Abstract: This study established a novel method for measuring the contents of asparagine (Asn) and glutamine (Gln) in fruits and vegetables based on enzymatic hydrolysis combine with ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). After enzymatic hydrolysis with Pronase E, samples were treated with butylated hydroxyanisole as an antioxidant. The supernatant was collected for analysis by UPLC-MS/MS. The chromatographic separation was accomplished on a Phenomenex kinetex F5 column using gradient elution with a mobile phase consisting of methanol and 0.02% formic acid in water. The mass spectrometer was equipped with an electrospray ionization source and operated in the positive ion mode with multiple reaction monitoring (MRM), and quantification was achieved using stable isotope-labeled internal standards. The calibration curves for Asn and Gln showed a good linearity in the range of 10–1 000 ng/mL (R2 > 0.999), with limit of detection (LOD) and limit of quantification (LOQ) of 1.5 and 5.0 mg/100 g, respectively. The recovery rates were in the range of 80.0%–112.8% with relative standard deviations (RSDs) of 1.2%–9.1%. The contents of Asn and Gln in 49 common vegetables and 50 common fruits were determined by the UPLC-MS/MS method. In vegetables, the average total content of Asn and Gln decreased in the order of bean > potato > onion and garlic > edible fungi > melon > solanaceous > cabbage. Notably, the total contents of Asn and Gln in beans were significantly higher than those in green leafy vegetables (P < 0.01). In fruits, the average total content of Asn and Gln decreased in the order of drupes > melons > aggregate fruits > berries > citrus > banana > nuts, and drupes had significantly higher total contents of Asn and Gln than nuts (P < 0.05). These findings suggested that individuals with urea cycle disorders should eat more nut fruits and green leafy vegetables, with less asparagine and glutamine, in daily life, especially vegetables and fruits with higher ratio of branched-chain amino acids to Asn plus Gln such as Chinese cabbage, Auricularia auricula, green onion, coconut juice, longan, and pomelo, and should eat less vegetables and fruits with lower ratio of branched-chain amino acids to Asn plus Gln such as potato, pumpkin, green bean, cantaloupe, red plum and yellow peach.

Key words: asparagine; glutamine; vegetables; fruits; urea cycle disorder; daily diet