Identification and Determination of Rubrofusarin, Rubrofusarin Isomer, and Their Quinone Forms in Grains Using High-Resolution Mass Spectrometry

Fungi of the genus Fusarium can produce secondary metabolites such as naphthopyrones and naphthoquinones that are toxic and expected to threaten the food and feed safety. In this study, the occurrence of rubrofusarin, rubrofusarin isomer, and their quinone forms in grains was identified and confirmed using ultrahigh-performance liquid chromatography coupled with hybrid quadrupole orbital ion trap mass spectrometry (Q-Orbitrap MS). The quantitation of these compounds in grain samples was also investigated using Q-Orbitrap MS. The results showed the concentrations of rubrofusarin ranged from 3.278 to 33.82 μg/kg, from 0.815 to 61.86 μg/kg, and from 7.362 to 47.24 μg/kg for the maize, rice, and wheat samples, respectively. By comparison, the abundances of their quinone forms were relatively lower, and the concentration of quinone form of rubrofusarin isomer was relatively higher than that of quinone form of rubrofusarin. These compounds were also confirmed to coexist with other known Fusarium mycotoxins. The data-dependent tandem mass spectra obtained from the Q-Orbitrap MS were validated to provide a wealth of valuable information that allowed for advanced data interpretation for solid confirmation of these compounds in grains. To the best of our knowledge, this is the first study that concerns the occurrence and quantitation of rubrofusarin, rubrofusarin isomer, and their quinone forms in grains.