Real time monitoring of multiple components in wine fermentation using an on-line auto-calibration Raman spectroscopy

In this paper, the novel technique for monitoring time-related changes that occur during wine fermentation, associated with auto-calibration Fourier transform Raman spectroscopy (FT-RS) and chemometric data analysis, was investigated. The auto-calibration system, which is composed of a reference optical path and measurement optical path, is first presented in this paper. The reference optical path was used to eliminate the frequency shift and intensity shift of the Raman spectra induced by the ambient temperature. The micro-fermentation trials conducted in our laboratory during 2013 were monitored by the auto-calibration FT-RS and by high-performance liquid chromatography (HPLC). Principal component analysis (PCA) and Partial least square (PLS) were applied to the Raman spectra to determine the relationship between the spectra and the concentration of sugar or alcohol during the fermentation process. The results from the PLS-PCA and HPLC showed good correlations and were obtained between predicted and actual sample values for sugar (0.995), ethanol (0.9999), and glycerol (0.98). The experimental results showed that the auto-calibration FT-RS is useful to identify crucial information about the quality of the final product in agreement with the chemical analyses during wine fermentation.