Temperature Influence in Real-Time Monitoring of Fed-Batch Ethanol Fermentation by Mid-Infrared Spectroscopy

Fourier transform mid-infrared (FT-MIR) spectroscopy is a fast, accurate, and practical technique for the quantitative analysis of compounds during ethanol fermentation. However, it is very temperature sensitive. This study aimed to develop a methodology for the real-time monitoring of fed-batch ethanol fermentations, taking into account the thermal fluctuations in the industrial process (in the range 30–35 °C). The use of FT-MIR combined with partial least squares (PLS) regression was evaluated as a tool to quantify sucrose, glucose, fructose, ethanol, and glycerol. The PLS models, based on fermentations carried out at constant temperatures in the range from 26 to 36 °C, presented high correlation coefficients (R2) and low root-mean-square errors of cross-validation and prediction that were below 7% of the calibration ranges for all compounds. The good performance of the models demonstrated their suitability for accurate process monitoring, covering a wide range of thermal variations observed in industrial operations.