A metabolomics approach to identify and quantify the phytochemicals in watermelons by quantitative 1HNMR

•A simultaneous method developed to quantify L-citrulline and sugars Method is validated for linearity, precision, reproducibility, and stability.•Identity of the targeted compounds were further confirmed by HR-MS.•Eighteen metabolites were identified by 1H qNMR.•First report on qNMR method to quantify phytochemicals from watermelons.

Watermelon (Citrullus vulgaris) contains many health-promoting compounds, such as ascorbic acid, carotenoids, phenolic acids and amino acids including l-citrulline, arginine, and glutathione. Reported HPLC method for quantification of l-citrulline and sugars in watermelon involves, time-consuming sample preparation, post-column color development and detection with fluorescence and refractive index detectors. The present study describes development of a method to identify and quantify amino acids and sugars simultaneously from watermelon samples using quantitative proton NMR. Lyophilized watermelon samples (30–50 mg) were extracted with deuterium oxide (D2O) by sonication and the centrifuged extract was directly used for quantification and identification with 1HNMR. An external coaxial insert containing a 65 µL of 0.012% 3-(trimethylsilyl) propionic-(2,2,3,3-d4) acid sodium salt (TSP-d4) in D2O was used as a quantitative reference. The levels of l-citrulline and sugars were measured in less than 6 min. This rapid quantitation method was validated for specificity, linearity, accuracy, precision, reproducibility, and robustness. The limit of detection for l-citrulline was 38 µg/mL and the limit of quantification was 71 µg/mL; for sugars, the limits were 59–94 µg/mL and 120 µg/mL, respectively. This method can be used widely for confirmation and rapid quantitation of multiple compounds in large number of biological or breeding samples for routine analysis.

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