Structures of some bioactive phytochemicals in bran extract of the black rice cv. Riceberry that had demonstrated anti-cancer activity in leukemic cell line were investigated. After saponification with potassium hydroxide, separation of the unsaponified fraction by reversed-phase high performance liquid chromatography (HPLC) resulted in four sub-fractions that had a certain degree of anti-proliferation against a mouse leukemic cell line (WEHI-3 cell), this being IC50 at 24 h ranging between 2.80–467.11 μg/mL. Further purification of the bioactive substances contained in these four sub-fractions was performed by normal-phase HPLC. Structural characterization by gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance spectroscopy (NMR) resulted in, overall, the structures of seven phytosterols and four triterpenoids. Four phytosterols, 24-methylene-ergosta-5-en-3β-ol, 24-methylene-ergosta-7-en-3β-ol, fucosterol, and gramisterol, along with three triterpenoids, cycloeucalenol, lupenone, and lupeol, were found in the two sub-fractions that showed strong anti-leukemic cell proliferation (IC50 = 2.80 and 32.89 μg/mL). The other sterols and triterpenoids were campesterol, stigmasterol, β-sitosterol and 24-methylenecycloartanol. Together with the data from in vitro biological analysis, we suggest that gramisterol is a significant anti-cancer lead compound in Riceberry bran extract.
Volatile components of uncooked Khao Dawk Mali 105 brown rice were extracted using indirect steam distillation under reduced pressure and controlled temperature in order to prevent cooking. Analysis of the fresh extract by capillary gas chromatography-mass spectrometry revealed that there were >140 volatile constituents. Among these, 70 volatiles were identified, including 2-acetyl-1-pyrroline (2AP), a key aroma compound of cooked rice. Further study concentrated on an improved method for the quantification of 2AP in uncooked brown rice. The method was simplified by utilizing a solvent extraction procedure. Quantitative analysis was performed using a capillary gas chromatographic system employing a flame ionization detector with the aid of a more selective column, CP-Wax 51, for amines. This improved chromatographic system had remarkable detection sensitivity for 2AP in the rice extracts so that 2AP in an extract of only 0.5 g of uncooked Khao Dawk Mali 105 brown rice could be detected.
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