Association of non-starch polysaccharides and ferulic acid in grain amaranth (Amaranthus caudatus L.) dietary fiber

Abstract

The association of ferulic acid, an alkali-extractable phenolic acid in amaranth (Amaranthus caudatus L., Amaranthaceae) insoluble fiber (trans-ferulic acid: 620 microg.g-1, cis-ferulic acid: 203 microg.g-1), and non-starch polysaccharides was investigated. Enzymatic hydrolysis of insoluble amaranth fiber released several feruloylated oligosaccharides that were separated using Sephadex LH-20-chromatography and reversed phase-high performance liquid chromatography (RP-HPLC). Three compounds were unambiguously identified: O-(6-O-trans-feruloyl-beta-D-galactopyranosyl)-(1-->4)-D-galactopyranose, O-(2-O-trans-feruloyl-alpha-L-arabinofuranosyl)-(1-->5)-L-arabinofuranose, and O-alpha-L-arabinofuranosyl-(1-->3)-O-(2-O-trans-feruloyl-alpha-L-arabinofuranosyl)-(1-->5)-L-arabinofuranose. These feruloylated oligosaccharides show that ferulic acid is predominantly bound to pectic arabinans and galactans in amaranth insoluble fiber. 5-O-trans-Feruloyl-L-arabinofuranose was the only compound isolated in pure form from an acid hydrolyzate. This compound may have its origin from pectic arabinans but also from arabinoxylans.