Phenyl β d glucopyranoside

Metabolite extraction and quenching were performed on plate with 1.5 mL ice cold extraction medium (90% methanol, 10% water) containing 1 µg/mL ribitol (A5502, Sigma Aldrich), phenyl β-d-glucopyranoside (292710, Sigma Aldrich), isoguanosine (sc-207768, Santa Cruz, Dallas, TX, USA), d4-succinate (293075, Sigma Aldrich) and methyl-tyrosine (M8131, Sigma Aldrich) as the internal standard. Cells were detached on ice by using a cell scraper, transferred into screw-cap tubes prefilled with 300 mg glass beads (G4649, Sigma Aldrich) and immediately frozen in liquid nitrogen until homogenization. Cells were homogenized using a Precellys tissue homogenizer (P000669-PR240-A, Bertin instruments, Montigny-le-Bretonneux, France) at −10 °C. Three cycles of homogenization for 15 s at 6500 rpm were applied with 10-s breaks in between cycles. Samples were then centrifuged (20,000× g) for 10 min at 4 °C to remove cell debris and protein precipitates, and 500 µL of each supernatant was transferred into two new reaction tubes for GC-MS and LC-MS analyses. Finally, extracts were dried using a vacuum rotator (Eppendorf, Hamburg, Germany) and flushed with nitrogen. The DNA content in the extracts was measured using NanoDrop 1000 (Thermo Fisher Scientific).

Standards (glucose, galactose, fructose, sucrose, lactose, and maltose), hexamethyldisilazane (HMDS), trifluoro acetic acid (TFA), pyridine, and hydroxylamine hydrochloride were purchased from Sigma-Aldrich Co. (St. Louis, MO, USA). Other reagent-grade chemicals and HPLC-grade solvents (ethanol, methanol, and water) were obtained from Thermo Fisher Scientific (Waltham, MA, USA).
The sugar standard solution was prepared by weighing 50 mg of each of the standards in a 50 mL volumetric flask and dissolving it in 50% methanol. The solutions were stored in a refrigerator at 4 °C until further use in the experiments. Phenyl β-d-glucopyranoside (Sigma-Aldrich) was used as an internal standard.

All chemical solvents and reagents for extraction and gas chromatography (GC) derivatization were high-performance liquid chromatography (HPLC) and analytical grade and were purchased from RCI Labscan Ltd. (Pathumwan, Bangkok, Thailand) and Sigma-Aldrich (St. Louis, MO, USA), respectively. All internal standards, including tetracosane (IS I), 5α-cholestane-3β-ol (IS II), phenyl-β-d-glucopyranoside (IS III), ρ-chloro-l-phenylalanine (IS IV), and dodecanoic acid ethyl ester, were standard grade and were purchased from Sigma-Aldrich. In addition, all reference standards for metabolomics and flavoromics, a C6–C30 n-alkane mixture used to measure linear retention indices, and 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2-azobis(3-ethylbenzothialzoline-6-sulfonic acid) (ABTS), and Folin–Ciocalteu reagent were purchased from Sigma-Aldrich.