Simultaneous Separation and Determination of Chiral Amino Acids and Histamine in Doenjang by LC–MS/MS Based on a Novel Chiral Derivatization Probe Labeling

Doenjang is the most used fermented soy product in Asian countries. At present, the simultaneous determination of DL-amino acids and histamine in doenjang has not been reported. Therefore, an UHPLC–MS/MS method was developed based on a novel chiral derivatization probe DBD-M-Pro, enabling for the first time the simultaneous quantification of 10 DL-amino acids and histamine in doenjang samples from different regions. Achieving resolution (Rs) values of 1.62–6.31 for the 10 DL-amino acids. The limits of detection (LODs) for DL-amino acids and histamine ranged from 0.54 to 15.62 pmol. The intraday and interday precision (RSD) were 0.21%–10.63%, and the average recoveries were 93.18%–109.07%. This method was applied to analyze 12 doenjang samples from Northeastern China, Korea, and Japan. The results showed that there was a significant geographical distribution of DL-amino acids and histamine. Yanbian Korean doenjang from China showed a unique advantage in that the total amount of DL-amino acids was significantly higher than that from other regions, with histamine concentration generally increasing with longer fermentation times. This study provides a stable and reliable method for the simultaneous determination of chiral amino acids and histamine in fermented foods such as doenjang.