Structural identification of sour compounds in wine and tea by ambient ionization mass spectrometry according to characteristic product ion and neutral loss.

Sourness is an important food taste for human. A rapid, accurate method was used to generalize the structure similarity and diversity of sour compounds. Based on the product ion and neutral loss of sour compounds, ambient ionization techniques combined with quadrupole-Orbitrap mass spectrometry (AI-Q-Orbitrap) was employed. According to the behavior of sour compounds in the process of high collision dissociation (HCD) of MS/MS, three fragmentation pathway schemes were proposed: (1) charge-driven fragmentation and CO loss, (2) six-membered ring rearrangement and C-C cleavage, and (3) elimination rearrangement and HO, CO and CO loss in succession. Besides, structure information about characteristic product ions and characteristic neutral losses was summarized. Finally, multi-class sour compounds including monoacids, diacids, polyacids and phenolic acids in wine and tea were identified and compared. Therefore, sour compounds and their structure information can be determined by AI-MS based on characteristic product ion and neutral loss.