Effects of mineral addition on the growth morphology of and arachidonic acid production by Mortierella alpina 1S‐4

The culture conditions for arachidonic acid (AA) production by Mortierella alpina 1S‐4 were investigated by means of a morphological study with the aims of obtaining a high AA yield and scale‐up. In a 50‐L jar fermentor study, a medium containing 3.1% soy flour and 1.8% glucose with 0.3% KH 2 PO 4 , 0.1% Na 2 SO 4 , 0.05% CaCl 2 ·2H 2 O and 0.05% MgCl 2 ·6H 2 O was found to be optimum. The AA yield reached 9.8 g/L/7 d, and the major morphology was small pellets (1–2 mm). However, in the case of the only addition of KH 2 PO 4 , the major morphology was filaments. The apparent viscosity increased to 2240 cp, thereby requiring a high agitation speed to maintain adequate oxygen tension, which caused mycelial damage due to shear stress and therefore a decrease in the AA yield. When a medium with Na 2 SO 4 , CaCl 2 , and MgCl 2 was used, the major morphology was large pellets (2–3 mm), and mass transfer limitation through the pellet wall caused a decrease in the AA yield. Based on these results, a scale‐up study was carried out under the optimal conditions described above. An AA yield of 10.9 g/L/8 d was obtained in a 10‐kL industrial fermentor, and the major morphology was small pellets.