Feasibility study of FT-MIR spectroscopy and PLS-R for the fast determination of anthocyanins in wine

The feasibility of using Fourier Transform Mid-Infrared Spectroscopy (FT-MIR) combined with Partial Least Squares Regression (PLS-R) for the determination of 12 anthocyanins (3-O-glucosides of delphinidin, cyanidin, petunidin, peonidin and malvidin, as well as acetic acid esters and p-coumaric acid esters of petunidin, peonidin and malvidin and caffeic acid ester of malvidin) and three sums (sum of non-acylated anthocyanins, sum of acetylated anthocyanins and sum of coumaroylated anthocyanins), in red wines has been tested. Reference values of anthocyanin concentrations by reverse-phase High Performance Liquid Chromatography with Diode Array Detection (HPLC-DAD) were used to calibrate the models. A Principal Component Analysis (PCA) was applied to these reference values and a differentiation of wine samples by wine type (young wines of 2005, young wines of 2004 and crianza and reserva wines) has been possible. A calibration model using PLS-R was built with 153 samples of Rioja wines and the prediction of the anthocyanin concentrations using this model was evaluated by internal and external validation sample sets. Most of the anthocyanins and their sums have been predicted with a Standard Error of Prediction (SEP) of 15-30% for young wines recently bottled. However, for young wines after one year of being bottled, and for crianza and reserva wines, these errors were unacceptable. The obtained results suggest that the model built for FT-IR instrument calibration is a useful tool for a quick determination of the anthocyanin content of young wines of the current vintage, but a careful robust external validated calibration of the technique is necessary in order to maintain the prediction errors within controlled limits.