Fig. 3

Identification of tryptophol acetate secreted by Kluyveromyces marxianus. a HPLC chromatogram of (i) tryptophol acetate extracted from the K. marxianus monoculture crude with a retention time of 13.84 min (peak indicated in red); tryptophol acetate molecular structure is indicated. (ii) Tryptophol acetate identified in the kefir crude extract (peak shown in red at the same retention time). b MS spectrum acquired in positive enhanced mass spectrometry for the identified tryptophol acetate peak in the kefir crude extract (between 13.72 and 14.05 min). c Calibration curve of tryptopol acetate in the kefir crude extract constructed with the synthetic compound. The broken lines indicate the concentration of tryptophol acetate in the kefir extract (210 μM)