Microbial Production of Novel Pigments from Black Rice Anthocyanin

We screened soil microorganisms with the potential to modify the structure of black rice anthocyanin. After culturing the microorganisms on PDA medium containing black rice anthocyanin, caffeic acid, p-hydroxybenzoic acid, ferulic acid, and malonic acid for 4 days at 30°C, one strain that changed the red medium to reddish purple was isolated. Anthocyanins present in the color-changed medium were extracted using 15% (w/v) acetic acid and their absorption spectra were then determined. The analysis revealed that the peak wavelength of the extracted anthocyanins was shifted to a shorter wavelength (500 nm) from that of black rice anthocyanin (520 nm). Further HPLC separation of the anthocyanins confirmed that four new species were present in the medium. Of the four pigments, two showed an absorption maximum at 500 nm. Analysis of their basic structure by acid hydrolysis showed that the two pigments had clearly different retention times from cyanidin, which is the main anthocyanidin in black rice, and were not malvidin or peonidin. A 16S rDNA homology search indicated that the isolated microorganism with the ability to modify the structure of black rice anthocyanin was an Enterobacter aerogenes strain.