title: Application of Fourier transform infrared spectroscopy and orthogonal projections to latent structures/partial least squares regression for estimation of procyanidins average degree of polymerisation.
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. FTIR 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 in the aromatic ring of the polymerised procyanidin molecules.
authors.affiliation: CICECO, Departamento de Química, Universidade de Aveiro, 3810-193 Aveiro, Portugal.
authors.forename: Cláudia P
authors.initials: CP
authors.lastname: Passos
authors.forename: Susana M
authors.initials: SM
authors.lastname: Cardoso
authors.forename: António S
authors.initials: AS
authors.lastname: Barros
authors.forename: Carlos M
authors.initials: CM
authors.lastname: Silva
authors.forename: Manuel A
authors.initials: MA
authors.lastname: Coimbra
mesh_terms: D044946:Biflavonoids / Q000737:chemistry* / Q000302:isolation & purification; D002138:Calibration; D002392:Catechin / Q000737:chemistry* / Q000302:isolation & purification; D002725:Chloroform / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D005612:Freeze Drying; D016018:Least-Squares Analysis; D000432:Methanol / Q000737:chemistry; D011108:Polymers / Q000737:chemistry*; D025341:Principal Component Analysis; D044945:Proanthocyanidins / Q000737:chemistry* / Q000302:isolation & purification; D015203:Reproducibility of Results; D012639:Seeds / Q000737:chemistry; D012995:Solubility; D017550:Spectroscopy, Fourier Transform Infrared; D027843:Vitis / Q000737:chemistry
chemical_list: D044946:Biflavonoids; D011108:Polymers; D044945:Proanthocyanidins; C017674:procyanidin; D002725:Chloroform; D002392:Catechin; D000432:Methanol