Title: Demethylation of a model homogalacturonan with a citrus salt-independent pectin methylesterase: Effect of pH on block size and number and resulting functionality Authors
Submitted to: National Meeting of Institute of Food Technologists/Food Expo
Publication Type: Abstract Only
Publication Acceptance Date: April 13, 2007
Publication Date: April 23, 2007
Citation: Luzio, G.A., Cameron, R.G. 2007. Demethylation of a model homogalacturonan with a citrus salt-independent pectin methylesterase: Effect of pH on block size and number and resulting functionality. National Meeting of Institute of Food Technologists/Food Expo. Presentation No. 137-03. Technical Abstract: A demethylation series with predicted degrees of methylesterification (DM) of 90, 80, 70, 60 and 50 % was produced from a model homogalacturonan (HG) by reacting it with a citrus salt-independent pectin methylesterase (PME) at pH 4.5 and 7.5. HG structural properties were probed by performing a limited digest with an endo-polygalacturonase (EPG) to excise demethylated blocks (DEMB) of galacturonic acid (GA). HPAEC coupled to an evaporative light scattering detector was used to separate and quantify the EPG liberated DEMBs. Functionality of the demethylated HGs was determined using the Calcium Sensitive Pectin Ratio (CSPR) and the rheological properties of Yield Point (YP) and Storage Modulus (G'). A significant increase in maximum (GAn) and average block size (B) of released DEMBs was observed between 80 % (GA14, B=5.3) and 70 % DM (GA42, B=10.2) at pH 7.5 and between 70 % (GA19, B=5.3) and 60 % (GA43, B=7.9) at pH 4.5. DEMBs > GA50 were observed in the pH 4.5 series at 50 % DM. While was greater in the pH 7.5 series, the average number of blocks per molecule was greater in the pH 4.5 series. Functionality, i.e. CSPR and rheological properties, was shown to be dependent on demethylation pH as well as DM. At pH 7.5 and 70 % DM the values for CSPR, YP and G' were 0.8 %, 0.042 Pa and 0.017 Pa respectively. At pH 4.5 and 70 % DM these values were 11.4 %, 0.171 Pa and 1.06 Pa respectively. The results suggest this PME may possess a variably processive mode of action, becoming more processive as the DM decreases, and that both size and number of DEMBs per molecule need to be considered for relating fine structure to functionality.