Comparative Studies on Citric Acid Fermentation by Parent and Mutant Aspergillus niger From Some Agricultural Wastes Using Submerged Fermentation

Abstract

Citric acid fermentation by parent and mutant Aspergillus niger from some agro-industrial wastes (wheat bran, rice bran and orange pulp) was studied. The study involved the improvement of a cellulase producing A. niger isolate by exposure to ultraviolet irradiation for 45 minutes using Phillips germicidal lamp, the selection of mutant based on the method of Kubicek et al. (1986) and citric acid fermentation from the aforementioned agroindustrial wastes by the selected mutant and the parent isolate using submerged fermentation. The results obtained show that submerged fermentation of orange pulp by mutant A. niger produced the highest yield of 14. 70g/l. Other yields obtained in descending order are, 13. 78g/1 obtained from fermentation of wheat bran by mutant A. niger, 12. 39g/1 obtained from fermentation of orange pulp by parent, 11.85gl1 obtained from fermentation of rice bran by mutant A. niger, 9.27g11 obtained from fermentation of wheat bran by parent A. niger and 9.08g/1 obtained from fermentation of rice bran by parent A. niger. The average length of fermentation that gave the highest citric acid yield was 144h (six days). In all cases the mutant A. niger produced more citric acid than the parent A. niger. However, more citric acid was produced from orange pulp by parent A. niger than from rice bran by mutant A. Niger