*2.3. LC-MS/MS Analysis*

The PAs in the samples were measured using a LC-MS/MS system consisting of an UHPLC (Ultimate 3000, Thermo Scientific, San Jose, CA, USA) and a Triple Stage Quadrupole mass spectrometer (TSQ Vantage, Thermo Scientific, San Jose, CA, USA), as described previously with minor modifications [21]. Briefly, chromatographic separation was achieved on 150 × 2.1 mm, 1.9 μm particle sizes, C18 Hypersil Gold column fitted with a guard column (Thermo Scientific, Dreieich, Germany). Eluent A was 100% water with 0.1% formic acid and 5 mM of ammonium formate. Eluent B was 95% methanol and 5% water with 0.1% formic acid and 5 mM of ammonium formate. A stepwise gradient elution was conducted as follows: 0–0.5 min for 95% A/5% B, 7.0 min for 50% A/50% B, 7.5 min for 20% A/80% B, 7.6–9.0 min for 100% B and 9.1–15 min for 95% A/ 5% B. A flow rate of 300 μL/minute was applied and 10 μL of each sample was injected. The column temperature was maintained at 40 ◦C. Details of the mass parameters are listed in supporting data S1, Table S1.
