Terahertz time-domain spectroscopy for monitoring the dynamic process of tryptophan photooxidation and the concentration determination

Tryptophan, as an essential amino acid, can only be obtained through diet, and its production and processing are accompanied by different degrees of oxidation leading to poor absorption. Therefore, it is important to pay attention to the degree of oxidation of tryptophan promptly. Conventional tests can assess tryptophan oxidation levels by monitoring the amount of tryptophan, but most require complex pre-processing and time-consuming testing procedures. Based on this, we propose a rapid method to estimate the degree of tryptophan oxidation using terahertz spectroscopy. We confirmed the relationship between the terahertz characteristic absorption peaks of tryptophan and its content combined with X-ray diffraction and infrared spectroscopy. It was further found that the tryptophan content could be effectively determined based on the characteristic peak area. The findings of this study offer a novel and practical technique for quickly determining the level of tryptophan oxidation in food or dietary supplements.