Abstract
Diet is one of the critical factors that govern the human gut microbiome. Fermented foods provide beneficial effects for human health by supplying diverse nutrients and digestive enzymes. We aimed to investigate the effect of fermented rice extract prepared with Aspergillus oryzae on the growth of human symbiotic Faecalibacterium prausnitzii. After steamed rice was fermented by A. oryzae, a water-soluble fraction was prepared by centrifugation and used as rice-koji extract. The growth of F. prausnitzii in the media supplemented with 1% rice-koji extract was enhanced compared to that in a control medium. Fractionation of the rice-koji extract with an anion-exchange column and mass spectrometry analysis were conducted to identify the growth-promoting factors for F. prausnitzii. LC-MS/MS analysis revealed that the fractions showing a growth-promoting effect were rich in α-amylase from A. oryzae. The addition of purified A. oryzae-derived α-amylase and starch to the culture media increased the growth and butyrate production from F. prausnitzii. These findings suggest that A. oryzae-derived enzymes in fermented rice-koji possess a growth-promoting effect, enabling F. prausnitzii to efficiently uptake and utilize starch degradation products.