Diffuse reflectance Fourier transform infrared spectroscopy for simultaneous quantification of total phenolics and condensed tannins contained in grape seeds

Abstract

Total phenolic and condensed tannin contents of grape seeds were simultaneously quantified using diffuse reflectance Fourier transform spectroscopy and partial least squares (PLS). The results were compared with those obtained using the conventional methods. Infrared spectra were recorder in solid state samples after freeze drying. The second derivative of the 1560–1177cm−1 spectral region was used for total phenolic determination. The determination coefficient (R2) was 0.97, the root-mean-square error of calibration (RMSEC) 4.03, and the root-mean-square error of prediction (RMSEP) 6.49. For the condensed tannin content, the 2nd derivative of the spectral regions 1670–950 (R2=0.99; RMSEC=7.01; RMSEP=10.13) and 3750–2125cm−1 (R2=0.99; RMSEC=2.65; RMSEP=3.97) was correlated with the concentration estimated by means of methylcellulose and bovine serum albumin assays, respectively. The proposed method in comparison with the conventional methods is simpler, less time consuming, more economical, and requires reduced quantities of chemical reagents and less sample processing prior to analysis. This might by a valuable tool for wine industry where the quantification of grape tannins in a large number of samples remains a priority.