Chiral MEKC-LIF of amino acids in foods: Analysis of vinegars

Abstract

The formation of D-amino acids (D-aa) in many fermented foods depends, among other factors, on the particular fermentation conditions, the action and autolysis of the microorganisms involved. In this sense, the analysis of chiral amino acids is an interesting analytical strategy for food scientists, since these compounds can be used as bacterial markers and can help e.g., to detect adulterations, microbiological contaminations, etc. In this work, a fast and sensitive method based on micellar electrokinetic chromatography with laser induced fluorescence (MEKC-LIF) has been developed to analyze and quantitate L- and D-aa in vinegars. The chiral-MEKC-LIF procedure uses 100 mM sodium tetraborate, 30 mM SDS and 20 mM -CD at pH 9.7 as running buffer, obtaining a good separation of the main vinegar L/D amino acids previously derivatized with fluorescein isothiocianate. Namely, L/D proline, alanine, arginine, glutamic and aspartic acid, plus the non chiral amino acid -aminobutyric acid are separated in less than 20 min with high efficiency (up to 720,000 plates/m) and good sensitivity (LODs lower than 16.6 nM were achieved). Several D-aa were detected and quantified in balsamic, sherry, white wine, and cider vinegars using this MEKC-LIF procedure, observing interesting differences in their L- and D-aa profiles and contents.