Terahertz spectroscopy detection of L-lysine hydrate dehydration process

L-lysine (Lys), an essential amino acid for humans and mammals, must be obtained from food. It is highly soluble in water and can form L-lysine hydrate (Lys·H₂O) under certain conditions, negatively affecting food quality. As temperature increases, Lys·H₂O can dehydrate to become Lys. This study employs terahertz time-domain spectroscopy, infrared spectroscopy, and X-ray diffraction to characterize Lys and Lys·H₂O, analyzing the detection capabilities of different spectral methods. In addition, Density Functional Theory (DFT) simulations were used to verify the experimental results. Thermogravimetric analysis (TG) was employed to study the dehydration process of Lys·H₂O with increasing temperature. The experimental results indicate that the dehydration process involves the removal of both free water and crystal water, completing at approximately 100 °C. Terahertz time-domain spectroscopy provides detailed characterization of this process. The relationship between characteristic peak absorption intensity and temperature during dehydration is successfully analyzed through Boltzmann fitting and first-order derivative analysis. This study effectively monitors the transition of Lys·H₂O to anhydrate, offering a novel method for the quantitative analysis of the hydrate dehydration process.