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A mixture of flavonoid components was isolated from the fruit peel of three varieties of citrus native to Republic of Korea, Citrus leiocarpa Hort. ex Tanaka (CLHT), Citrus aurantium L. (CAL) and Citrus erythrosa Hort. (CEH), via 70% methanol extraction followed by ethyl acetate elution over a silica gel cartridge. The flavonoid components of the mixture were analyzed via high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) in positive-ion mode and a comparison of the reported data. Among 17 characterized components, two flavanones, four flavones and two coumarin derivatives in the fruit peel of the three varieties were identified for the first time. The individual characterized components were quantified via HPLC-UV. The flavanones dominated in CAL, whereas the flavones prevailed in CLHT and CEH. The antioxidant activity of the flavonoid mixture of the fruit peel was determined via DPPH•, ABTS•⁺ and reducing power assays. The antioxidant activity of CEH and CAL was greater than that of CLHT.

As watermelon is farmed primarily by protected and successive cultivation techniques, a number of pesticides are required for the control of pests and diseases. To evaluate the harmful effects of pesticides in watermelon and to guarantee consumers' safety, a rapid screening process for pesticides is required. A LC-MS/MS method was applied for the direct quantitation of 44 pesticide residues in watermelon. A Zorbax XDB-C(18) column was selected for analysis, with a mobile phase consisting of a gradient system of water and 5 mM methanolic ammonium formate. MS/MS experiments were performed in ESI positive ion and multiple reaction monitoring modes. The LOQs were in the range of 1-26 microg/kg, thereby indicating good sensitivity. Most of the recoveries ranged between 70-131% with RSDs < or = 20%. We suggested that the amount of pesticide residues such as pyroquilon (pyn), boscalid (bd), and dimethomorph (di) in amides (AM) and cinosulfuron (ci) in ureas (UR) may have been overestimated for the pesticides owing to increased alpha-error risk, whereas the amounts of pesticide residues, such as imibenconazole (ie) in the triazoles (TR) and fenpyroximate (fee) in the imidazoles (IM), may have been underestimated as the result of increased beta-error risk. The current method allowed for the rapid quantitation and identification of low pesticide levels in the watermelon samples. No pesticide residues were detected in any of the surveyed watermelons obtained from eight local markets in the Republic of Korea. Statistical analysis of the recoveries classified the 44 pesticides into nine groups and three overall categories.

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