Analytical evaluation of fatty acid esters of hydroxy fatty acid quantity in fermented brown rice and rice bran (FRBA)

•Fermented brown rice and rice bran with Aspergillus oryzae (FBRA) contained FAHFAs.•Rice bran contained larger amounts of FAHFAs than FBRA, a traditional Asian food.•High level of oleic acid ester of 10‑hydroxy-12(Z)-octadecenoic acid was observed.•FBRA contains a higher amount of FAHFAs than cereals, vegetables, fruits and meat.•The presence of FAHFAs may prevent insulin resistance and chronic inflammation. Fermented brown rice and rice bran with Aspergillus oryzae (FBRA) is a processed food known to have anti-inflammatory and anti-tumorigenic effects. Moreover, suppressive effects on spontaneous type-1 diabetes have recently been reported in mice. The determination of the active ingredients in FBRA is crucial to explain its health benefits. We investigated the presence of branched saturated fatty acid esters of hydroxyl fatty acids (FAHFAs) in rice bran and FBRA by liquid chromatography-tandem mass spectrometry (LC-MS/MS) using commercially available and custom-synthesized standards. FAHFAs are novel bioactive lipids that exhibit anti-diabetic and anti-inflammatory effects. A possible involvement in cancer prevention has also been suggested. The FAHFA profiles differed between rice bran and FBRA both qualitatively and quantitatively. Interestingly, in both samples, the quantity of branched saturated FAHFAs was much higher than that previously reported for other cereals, vegetables and fruits. Therefore, given the beneficial effects of FAHFAs, regular consumption of FRBA may prevent metabolic disorders, insulin resistance, and chronic inflammatory disorders.