ONLINE MONITORING OF CITRIC-ACID PRODUCTION IN SOLID-STATE CULTURE BYRESPIROMETRY

The aim of this work was to study the possibility of monitoring citric acid production from mussel processing wastes (MPW) by Aspergillus ni ger in solid-state culture (SSC) on an inert support. This was conduct ed by measuring CO2 and O-2 concentration in exhaust gases, using an a utomatic sampler connected to a gas chromatograph and a data acquisiti on system. The procedure permitted information on the physiological st ate of the culture to be obtained. A relationship between citric acid accumulation and a decrease in CO2 production was found, allowing citr ic acid production to be followed in real-time. Moreover, respiratory activity (mu(r),) can be estimated and the effect of different variabl es on this parameter studied. Initial nitrogen concentration, a critic al factor for achieving high production of citric acid from MPW in sub merged culture, revealed no effect in SSC. This indicates a tolerance of SSC to higher concentrations of nitrogen constituting an advantage when using residual media with high levels of protein and variability in their composition. (C) 1998 Elsevier Science Ltd. All rights reserv ed.