemical constituents in the bran of dark-purple glutinous rice cultivar Luem Pua, was conducted. Luem Pua rice bran was extracted with hexane and methanol. The investigation of phytochemicals in the hexane extract was carried out after the fats were eliminated by saponification reaction. The isolation of the unsaponified fraction by reverse-phase high-performance liquid chromatography resulted in four sub-fractions, from which seven sterols and two triterpenoids were identified. The structures of all identified compounds were confirmed by gas chromatography-mass spectrometry and proton nuclear magnetic resonance spectroscopy. The chemical constituents in the methanol extract were also investigated using column chromatography and semi-preparative HPLC. The chemical composition of each fractions were analyzed by liquid chromatography coupled with tandem mass spectrometry via electrospray ionization mode (LC-MS/MS), together with comparison with literature data. This resulted in the identification of cyanidin-3-O-glucoside, a major anthocyanin contributing to the dark-purple color and the highly oxidative property of the rice, along with six phenolic compounds and eight flavonoids. The findings from this work helps support the potentials of Luem Pua rice for further applications in either health or pharmaceutical products.