Cell wall polysaccharide interactions in maize bran

Abstract

Sequential extractions with alkali have been carried out in order to study the nature of linkages which hold heteroxylans in maize bran cell walls. Treatment with 0.5 m sodium hydroxide at 30 °C for 2 h released all the phenolic acids ( p-coumaric, ferulic, and diferulic) but extracted only ~30% of heteroxylans (S 1); further treatment with 1.5 m potassium hydroxide at 100 °C for 2 h released the remaining heteroxylans (S 2). The heteroxylans from S 1 and S 2 had a similar neutral sugar composition and structure, but their weight average molecular weights were 270 kDa ( M w M n = 2 ) and 370 kDa ( M w M n = 2.8 ), respectively. Proteins (5%) are found with polysaccharides from S 1 and S 2, with different amino acid composition. The results suggest that covalent linkages through phenolic acids are only partly responsible for the associations of maize bran heteroxylans in the cell wall and that linkages to structural cell wall proteins were probably the main cause of heteroxylan insolubility.