Investigation of storage time-dependent alterations of enantioselective amino acid profiles in kimchi using liquid chromatography-time of flight mass spectrometry

Although naturally abundant amino acids are represented mainly by l-enantiomers, fermented foods are known to contain various d-amino acids. Enantiospecific profiles of food products can vary due to fermentation by bacteria, and such alterations may contribute to changes in food properties that would not be dependent exclusively on l-amino acids. Therefore, more attention should be paid to the study of temporal alterations of d-amino acid profiles during fermentation process. However, there have been very few studies reporting time-dependent profiling of d-amino acids because enantioseparation of widely targeted d-amino acids is technically difficult. This study aimed to achieve high throughput profiling of amino acids enantiomers. Enantioselective profiling of amino acids using CROWNPAK CR-I(+) column, liquid chromatography, time of flight mass spectrometry, and principle component analysis was performed to investigate time-dependent alterations in concentrations of free d- and l-amino acids in kimchi stored at 4°C or 25°C. We demonstrated significant changes in d- and l-amino acid profiles in kimchi stored at 25°C. In particular, concentrations of the amino acids d-Ala, d-Ser, d-allo-Ile, d-Leu, d-Asp, d-Glu, and d-Met became higher in kimchi with storage time. This is the first report of time-dependent alterations of d- and l-amino acid contents in kimchi. This study showed that our analytical method of enantioselective detection of amino acids using liquid chromatography time-of-flight mass spectrometry (LC-TOFMS) with CROWNPAK CR-I(+) enables high throughput food screening and can be recommended for advanced studies of the relationship between d-amino acid content and food properties.