At-line determination of octanoic acid in cultivation broth--an electronic tongue (ET) feasibility study

Production monitoring of "natural" 2-heptanone from octanoic acid in an industrial fed-batch cultivation based on Penicillium roqueforti requires development of a method for determination of octanoic acid dissolved in the water phase. An electronic tongue array using six non-specific potentiometric sensors with solid inner contact, and a pH electrode, has been introduced by spiking octanoic acid to a substrate obtained from four different cultivations, representing variations in the relevant industrial matrix. Multivariate calibration was performed on acid concentrations spanning 0.65-20 mmol l(-1). Excluding the lowest concentration a global Partial Least Square regression model with a predicted versus measured correlation of 0.98 and a relative root mean square error of prediction of 5.1% (ln units) (RPD=5.5) signifies a highly acceptable prediction facility. This model was further tested by subjecting it to undiluted as well as diluted samples obtained from a cultivation process in which octanoic acid was catabolized; this led to acceptable prediction errors within the same range as for the global model. It is concluded that the ET sensor array can be applied for determination of octanoic acid in cultivation systems of the general P. roqueforti type.