Hydroxycinnamic acids in walls of wheat aleurone cells

Walls were isolated from sheets of aleurone cells from wheat, freed from associated protein and starch by extraction with phenol-acetic acid-water followed by treatment with porcine pancreatic alpha-amylase, and finally extracted with sodium dodecyl sulphate. Hydroxycinnamic acids (HCA) released from the walls by saponification with 1 M NaOH amounted to 1.84% w/w of wall and comprised ferulic acid (90%), p coumaric acid (10%) and minor amounts (0.006%) of diferulic acids. The isolated walls exhibited an intense blue autofluorescence when irradiated with UV light that was reduced in intensity and became more diffuse after saponification. Acetyl residues (4.9% w/w) were present representing a degree of substitution of two in every nine pentose residues in the wall arabinoxylans. Digestion of the walls with a polysaccharide hydrolase mixture that lacked HCA esterases, released a series of oligomers that contained 50% of the total esterified HCA. These were separated by hydrophobic exclusion chromatography, purified by paper chromatography and two of these were identified by ES-MS and NMR as O-[5-O-feruloyl-alpha-L-arabinofuranosyl]-(1-->3)-O-beta-D-xylopyranosyl(1-->4)-beta-D-xylopyranose (FAXX) and O-beta-D-xylopyranosyl-(1-->4)-O-[5-O-feruloyl-alpha-L-arabinofuranosyl]-(1-->3)-O- beta-D-xylopyranosyl-(1-->4)- P-D-xylopyranose (XFAXX). The extremely low level of esterified diferulic acid indicates that cross-linking between polysaccharide chains by diester-FA is not important, however the esterified FA may play a role in cross-linking polysaccharides to wall proteins. (C) 2002 Elsevier Science Ltd.