Carbon-13 cross-polarization magic-angle spinning nuclear magnetic resonance (CPMAS NMR) for measuring proanthocyanidin content and procyanidin to prodelphinidin ratio in sainfoin (Onobrychis viciifolia) tissues

Abstract

A procedure based on 13C CPMAS NMR was developed to study procyanidins (PCs) and prodelphinidins (PDs) directly in milled sainfoin plant tissues. Blackcurrant and Tilia samples enabled reference spectra of purified proanthocyanidin (PA) fractions, crude extracts and milled plant tissues, with characteristic resonances at 155, 144 and 132 ppm. PC/PD ratios were estimated from the I132/I155 intensity ratio and differed by 2.5 to 5.9% compared to thiolysis data. Normalization to the 155 ppm signal intensity from reference spectra enabled analysis of PA contents with an error of ca 8 g PAs/100 g plant tissue. The procedure estimates the lignin contribution and allows for a correction of the PA content. In six sainfoin accessions, estimated PA contents, were 1.6- to 20.8-fold higher than the thiolysis and 1.4- to 2.6-fold higher than the HCl-butanol-acetone results. Method differences may reflect the presence of unextractable, possibly high molecular weight PAs in sainfoin