Quinic acid

The organic acid profile of the coffee samples was determined by high-performance liquid chromatography using the method published by Luu et al. (2023) [17 (link)]. Briefly, the brewed coffee samples were filtered through a 0.22 µm nylon syringe filter. The filtrate (10 µL) was injected into a 5 µm Thermo Scientific HyperSil Gold aQ column (250 × 4.6 mm) (Thermo Fisher Scientific, Bremen, Germany) attached to a Waters Alliance HPL e2695 with a diode array detector (Waters Corporation, Milford, MA, USA). An isocratic solvent system comprising 50 mM phosphate buffer at pH 8.2 with a flow rate of 0.70 mL/min was set up. The total run time was 20 min, while the separation of organic acids was visualized at 214 nm (UV detection). The standards for organic acids used were HPLC-grade. Acetic acid was purchased from Merck (Darmstadt, Germany). Oxalic acid, malic acid, citric acid, succinic acid, and tartaric acid were purchased from Megazyme (Wicklow, Ireland). While formic acid, ascorbic acid, and propionic acid were bought from Sigma Aldrich (St. Louis, MO, USA). Fumaric acid and quinic acid were bought from Tokyo Chemical Industry (Portland, OR, USA). The HPLC chromatograms of the standards and samples are shown in Supplementary Figure S1.