Structural Variation and Levels of Water‐Extractable Arabinogalactan‐Peptide in European Wheat Flours

Abstract

ABSTRACTWater‐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 β‐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 β‐1,6‐galactopyranosyl residues (9.4–13.0%) and β‐1,3,6‐galactopyranosyl residues (76.0–80.1%). The 1H‐nuclear magnetic resonance spectra (D2O, 85°C, 300 MHz) were comparable, and gel permeation analysis consistently yielded a narrow peak with an apparent molecular weight between 5.0 × 104 and 10.0 × 104. Interpretation of the results was facilitated by α‐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.