Terahertz spectroscopy for quantitatively elucidating the crystal transformation of chiral histidine enantiomers to racemic compounds

D-Histidine (D-His), L-Histidine (L-His), and their racemic compound DL-Histidine (DL-His) have different stereo chirality, making them intrinsic diverse functionalities to the living system. Identifying the configuration and crystal structures of enantiomers and the racemic compound is always the foremost requirement in processing protein foods. Although these features can be analyzed by spectroscopic technologies individually, it remains challenging to incorporate these complex methods into a facile analytical strategy. Herein, we propose a ter-ahertz spectroscopy with solid-state density functional theory to both distinguish the configurational difference and quantify the crystal transformation from L-His and D-His to DL-His. By comparison with X-ray diffraction analysis, the validity of the crystal transformation evaluation based on terahertz spectroscopy is verified. A normalized fitting line regarding the terahertz absorption frequency and intensity is calculated to quantitatively elucidate the crystal transformation from enantiomers to DL-His. Our findings provide a new analytical approach to the research on food chemistry.