Production of gluconic acid from whey by free and immobilized Aspergillus niger

Deproteinized whey has been used as a fermentation medium for the production of gluconic acid by Aspergillus niger immobilized in polyurethane foam or free cells. Addition of a small amount of glucose (0.5%, w/v) in the whey medium enhanced the production of gluconic acid by 140% over the unsupplemented medium. Immobilized mycelia produced 92 g of gluconic acid from 1 L of whey medium containing 9.5% lactose and 0.5% glucose against 69 g by free mycelia. Immobilized mycelia can be reused.