On-line monitoring of citric acid production in solid-state culture by respirometry

The aim of this work was to study the possibility of monitoring citric acid production from mussel processing
wastes (MPW) by Aspergillus niger in solid-state culture (SSC) on an inert support. This was conducted by
measuring CO2 and 02 concentration in exhaust gases, using an automatic sampler connected to a gas
chromatograph and a data acquisition system. The procedure permitted information on the physiological
state of the culture to be obtained. A relationship between citric acid accumulation and a decreasc in CO,
production was found, allowing citric acid production to be followed in real-time. Moreover, respiratory
activity (p,.) can be estimated and the effect of different variables on this parameter studied. Initial nitrogen concentration, a critical factor for achieving high production of citric acid from MPW in submerged culture revealed no effect in SSC. This indicates a tolerance of SSC to higher concentrations of nitrogen con-
stituting an advantage when using residual media with high levels of protein and wlriability in their
composition.