Structural variation and levels of water-extractable arabinogalactan-peptide in European wheat flours

Water-extractable arabinogalactan-peptides (WE-AGP) were isolated from flour of eight different wheat cultivars (harvest year 1996). Little structural variation in WE-AGP of flour of the different wheat cultivars was observed. The arabinose-to-galactose (A/G) ratio of WE-AGP varied between 0.66 and 0.73. Methylation analysis showed that the proportion of beta-1,3-galactopyranosyl residues is almost equal for the different WE-AGP samples (10.2-11.1%). More variation was observed for the proportion of the beta-1,6-galactopyranosyl residues (9.4-13.0%) and beta-1,3,6-galactopyranosyl residues (76.0-80.1%). The H-1-nuclear magnetic resonance spectra (D2O, 85 degrees C, 300 MHz) were comparable, and gel permeation analysis consistently yielded a narrow peak with an apparent molecular weight between 5.0 x 10(4) and 10.0 x 10(4). Interpretation of the results was facilitated by alpha-L-arabinofuranosidase debranching of WE-AGP. For flour samples of 18 wheat cultivars (10 from 1994 harvest, eight from 1996 harvest), the variation in percentage of water-extractable arabinoxylan (WE-AX) (0.31-0.78% of dry matter) was much larger than the variation in percentage of water-extractable arabinogalactan (WE-AG) (0.24-0.33%). The ratio of WE-AX to WE-AG for flour samples of different wheat cultivars varied between 1.00 and 2.44.