Carbon xvii fatty acid methyl ester standard

Green coffee was provided by the Yunnan International Coffee Trading Center, made by wet processing technology, and originated from the variety of Catimor, which belongs to the Arabica coffee family. Triglyceride deuterium TAG 48:1 (15:0/18:1(D7)/15:0) and carbon XVII fatty acid methyl ester standard (internal standard) were purchased from Avanti Polar Lipids, pure chromatographic methanol, ammonia, chloroform, and hexane were purchased from Fisher, and chromatographic pure 10% ammonia was purchased from Shanghai Ampoule Experimental Technology Co. Ltd. (Shanghai, China). Chromatographic purity: dichloromethane for chromatographic purity was purchased from Sinopharm Chemical Reagent Co (Shanghai, China).

The fatty acid composition of pitaya seed oil was determined by the external standard method (Carbon XVII fatty acid methyl ester standard, Avanti Polar Lipids, U.S. Alabama) of potassium hydroxide methylation. Weigh 6–10 mg of pitaya seed oil accurately and 50 μL of 5 mg/mL of the internal standard carbon XVII fatty acid methyl ester, add 2 mL of 0.4 mol/L KOH methanol solution, vortex, and shake for 15 min, add 1 mL of n-hexane and 2 mL of 0.9% NaCl aqueous solution, shake for 2–3 s, centrifuge at 4500 rpm at 4 °C for 10 min, take the supernatant and transfer it to a 2 mL injection vial.
Gas chromatography-mass spectrometry (GC–MS) was equipped with a hydrogen flame ionization detector and DB-FastFAME column (30 m × 0.25 mm × 0.25 µm, 7890A gas chromatograph tandem hydrogen flame ionization detector, Agilent, Palo Alto, CA, U.S.). The measurement conditions were as follows: nitrogen as the carrier gas, injection volume of 1.0 μL, the inlet temperature of 260 °C, splitting ratio of 20:1; programmed temperature rise, and column initial temperature of 150 °C. The column was ramped up to 210 °C at 10 °C/min and held for 8 min, then ramped up to 230 °C at 20 °C/min and maintained for 6 min, and the detector temperature was 280 °C.