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

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 (HNMR)-H-1. An external coaxial insert containing a 65 mu L of 0.012% 3-(trimethylsilyl) propionic-(2,2,3,3-d(4)) acid sodium salt (TSP-d(4)) 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 mu g/mL and the limit of quantification was 71 mu g/mL; for sugars, the limits were 59-94 mu g/mL and 120 mu g/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. (C) 2016 Elsevier B.V. All rights reserved.