The development of rapid, accurate, and cost-effective technologies for process monitoring is highly desirable in the biofuels sector. Here, a technique based on the combination of Fourier transform mid-infrared (FT-MIR) spectroscopy and partial least-squares (PLS) regression was evaluated as a tool for real-time monitoring of the process for bioethanol production from sucrose by Saccharomyces cerevisiae. Industrial musts composed of juice and molasses of sugar cane and sweet sorghum juice were used in the fermentations. Considering the chemical complexity of the substrates, the PLS models presented excellent external validation results, with root-mean-square error of prediction (RMSEP) values of 0.54, 1.02, 0.66, 1.93, 0.50, and 1.64 g L −1 for sucrose, glucose, fructose, ethanol, glycerol, and cells, respectively. The findings demonstrated that FT-MIR spectroscopy can be applied for real-time monitoring of the process, with potential to reduce costs and provide accurate information for more efficient control of the process.

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BACKGROUND: Determination of the volumetric oxygen transfer coefficient (k L a) is very important for bioreactor design and process analysis. Among all the methods available, the gassing-out technique is one of the simplest and most widely used for this task. However, this method is very sensitive to the probe dynamics (due to delay effects), which can lead to inaccuracy in the k L a determination. This is especially pronounced for airlift bioreactors, where the circulation time affects the initial dynamics of the assay (a transient effect). In the present work, a new method for k L a determination is proposed.

The solid-liquid equilibrium of precursors and products of the enzymatic synthesis of ampicillin (AMP) [6-aminopencillanic acid (6-APA) and D(À)phenylglycine (PG)] was investigated at different temperatures (283-298 K) and pHs (5.5-7.5). Solubility data were obtained using an analytical methodology. Equilibrium dissociation constants were experimentally measured at several temperatures for AMP, 6-APA, PG, and D(À)phenylglycine methyl ester. A model based on the simplified perturbed hard sphere theory proposed by Khoshkbarchi and Vera (Ind Eng Chem Res. 1996;35:4319-4327) was fitted against solubility data. The model could describe the water solubility behavior for AMP and PG as function of pH and temperature, but a bias was observed when fitting the model to the solubility of 6-APA. V