“…In recent years citric acid has also been produced on a laboratory scale with Aspergillus niger cells immobilized on calcium alginate gel (Vaija, et al 1982;Rehm, 1984, 1987a;Vaija and Linko, 1986;Honecker, et al 1989), polyacrylamide gel (Horitsu, eta]. 1985; Garg and Sharma, 1992), and on polyurethane foam (Lee, et al, 1989;Vassilev and Vassileva, 1990). In addition, Kautola, et al (1991a) and Rymowicz, et al (1993) Aspergillus niger (Garg and Sharma, 1991) was used in this study.…”