The use of non-invasive fluorescence spectroscopy to quantify phenolic content under red wine real-time fermentation conditions

Phenolic compounds play important roles in wine quality attributes such as colour, mouthfeel and ageing potential. The ability to monitor their extraction and implement appropriate vinification techniques relies on accurate phenolic analysis methods. Front-face fluorescence spectroscopy presents itself as a user-friendly, rapid and cost-effective alternative to other spectrophotometric methods. The main aim of the study was therefore to investigate the potential of fluorescence spectroscopy to directly measure phenolic content of red wine samples throughout red wine fermentations. Cabernet Sauvignon fermentations were monitored using fluorescence spectroscopy and UV–Visible spectrophotometry. Fermentation conditions were explored for their influence on the prediction accuracy of fluorescence-based regression models. The coefficient of correlation (R2val) and root mean square errors of validation (RMSEV) for models built using non-invasive spectral data obtained from unaltered samples were 0.96, 0.94 and 0.89 and 1.38 index units, 42.84 mg/L and 20.53 mg/L for total phenols (index units (IU)), total condensed tannins (mg/L), total anthocyanins (mg/L), respectively. Overall, the ability to obtain high quality spectra from unaltered samples simulating direct measurements from the fermentation vessel was demonstrated and holds potential for on-line automated systems or portable device applications.