Enhancement of anthocyanin production by Perilla frutescens cells in a stirred bioreactor with internal light irradiation

Oxygen supply and light irradiation exhibited significant influence on the production of anthocyanin (red pigments) by suspended cultures of Perilla frutescens cells in a 2.6-l aerated and agitated bioreactor with a six-flat-bladed turbine. When the initial volumetric oxygen transfer coefficient (k_La) value was below 10 h⁻¹ and light was not irradiated, the anthocyanin production was never over 0.6 g/l. By modification of a gas sparger, the oxygen supply capability of the bioreactor was remarkably improved, and 1.65 g/l of anthocyanin was obtained at an enhanced k_La value of 15.4 h⁻¹. Moreover, it was found that anthocyanin accumulation at a 0.2 vvm aeration rate was higher than that at 0.1 or 0.4 vvm in the modified bioreactor, with the other cultivation conditions kept the same. Light irradiation also significantly increased anthocyanin accumulation in the stirred reactor at a low k_La value, i.e. 9.9 h⁻¹. However, a combination of irradiation with a higher oxygen supply reduced the production of anthocyanin in the bioreactor.