Near-infrared spectroscopy for bioprocess monitoring and control

This article describes the calibration of a spectroscopic scanning instrume nt for the measurement of selected contaminants in a complex biological pro cess stream. Its use is for the monitoring of a process in which contaminan ts are to be removed selectively by flocculation from yeast cell homogenate . The main contaminants are cell debris, protein, and RNA. A low-cost instr ument has been developed for sensitivity in the region of the NIR spectrum (from 1900 to 2500 nm) where preliminary work found NIR signatures from cel l debris, protein, and RNA. Calibration models have been derived using a mu ltivariate method for concentrations of these contaminants, such as would b e found after the flocculation process. Two strategies were compared for ca librating the NIR instrument. In one case, samples were prepared by adding materials representative of the contaminants to clarified yeast homogenate so the contaminant levels were well known but outside the range of interest . In the other case, where samples were like those from the process stream after flocculation and flee removal, there was uncertainty of analysis of c ontaminant level, but the calibration was in the range of interest. Calibra tion using process stream samples gave results close to those derived from traditional assays. When the calibration models were used to predict the co ntaminant concentrations in previously unseen samples, the correlation coef ficients between measurements and predictions were above 90% in all cases b ut one. The prediction errors were similar to the errors in the traditional assays. (C) 1999 John Wiley & Sons, Inc.