A wild-type A. niger strain was employed as a model to investigate the effect of cell immobilization on extracellular
protease secretion during fermentation. A metal-coated pad of polyester latex felt was used to immobilize the cells in
shake flasks. Compared with free suspension culture, the maximum specific activity of the extracellular protease from
immobilized cells was reduced from 129 units/g to 28 units/g.