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This study sought to assess the feasibility of using ultraviolet‐visible‐near infrared (UV‐VIS‐NIR) spectroscopy to monitor changes in total polyphenol index, color intensity and volumic mass, three indicators of quality during red wine fermentation. Samples (n = 68) collected from eleven tanks during fermentation were scanned in three types of quartz flow cells, path lengths 0.1, 2 and 50 mm, in the UV‐VIS‐NIR region (200–1,100 nm), using a fiber spectrometer system in transmission mode. Principal component analysis and partial least squares regression were used to interpret spectra and develop calibrations for predicting wine composition during fermentation. Models for the prediction of total polyphenol index displayed coefficients of determination (r2) ranging between 0.21–0.98, whereas values for the standard error of cross‐validation (SECV) ranged from 2.29 to 14.91, depending on the spectral region used. Values for the prediction of color intensity were: r2 = 0.56–0.98 and SECV = 0.43–1.88. Corresponding values for volumic mass were r2 = 0.31–0.94 and SECV = 8.71–30.20 g/dm3. These results suggest that UV‐VIS‐NIR spectroscopy using a miniature fiber optic spectrometer as a promising tool could be used as an alternative method for the rapid monitoring of quality parameters during red wine fermentation.PRACTICAL APPLICATIONS
The study develops ultraviolet‐visible‐near infrared calibrations to monitor changes in total polyphenol index, color intensity and volumic mass, main indicators of quality during red‐wine fermentation, taking into account and responding to the requirements of the enological industry that looks for a swift, efficient, economical and – particularly – nondestructive analytical technique for measuring quality parameters during fermentation process with a single instrument and in a matter of seconds, saving time and enhancing the decision‐making process. The work also evaluates the efficacy of a simple, efficient and low‐cost instrument that belongs to so called new near infrared spectroscopy (NIRS) generation, which are most suitable to be implemented for on‐line analysis in the winemaking industry. The results suggest that the miniature fiber optic NIR spectrometer is a promising tool for monitoring the red wine fermentation process, allowing the instantaneous prediction of the main parameters to be controlled. At the same time, suitable wavelengths for these parameters are also proposed according to x‐loading weights and regression coefficients.
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