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Fumonisins are mycotoxins mainly produced by Fusarium verticillioides, which is a major contaminant of corn. However, there are sporadic reports of fumonisin contamination in wheat worldwide. The rice adherent fungus Gibberella fujikuroi is taxonomically closely related to F. verticillioides. Therefore, the potential risk of fumonisin contamination in rice and wheat is significant. Previously, a sensitive detection method utilizing liquid chromatography with tandem electrospray mass spectrometry (LC-ESI-MS-MS) was developed for the determination of fumonisins in brown rice. In the present study, the incidence of fumonisins in brown rice and wheat harvested in Japan was investigated using LC-ESI-MS-MS. Forty-eight rice samples and 47 wheat samples were screened and analyzed for the major B-type fumonisins: fumonisin B1 (FB1) and fumonisin B2 (FB2). About 1 kg of rice or wheat seed was divided into three subsamples, and 10 g from each subsample was used for the analysis. The limits of detection were 0.012 and 0.011 mg/kg for FBt and FB2, respectively, in rice samples and 0.010 and 0.008 mg/kg for FB1 and FB2, respectively, in wheat samples. The mean (standard deviation) recoveries of FB1 spiked at 0.50 mg/kg into toxin-free rice and wheat samples were 77.6 (4.2)% and 84.5 (3.1)%, respectively. One of the wheat samples was positive for FBt with a value greater than the limit of detection,but no fumonisin was found in any of the rice samples. This is the first report of fumonisins detected in Japanese wheat.

Mycotoxin contamination in rice is less reported, compared to that in wheat or maize, however, some Fusarium fungi occasionally infect rice in the paddy field. Fumonisins are mycotoxins mainly produced by Fusarium verticillioides, which often ruins maize. Rice adherent fungus Gibberella fujikuroi is taxonomically near to F. verticillioides, and there are sporadic reports of fumonisin contamination in rice from Asia, Europe and the United States. Therefore, there exists the potential risk of fumonisin contamination in rice as well as the need for the validated analytical method for fumonisins in rice. Although both natural and spiked reference materials are available for some Fusarium mycotoxins in matrices of wheat and maize, there are no reference materials for Fusarium mycotoxins in rice. In this study, we have developed a method for the preparation of a reference material containing fumonisins in Thai rice. A ShakeMaster grinding machine was used for the preparation of a mixed material of blank Thai rice and F. verticillioides-infected Thai rice. The homogeneity of the mixed material was confirmed by one-way analysis of variance, which led this material to serve as an in-house reference material. Using this reference material, several procedures to extract fumonisins from Thai rice were compared. Accordingly, we proved the applicability of an effective extraction procedure for the determination of fumonisins in Japanese rice.

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