Characterization of Nanostructural Modifications Introduced into a Model Pectic Homogalacturonan by Esterases or Chemical Saponification and Modeling of Enzyme Mode of Action

Pectin functionality is largely dependent on the ratio of methylesterified/demethylesterified galacturonic acid (GalA) residues present in its polymeric homogalacturonan region (40 - 60 nm in length, 100 - 150 GalA residues) and how the two types of GalAs are spatially distributed within that linear backbone. These distributions translate into an ordered vs. random distribution of ionic (demethylesterified) and neutral (methylesterified) regions. Enzymatic modification of pectin nanostructure by pectin methylesterase (PME) is the only known method to introduce ionic blocks into pectin having a relatively high degree of methylesterification (> 20%). We have been characterizing the statistical parameters of average demethylesterified block size (1 - 4 nm) and number of demethylesterified blocks per molecule (0.1- 2.0) following enzymatic or base demethylation of a model 94% DM homogalacturonan by excising demethylated blocks using limited endo polygalacturonase digestion. Additionally, for enzymatic demethylation we have modeled enzyme mode of action. We will report on results obtained by demethylation with several pectin methylesterase isozymes as well as by random acting fungal PME and chemical saponification. Additionally we will present results for rheological properties related to nanostructural modifications.