Effect of transition metal cations and anions on the production of citric acid by <i>Aspergillus niger</i>

Abstract

<span style="font-size:14.0pt;font-family:" times="" new="" roman";color:black;mso-bidi-font-weight:="" bold"="" lang="EN-IN">Interest in studying the effect of microelements on the metabolism of fungi during the bioconversion has led to this work. The present work reports the production of citric acid starting from glucose by <i>Aspergillus niger. </i>The

<span style="font-size:14.0pt;font-family:" times="" new="" roman";color:black;mso-bidi-font-weight:="" bold"="" lang="EN-IN">microelements supplemented were cadmium, lead, chromium and molybdenum. The bioconversion path of <i>Aspergillus niger </i>was TCA cycle. The products of the microbial metabolism namely total titrable acidity, citric acid, succinic acid, malic acid, intracellular proteins, extracellular proteins, amylase activity, lipid and biomass contents were determined periodically. Among the nutritional supplements tried cadmium was found to drive the metabolism of <i>Aspergillus niger </i>to produce more amount of citric acid. Experimentally observed growth stages were used for mathematical modelling to explore kinetic parameters. The values calculated based on the model were found to agree well with the observed ones in the case of lead and cadmium as supplements, whereas in the case of molybdenum and chromium deviations occur between the calculated and observed values. This discrepancy in the values of metabolic products was ascribed to the <i>p</i>H<i>, </i>temperature and other inhibitory products formed during fermentation.

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