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Title: Enzymatic modification of a model homogalacturonan with the thermally tolerant pectin methylesterase from citrus: I. Nanostructural characterization, enzyme mode of action and effect of pH

Author
item Cameron, Randall - Randy
item Luzio, Gary
item SAVARY, BRETT - Arkansas State University
item VASU, PRASANNA - Arkansas State University
item WILLIAMS, MARTIN - Massey University

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2011
Publication Date: 3/2/2011
Citation: Cameron, R.G., Luzio, G.A., Vasu, P., Savary, B.J., Williams, M.A.K. 2011. Enzymatic modification of a model homogalacturonan with the thermally tolerant pectin methylesterase from citrus: I. Nanostructural characterization, enzyme mode of action and effect of pH. Journal of Agricultural and Food Chemistry. 59:2717-2724.

Interpretive Summary: The mode of action of the citrus thermally tolerant pectin methylesterase appears to have limited processivity, on average producing only relatively small demethylesterified blocks (of negative charge) in a model system. The size of these charged blocks produced by the enzyme was dependent on the pH of the reaction and the final degree of methylesterification. Block sizes could be introduced by manipulating both pH and endpoint degree of methylesterification so that an optimized process could be engineered to achieve the desired structural/functional properties. The number of blocks per molecule also could be manipulated providing for an opportunity to tailor both structure and functionality. This flexibility has the potential to eliminate potential problems that might be associated with undesirable pHs such as side reactions or corrosion. The ability to produce designer pectins for use in food formulation or in-situ texture modification could provide new opportunities for the food industry.

Technical Abstract: Methyl ester distribution in pectin homogalacturonan has a major influence on functionality. Enzymatic engineering of pectin nanostructure for tailoring functionality can expand pectin’s role as a food formulating agent and its in situ modification in prepared foods. We report on the mode of action of a unique citrus thermally tolerant pectin methylesterase (TT-PME) and the nanostructural modifications it produces. The enzyme was used to produce a controlled demethylesterification series in a model homogalacturonan. Resulting demethylated galacturonides were released as oligogalacturonides with a limited endopolygalacturonase digestion, separated and quantified by HPAEC with evaporative light scattering detection. Enzyme mode of action, modeled in silico, illustrates a multiple attack mechanism, degree of processivity ~ 10, at pH 4.5 and 7.5. Average demethylesterified block size and number of blocks per molecule differ depending on demethylation pH. This enzyme’s mode of action and consequent nanostructural modifications of pectin differ from a previously characterized citrus salt independent PME.