Real time and in situ Near-Infrared Spectroscopy (Nirs) for Quantitative Monitoring of Biomass, Glucose, Ethanol and Glycerine concentrations in an alcoholic fermentation

This study investigates the application of NIR spectroscopy for real-time monitoring of process parameters in alcoholic fermentations. For this purpose, fermentation batches using Saccharomyces cerevisiae were carried out and monitored in situ by an immersed NIRS probe. Samples were collected throughout the fermentations, and concentrations of biomass, glucose, ethanol and glycerin were analyzed by reference methods and multivariate data analyses such as PCA and PLSR. PCA was used to investigate data variability and to select samples for calibration and for external validation sets. A PLSR model for biomass yielded R-2 and RMSEP values of 0.99 and 0.276 g.L-1, respectively. For glucose, the carbon source, the PLSR model yielded an R-2 of 0.95 and an RMSEP of 7.14 g.L-1. The PLSR model for ethanol was characterized by an R-2 of 0.95 and an RMSEP of 0.06 g.L-1. For glycerin, a highly accurate PLSR model with an R-2 of 0.98 and an RMSEP of 0.116 g.L-1 was obtained. These results indicate that an in situ NIRS probe is suitable for real-time monitoring of important parameters in alcoholic fermentations.