Assessment of the biochemical composition of oilseed rape (Brassica napus L.) C-13-labelled residues by global methods, FTIR and C-13 NMR CP/MAS

The biochemical composition of stems, pod walls and roots of oilseed rape ( Brassica napus L.) plants, grown in a growth chamber with two levels of N f ertiliser, was assessed by two global methods, i.e., serial extraction with the Van Soest's technique and temperature-programmed pyroanalysis (TP-Py). Statistical analysis of the effect of various parameters on the proportion of soluble components, hemicellulose, cellulose and lignin-like components in oilseed rape organs showed that the composition of plant materials depe nded on the N nutrition conditions during plant growth. Contents of soluble and hemicellulose fractions were affected by the technique used. Elsewhere , both global techniques resulted in similar proportions of skeletal cellul ose (respectively 41 and 36% in low and high N stems, 37 and 30% in low and high N pod walls, 32 and 29% in low and high N roots) and of lignin-like c omponents which ranged from about 7% in high N stems and pod walls to 16% i n low N roots. Spectroscopy by FTIR showed a significant band at 1650 cm(-1 ) (amide I in proteins) in the root material (organ with the lowest C/N rat io) and the absence of lignin-specific bands. Carbon distribution by C-13 N MR CP/MAS of labelled plants indicated that 60-64% was (cellulose + hemicel lulose)-C, close to the values obtained by global methods. The proportion o f aromatic-C (110-160 ppm) and phenolic ether was higher in roots than in s tems and pod walls. Organs from oilseed rape plants with higher N contents exhibited a larger proportion of C in the 171 ppm chemical shift attributed to the peptide bond. The concomitance of a high level of aromatic and prot einaceous components in roots would reveal the presence of tannin-protein c omplexes in addition with true lignin.