Among 118 AA-BAs detected from mouse and human feces, 90 AA-BAs were positively identified, of which 28 were confirmed based on pure standards (level 1, Table , highlighted in red), and 62 were identified based on predicted retention time (level 2, Table , highlighted in orange). For the remaining 28 AA-BAs, their amino acid conjugations could be determined, but the fine structures could not be identified due to the lack of reference standards (level 1, Table , highlighted in yellow).