Orange (pulp) and pineapple wastes were used as substrates for citric acid production by two strains of Aspergillus niger. A. niger strains NRRL 567 and 328 produced the maximum amount of citric acid (57.6% and 55.4%, respectively) at a moisture content of 38.9% in orange waste and the highest yields of 46.4% and 45.4% citric acid in pineapple waste at moisture contents of 54.4% and 63.4 %, respectively. The addition of 1-3% methanol to the substrates resulted in reduction in yield in both cases.
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