Phenolic profiling of grapes, fermenting samples and wines using UV-Visible spectroscopy with chemometrics

- Robust UV-VIS calibrations for phenolic compositional analysis are proposed.
- Accurate PLS models have been reported for grapes, fermenting samples and wines.
- Slope and intercept test, interclass correlation coefficients and SEM are investigated.
- Limit of detection and limit of quantification of the PLS models are evaluated.
- UV-VIS spectroscopy as an alternative to IR for process control during the winemaking.

Phenolic compounds play and important role on colour, flavour and mouthfeel attributes of wines. The acquisition of information related to phenolic compounds during the winemaking process is therefore becoming a necessity. Ultraviolet-Visible (UV-Vis) spectroscopy appears as an affordable option to monitor phenolic composition and levels during winemaking. To investigate this, a large number of samples collected from industrial fermentations over two vintages as well as commercial wine samples, spanning a wide range of vintages, were analysed for phenolic compounds using high performance liquid chromatography (HPLC). Methyl cellulose precipitable (MCP) tannins, anthocyanins, total phenols and colour density were also analysed. Partial least-squares (PLS) calibration models, based on UV-VIS spectra and reference measurements, were constructed and their performance evaluated in terms of the residual predictive deviation values. The accuracy and robustness of the calibrations were further evaluated by a combined test on slope and intercept, interclass correlation coefficients and standard error of measurement. Limit of detection and limit of quantification of the PLS models were also reported and evaluated. Furthermore, PLS models for an additional data set including 130 grape samples was also investigated for MCP tannins, anthocyanins, total phenols and colour density measurements. Phenolic compounds were extracted following two different protocols, namely wine-like and homogenate methods.