title: Optimization of L-malic acid production by Aspergillus flavus in a stirred fermentor.
abstract: Effects of various nutritional and environmental factors on the accumulation of organic acids (mainly L-malic acid) by the filamentous fungus Aspergillus flavus were studied in a 16-L stirred fermentor. Improvement of the molar yield (moles acid produced per moles glucose consumed) of L-malic acid was obtained mainly by increasing the agitation rate (to 350 rpm) and the Fe(z+) ion concentration (to 12 mg/L) and by lowering the nitrogen (to 271 mg/L) and phosphate concentrations (to 1.5 mM) in the medium. These changes resulted in molar yields for L-malic acid and total C(4) acids (L-malic, succinic, and fumaric acids) of 128 and 155%, respectively. The high molar yields obtained (above 100%) are additional evidence for the operation of part of the reductive branch of the tricarboxylic acid cycle in L-malic acid accumulation by A. flavus. The fermentation conditions developed using the above mentioned factors and 9% CaCO(3) in the medium resulted in a high concentration (113 g/L L-malic acid from 120 g/L glucose utilized) and a high overall productivity (0.59 g/L h) of L-malic acid. These changes in acid accumulation coincide with increases in the activities of NAD(+)-malate dehydrogenase, fumarase, and citrate synthase.
authors.affiliation: Department of Applied Microbiology, Institute of Microbiology, The Hebrew University, PO Box 1172, Jerusalem 91010, Israel.
authors.forename: E
authors.initials: E
authors.lastname: Battat
authors.forename: Y
authors.initials: Y
authors.lastname: Peleg
authors.forename: A
authors.initials: A
authors.lastname: Bercovitz
authors.forename: J S
authors.initials: JS
authors.lastname: Rokem
authors.forename: I
authors.initials: I
authors.lastname: Goldberg