abstract
Fourier transform infrared (FTIR) spectroscopy has being emphasised as a widespread technique in the quick assess of food components. In this work, procyanidins were extracted with methanol and acetone/water from the seeds of white and red grape varieties. A fractionation by graded methanol/chloroform precipitations allowed to obtain 26 samples that were characterised using thiolysis as pre-treatment followed by HPLC-UV and MS detection. The average degree of polymerisation (DPn) of the procyanidins in the samples ranged from 2 to 11 flavan-3-ol residues. MR spectroscopy within the wavenumbers region of 1800-700 cm(-1) allowed to build a partial least squares (PLS1) regression model with 8 latent variables (LVs) for the estimation of the DPn, giving a RMSECV of 11.7%, with a R(2) of 0.91 and a RMSEP of 2.58. The application of orthogonal projection to latent structures (O-PLS1) clarifies the interpretation of the regression model vectors. Moreover, the O-PLS procedure has removed 88% of non-correlated variations with the DPn, allowing to relate the increase of the absorbance peaks at 1203 and 1099 cm(-1) with the increase of the DPn due to the higher proportion of substitutions ill the aromatic ring of the polymerised procyanidin molecules. (C) 2009 Elsevier B.V. All rights reserved.
keywords
ELECTROSPRAY MASS-SPECTROMETRY; RED WINE TANNINS; GRAPE SEEDS; MIDINFRARED SPECTROSCOPY; QUANTITATIVE-ANALYSIS; PHENOLIC-COMPOUNDS; CROSS-VALIDATION; PLS-REGRESSION; PROANTHOCYANIDINS; APPLE
subject category
Chemistry
authors
Passos, CP; Cardoso, SM; Barros, AS; Silva, CM; Coimbra, MA
our authors
António de Sousa Barros
Post-doc Fellowship
Carlos Manuel Silva
Associate Professoracknowledgements
The authors gratefully acknowledge Pedro Vasco (Universiclade de Aveiro) and Eng. A. Dias Cardoso, Eng. Jos. Carvalheira, and all staff from Estacao Vitivinicola da Bairrada, Portugal, for the technical support and raw material provided. Thanks are also due to Adega Cooperativa de Pinhel for providing the seed from red grapes. This work was supported by the Research Unit 62/94 QOPNA and project POCTI/EQU/47533/2002. Claudia Passos was supported by a PhD grant by FCT, SFRH/BD/19072/2004.