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United States Department of Agriculture

Agricultural Research Service

Research Project: BIOACTIVE CONSTITUENTS AND SPECIALTY FOOD FIBERS AS VALUE-ADDED PRODUCTS FROM CITRUS PROCESSING WASTE

Location: Citrus and Other Subtropical Products Research

Title: Nanostructural Characterization of Modified Homogalacturonan with Pectin Methylesterase from Jelly Fig (Ficus awkeotsang Makino) Achenes and Modeling of Enzyme Mode of Action

Authors
item Kim, Yang -
item Cameron, Randall
item Tzen, Jason T.C. -
item Williams, Martin A.K. -

Submitted to: National Meeting of Institute of Food Technologists/Food Expo
Publication Type: Abstract Only
Publication Acceptance Date: March 27, 2012
Publication Date: N/A

Technical Abstract: 1. Justification: Pectin is a major hydrocolloid used in various food, cosmetics, and medicine pharmaceutical products. The relative amount of unmethylesterified galacturonic acid (GalA)residues and their distribution are key determinants of pectin functionality. Pectin methylesterase (PME) modifies unmethylated GalA block sizes and distribution, and has potentials to develop a technology to introduce ordered demethylated block nanostructure into pectin. 2. Objective: The objectives of this study were to characterize demethylesterified block nano-structure of modified homogalacturonan and to model enzyme mode of action of a PME from jelly fig that is stable in a wide range of pH and temperature. 3. Methods: An acidic PME isolated from jelly fig (Ficus awkeotasang Makino) achenes was introduced used to modify a model homogalacturonan (molecular weight = 25,570) at 30 ºC. A controlled demethylesterification series was produced at pH4.5 and pH7.5, respectively. Demethylesterified blocks were released as oligomers by limited endopolygalactronase digestion, separated and quantified by high performance anion exchange chromatography and subjected to mathematical modeling. 4. Results: The average demethylesterified block size (BS) and number of blocks per molecule (BN) differed depending on the DM and pH (P<0.05). Significant increase in BS and BN were observed in demethylesterified homogalacturonans with 30 DM at both pHs. Homogalacturonans with 30DM and 50DM demethylated at pH 4.5 showed significantly longer oligomer blocks compared to homogalacturonans produced at pH7.5, respectively. Enzyme mode of action, modeled in silico, suggested a multiple attack mechanism and non-processive mode of action, which is comparable to processive mode of basic plant pectin methylesterases. 5. Significance of the research to the food science field. The results suggested possibility to control DEMB size and to produce a uniform population of demethylated pectin molecules, particularly in acidic environment where most basic plant PMEs are inactivated.

Last Modified: 10/21/2014