Validating a portable ad-hoc fluorescence spectrometer for monitoring phenolic compounds during wine fermentation

Abstract

Phenolic compounds are fundamental to wine quality, influencing its colour, mouthfeel, stability, and ageing potential [1]. Their extraction and evolution during fermentation plays a crucial role in determining the final sensory attributes and requires careful monitoring to guide winemaking decisions. Traditional analytical techniques such as high-performance liquid chromatography (HPLC) and UV-Vis spectrophotometry are well-established for phenolic quantification but are often impractical for real-time monitoring due to their time-intensive protocols and laboratory requirements. Fluorescence spectroscopy, with its high sensitivity and non-destructive nature, presents an attractive alternative [2]. However, commercially available instruments are not tailored to the unique challenges of winemaking, creating a gap in accessible and practical solutions for on-site monitoring.

This study validates a portable fluorescence spectrometer designed for the direct measurement of phenolic compounds in wine without the need for dilution or sample treatment. This capability allows for real-time monitoring of phenolic evolution throughout the entire fermentation process, providing rapid and reliable data directly from the wine matrix. The analytical performance of the spectrometer was evaluated in terms of its sensitivity, selectivity, repeatability, and robustness under winemaking conditions. A set of phenolic standards representing key wine polyphenols was used to assess figures of merit, including limit of detection (LOD), limit of quantification (LOQ), linearity, and reproducibility, all of which demonstrated strong analytical capabilities. Controlled fermentations with different grape musts were conducted, covering a range of phenolic profiles to test the instrument’s ability to differentiate and quantify relevant compounds. Fluorescence single excitation multiple emission matrices were generated and analysed through advanced chemometric methods, including Partial Least Squares Regression (PLSR) and other non-linear prediction algorithms [3]. These models enabled the accurate prediction of critical phenolic parameters such as total polyphenols, anthocyanins, and tannins, with particularly good performance observed in single cultivar specialized model fermentations, where spectral signals exhibited clearer correlations with reference phenolic measurements, achieving correlation coefficients higher than 80%.

The results highlight the potential of custom-designed ad-hoc analytical equipment as a game-changer for winemaking, offering a practical, efficient, and cost-effective alternative to traditional phenolic analysis. Unlike commercial fluorescence instruments adapted for general laboratory use, this tailor-made device is optimised for winery applications, enabling real-time decision-making without reliance on centralised facilities. Additionally, its versatile measuring chamber supports multiple configurations for diverse measurement needs and allows direct wine analysis without prior dilution, ensuring seamless integration into the production process as an effective process analytical technology. Its successful validation paves the way for a new paradigm in phenolic monitoring, empowering winemakers to enhance process control, refine blending and ageing strategies, and ultimately improve wine quality with greater precision and efficiency.

References

[1] Merkyte, V., Longo, E., Windisch, G., Boselli, E. (2020) Foods, 9(12), 1785.

[2] dos Santos, I., Bosman, G., Aleixandre-Tudó, J.L., du Toit, W. (2022) Talanta, 236, 122857.

[3] Cozzolino, D., Cynkar, W.U., Shah, N., Dambergs, R.G., Smith, P.A. (2009) International Journal of Wine Research, 1, 123-130.