Quantification of ergothioneine in Aspergillus oryzae-fermented rice bran by a newly-developed LC/ESI-MS/MS method

The ingestion of l-ergothioneine (EGT) is thought to provide health benefits. It is also expected that the fermented rice bran or rice with Aspergillus oryzae (A. oryzae) would be EGT-rich and easily available foodstuffs. Based on this concept, a liquid chromatography/electrospray ionization-tandem mass spectrometry (LC/ESI-MS/MS) method was developed to identify and quantify EGT in the A. oryzae-fermented rice bran and rice. We optimized the derivatization protocol using 2-iodo-N-(8′-quinolinyl)acetamide, which improved the LC retention and ESI-MS/MS sensitivity of EGT. The pretreatment procedure and LC/ESI-MS/MS conditions were also optimized to achieve the sensitive (limit of quantification, 0.080 μg/g), precise (intra- and inter-assay relative standard deviations, ≤ 7.8% and 5.8%, respectively) and accurate (94.9–100.0%) quantification of EGT in the samples. The EGT contents in the fermented rice bran were 176 ± 39 μg/g (mean ± standard deviation, n = 3), which were greater than those in the fermented white rice (59.8 ± 20.4 μg/g) and brown rice (85.5 ± 32.3 μg/g). The EGT in rice bran was enriched 140 times by the fermentation for 45 h. These results revealed that rice bran is a suitable material for making the EGT-rich foodstuffs by the A. oryzae-fermentation.