Optimization of L‐malic acid production by Aspergillus flavus in a stirred fermentor

Publisher Website
Google Scholar
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 Fez+ 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 C4 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% CaCO3 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.

This publication has 23 references indexed in Scilit: