Influence of a pulsed electric field on the spores and oxygen consumption of Aspergillus niger and its citric acid production

Spores of Aspergillus niger were exposed to a pulsed electric field. After treatment by the electric field, the viability of the conidia of A. niger v aried depending oil the field strength, pulse width and frequency. In all c ases, these parameters reduced the viability rate of the conidia from 2.0 x 10(7) to a range from 6.2 x 10(6) to 8.5 x 10(6) spores/ml (3.1 to 42.6%). After pulse treatment, the conidia were used as the inoculum for citric ac id fermentation in shake flasks;. The highest increase in citric acid yield (about 1.4-fold) was reached at a field strength of 2.85 kV/cm, a frequenc y of 1 Hz and a pulse width of 1 ms. When the parameters of the electric fi eld increased there were important changes in the respiration rate of the A spergillus niger mycelium (48-h-old) after electric shock treatment. The hi ghest consumption of dissolved oxygen (22.9%) in the medium by Aspergillus niger mycelium was observed at an electric field strength of 2.85 kV/cm, a 1 Hz frequency, a pulse width of 1 ms and a 1-min exposure period. It seems that an electric-field stimulation of the conidia prior to inoculation may offer an important method of improving the efficiency of citric acid. The treatment of the conidia is both simple from the technical point of view an d extremely rapid.