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Optimization of L ‐malic acid production by Aspergillus flavus in a stirred fermentor
Author(s) -
Battat Emil,
Peleg Yoav,
Bercovitz Amir,
Rokem J. Stefan,
Goldberg Israel
Publication year - 1991
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/bit.260371117
Subject(s) - malic acid , fumaric acid , fermentation , succinic acid , chemistry , aspergillus flavus , malic enzyme , fumarase , biochemistry , malate dehydrogenase , citric acid , food science , dehydrogenase , enzyme
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 m M ) 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.