Quantification of Proline-containing Cyclic Dipeptides by LC-MS/MS

The cyclic dipeptides, 2,5-diketopiperazines (DKPs), draw attention as bioactive and taste compounds. DKPs, especially those containing Proline (Pro), are contained in heated and fermented foods. Herein, we developed a method for a simultaneous quantitative analysis of Pro-containing DKPs using LC-MS/MS. After optimizing the LC-MS/MS conditions, the developed method was applied to quantify Pro-containing DKPs in Goishi tea, which is a post-fermented tea produced by a two-step aerobic-anaerobic fermentation process. Consequently, 17 kinds of Pro-containing DKPs could be quantified, and the total amount of Pro-containing DKPs was 3.40 mg/L. The recovery in a spiked test was 93 - 117%, which is satisfactory. We believe that the developed method can be used to elucidate the role of Pro-containing DKPs in food.