Gluconic acid production at high concentrations by Aspergillus niger immobilized on a nonwoven fabric

Abstract

Batch production of gluconic acid in the presence of a high concentration of glucose was investigated using free and immobilized mycelia of Aspergillus niger IAM 2094 with the aim of achieving repeatable constant production. Accumulation of 300 g/ l of gluconate with a productivity of 60 g/ l·h was achievable by intermittent addition of powdered glucose using filamentous-form mycelia in the presence of 150 ppm dissolved oxygen. However, this productivity became unattainable after a few repetitions. The use of pellet-form mycelia, in place of filamentous ones, did not prove effective either. However, when the mycelia were immobilized on a nonwoven fabric, a sustained level (220 g/ l) of gluconate production was reproducible. Immobilized mycelia grown in a gas phase (air or oxygen) had a much longer durability than mycelia grown in a liquid culture medium. The gluconate-producing activity of immobilized mycelia grown in the presence of oxygen was much higher than that of mycelia grown in air. At 150 ppm dissolved oxygen, 220 g/ l of gluconate was repeatedly produced 14 times at a constant production rate in a period of about 1,000 h.