Real-time monitoring of xylitol production in a bioreactor by Candida tropicalis IEC5-ITV using Near-Infrared Spectroscopy (NIRS)

The use of Near-Infrared Spectroscopy (NIRS) and Chemometrics in-situ or in-line monitoring of xylitol fermentation process by Candida tropicalis IEC5-ITV was investigated in a bioreactor and in a complex analytical matrix. Xylose, xylitol, biomass and glycerol determinations were performed by a transflection fiber optic probe, immersed in the culture broth and connected to a Near-Infrared (NIR) process analyzer. The NIR spectra recorded between 800 and 2,200 nm, these NIR Spectra were pretreated using Savitzky-Golay smoothing and second derivative in order to perform a partial least squares regression (PLSR) and generate the calibration models. These calibration models were tested by external validation and then used to predict concentrations of xylitol fermentations in batch culture. The standard errors of calibration (SEC) and determination coefficients (R2) for xylose, xylitol, biomass and glycerol were 0.234 (R2 = 0.991), 0.220 (R2 = 0.999), 0.234 (R2 = 0.991) and 0.015 (R2 = 0.999) g/L and standard errors of prediction (SEP) were 1.771, 0.192, 0.011, 0.503 g/L, respectively. Calibration and validation criteria were defined and evaluated in order to generate robust and reliable models of a xylitol fermentation process. For validation models, SEV and SEP were < 10 % of initial concentration of xylose and R2 > 0.96 were obtained.  These results indicate that in situ NIRS probe is suitable for real-time monitoring of xylitol production.

Keywords: Near Infrared Spectroscopy (NIRS); xylose; Candida Tropicalis; real-time monitoring; xylitol.