ARS | Publication request: Mapping structural and functional changes in esterase-treated pectin and characterizing enzyme mode of action

Submitted to: Subtropical Technology Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: October 16, 2010
Publication Date: N/A

Technical Abstract: We hypothesized that pectin nanostructure can be enzymatically engineered with pectin methylesterase (PME) to tailor functionalities with improved consumer properties not available via conventional formulation or processing. Organoleptic qualities of processed and formulated foods are primary determinates of consumer acceptability. Stabilization of milk proteins in acid dairy drinks, gelation in jams and jellies and texture firming ionic interactions in fruits and vegetables are examples of product quality mediated by pectin molecule nanostructure. PME hydrolyzes galacturonic acid C6 methyl-esters in discrete patterns along the pectin homogalacturonan (HG) polymer. The experimental approach is to: 1) purify and characterize PME from an industrial enzyme preparation obtained from papaya (Carica papaya), 2) use PME to prepare pectin demethylation series from a model HG substrate, 3) characterize the introduced nanostructural modifications, 4) model the enzyme’s mode of action and degree of processivity, and 5) determine rheological properties of the modified HG and correlate them to the introduced nanostructural modifications. We have determined basic separation parameters for purification of PME present in the papaya extract. A single PME was isolated. Structural characterization of the purified PME by MALDI-TOF mass spectrometry will be presented as well as select biochemical properties (pH optimum, ion activation, etc.). Two demethylation series (pH 4.5 and 7.5) have been produced using a highly methylated model HG. The introduced nanostructural modifications have been characterized by HPAEC to estimate the average demethylated block size, number of demethylated blocks per molecule and enzyme degree of processivity. This data is being correlated to rheological and calcium sensitivity properties of the modified pectins for the construction of predictive models for producing pectin-based formulating agents having optimum and predictable physical properties.