Chiral analysis of derivatized amino acids from kefir by gas chromatography

Abstract

The amino acids present in the kefir samples were derivatized using different alkyl chloroformates combined with alcohols and chromatographed on a (3-O-butanoyl-2,6-di-O-pentyl)-γ-cyclodextrin (Lipodex E) chiral gas-liquid chromatographic column. The combination of derivatization reagents that led to better chromato- graphic performance for standard amino acid solutions was critically compared. All the chloroformate/alchohol mixtures lead to fast and quantitative reactions. However, the ethyl chloroformate/ethanolmixturewas selected since the number of enantioseparated amino acid derivativeswas higher. The derivatizationwas applied to samples of kefir grains grown in raw and in skimmed UHT milk. The samples were previously pretreated by elution froma low-pressure ion-exchange columns. Standard addition calibration curves have been used for the quantitative determinations of amino acid derivatives in both samples, and the figs. of merit of the proposed method have been assessed. The L-and D-configuration of D-and L-alanine, D-and L-valine,D-proline, L-threonine, aspartic and glutamic acids, methionine, and cysteine were detected and quantitatively determined.