ARS | Publication request: Citrus salt-independent pectin methylesterase demethylation of a model homogalacturonan: effect of pH on demethylated block size and distribution

Submitted to: Subtropical Technology Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: September 11, 2006
Publication Date: October 18, 2006
Citation: Cameron, R.G., Goodner, K.L., Luzio, G.A. 2006. Citrus salt-independent pectin methylesterase demethylation of a model homogalacturonan: effect of pH on demethylated block size and distribution. Subtropical Technology Conference Proceedings. 57:15.

Technical Abstract: Multiple forms of pectin methylesterase (PME) purified from citrus have been shown to have a differential affect on citrus juice cloud leading to the hypothesis that they have different modes of action on pectin. PME hydrolyzes methyl esters on C6 of galacturonic acid residues in the homogalacturonan regions of pectin. Both the degree of esterification and the spatial distribution of the methyl esters have been shown to affect pectin functional properties. To test the hypothesis that the citrus PMEs can be used to produce pectins with tailored functional properties, we have initiated a program to create a series of demethylated pectins with each of the PMEs and to map their structure. These pectins also are being used to determine their corresponding functional properties. Initial studies have focused on the salt-independent PME from citrus. A pectin with an initial degree of esterification (DE) of 94% was demethylated to 90, 80, 70, 60 and 50% DE at pH 7.5 and 4.5. A minimum estimate of the size of the demethylated blocks was obtained by lightly digesting the pectins with endo-polygalacturonase. HPAEC coupled to an evaporative light scattering detector provided data on the distribution of sizes and amounts of the demethylated blocks. At pH 7.5 demethylated block size jumped from 19 to 47 when the DE dropped from 80% to 70%. At pH 4.5 a similar change occurred between a DE of 70% and 60%. Compared to pH 7.5 there were more small demethylated blocks present in the pH 4.5 demethylated pectins. At a DE of 70% the average block size was 11 in the pH 7.5 pectin but only 5 in the pH 4.5 pectin. The average number of blocks was higher in the pH 4.5 material. These results suggest pectin functionality can be manipulated by enzymatic treatment under controlled conditions.