Abstract
[Objective] Fermentation of rice bran with Aspergillus oryzae increases ceramides (Cer), but little is known about the chemical structure and biological activity of each molecular species. Therefore, we clarified the structure of Cer species contained in fermented rice bran and investigated their in vitro biological activities. [Method] After solid culture by adding A. oryzae and kojiang to rice bran, the Cer profile was analyzed by LC-MS/MS. Various glucosylceramides (GlcCer) and Cer were isolated by reversed phase HPLC, and their chemical structures were identified. Biological activity was evaluated using transepidermal water loss (TEWL) in a three-dimensional epidermal culture system, melanin production in B16 melanoma, and IL-6 production in dendritic cells as indicators. [Results and discussion] Fermentation increased Cer by 8 times and GlcCer by 2 times. The majority of Cer was Cer[t18:0] type, but Cer[d19:2] type was also detected. In GlcCer, the GlcCer[d19:2] type increased fivefold. Furthermore, mannoinositol phosphorylceramides (MIPC), which has a phosphate group, inositol, and mannose attached to Cer[d19:2], was also detected. Isolated compounds include Cer[t18:0/22:0] to Cer[t18:0/26:0], GlcCer[d19:2(4E,8E)/18:1] and GlcCer[d19:2(4E, 8E)/18:0]. Among these compounds, Cer[t18:0/23:0], Cer[t18:0/24:0] and GlcCer[d19:2(4E,8E)/18:1] showed a decrease in TEWL. Only Cer[t18:0/24:0] suppressed melanogenesis, and Cer[t18:0/24:0] and Cer[t18:0/25:0] induced IL-6 release from dendritic cells. These results reveal that koji mold-fermented rice germ contains multiple Cer species with different biological activities.
