Changes in the Phenolic Composition of Maize Stovers after Blooming

The phenolic composition of 10 samples of maize stovers collected every 7 days after blooming was determined by high-performance liquid chromatography with electrochemical detection (HPLC-ED) and pyrolysis/gas chromatography/mass spectrometry (PY/GC/MS). An increase of the p-hydroxycinnamic acids (i.e., p-coumaric acid and ferulic acid) with maturation was observed by HPLC-ED of mild alkaline extracts. Likewise, vanillin and syringaldehyde, i.e., the typical aldehydes constituting lignin, showed an increase with maturation in the alkali-soluble lignin fraction, as determined by HPLC-ED after nitrobenzene oxidation. As to PY/GC/MS, a less marked variation in the typical lignin units was observed with ripening. The ratios between syringyl and guaiacyl lignin units as determined by both analytical techniques were higher, but of the same order, than those determined previously in a set of maize stovers sampled over a wider range of maturation. Keywords: Maize stover; phenolics; lignin; high-performance liquid...