Chang-Hwan Oh

Rapid gas chromatographic screening of edible seeds, nuts and beans for non-protein and protein amino acids

Water extraction with subsequent picric acid treatment and solvent washing (ethyl acetate and diethyl ether) was employed for the rapid isolation of free amino acids from non-aqueous food samples. The isolated amino acids were subjected to N(O,S)-isobutyloxycarbonylation followed by solid-phase extraction and tert.-butyldimethylsilylation for direct analysis by gas chromatography and gas chromatography-mass spectrometry. When the present method was applied to nineteen food samples (common beans, seeds, and nuts), seventeen protein amino acids and fifteen non-protein amino acids were simultaneously screened. Eleven non-protein amino acids including gamma-aminobutyric acid, pipecolic acid, pyroglutamic acid, alpha-aminobutyric acid, alpha-aminoadipic acid, and beta-alanine were tentatively identified, and four compounds assumed to be non-protein amino acids remained unidentified.

Simultaneous gas chromatographic analysis of non-protein and protein amino acids as N(O,S)-isobutyloxycarbonyl tert.-butyldimethylsilyl derivatives

A unique derivatization procedure is described for the simultaneous determination of protein and non-protein amino acids present in aqueous samples. This procedure involves N(O,S)-isobutyloxycarbonylation combined with solid-phase extraction with subsequent tert.-butyldimethylsilylation for gas chromatographic analysis. Using this combined procedure, linear responses were obtained in the range of 10-100 ppm, with correlation coefficients varying from 0.991 to 0.999, for the free amino acids studied except for homocysteine (0.922) and homoserine (0.982). The relative standard deviations ranged from 0.7 to 5% for most amino acids with a few exceptions. Temperature-programmed retention index (I) sets as measured on DB-5 and DB-17 dual-capillary columns were characteristic of each amino acid and thus useful for the screening of amino acids by computer I matching. The mass spectral patterns of amino acid derivatives, exhibiting characteristic [M-57]+, [M-113]+, [M-131]+, [M-159]+, [M-174]+ and other ions, permitted rapid structural confirmation. The present method allowed simultaneous screening of free protein and non-protein amino acids when applied to seed samples such as almond, walnut, and sunflower seeds.

Capillary gas chromatography of protein amino acids as N(O,S)-isobutyloxycarbonyl tert.-butyldimethylsilyl derivatives in aqueous samples

A method for the quantitative determination of the nineteen protein amino acids by gas chromatography is described. The amino acids were allowed to react with isobutyl chloroformate in a basic aqueous medium and the resulting N(O,S)-isobutyloxycarbonyl (isoBOC) amino acids were extracted into an organic solvent after acidification. The isolated N(O,S)-isoBOC amino acids were then converted to stable tert.-butyldimethylsilyl (TBDMS) derivatives, which were analyzed by gas chromatography and gas chromatography—mass spectrometry. The characteristic [M - 57], [M - 113], [M - 159], [M - 174], etc. ions in the mass spectra of N(O,S)-isoBOC TBDMS derivatives enabled rapid confirmation of the amino acids. Temperature-programmed retention index (I) sets measured on DB-5 and DB-17 capillary columns were characteristic of each amino acid thus being useful for the quick identification by computer I matching. The overall extraction and derivatization yields of the amino acids studied were linear in the range of 20–80 ωg.

Flavonoids from Pueraria mirifica roots and quantitative analysis using HPLC

The flavonoids, wighteone (1), naringenin (2), genistein (3), isoliquiritigenin (4), daidzein (5), daidzin (6), genistein-8-C-β-d-apiofuranosyl-(1→6)-O-β-d-glucopyranoside (7), ambocin (8), and genistin (9) were isolated from roots of Pueraria mirifica. Chemical structures of the compounds were determined based on spectroscopic data analysis. Flavonoids 1, 2, 4, 7, and 8 were isolated for the first time. The contents of 6 flavonoids in P. mirifica roots was determined to be 2.5±0.01 (1), 14.8±0.09 (3), 18.6±0.18 (5), 17.3±0.11 (6), 10.4±0.05 (7), and 6.0±0.02 (9) mg/kg, respectively, using HPLC.

A new miroestrol glycoside from the roots of Pueraria mirifica

A new compound, miroestrol-3-O-β-D-glucopyranoside, was isolated from the roots of Pueraria mirifica (white kwao krua). The structure of the compound was established on the basis of NMR, ESI-MS, and IR spectroscopic data.