Title: CHARACTERIZATION OF ESTERIFIED BLOCKS IN PECTIN HOMOGALACTURONAN REGIONS AFTER DE-ESTERIFICATION WITH THE THERMALLY TOLERANT PECTIN METHYLESTERASE FROM CITRUS FRUIT Authors
Submitted to: Proceedings of Florida State Horticultural Society
Publication Type: Proceedings
Publication Acceptance Date: December 27, 2004
Publication Date: December 31, 2004
Repository URL: http://www.ars.usda.gov/sp2UserFiles/Place/66210000/Reprint934.pdf
Citation: Cameron, R.G., Luzio, G.A., Grohmann, K. 2004. Characterization of esterified blocks in pectin homogalacturonan regions after de-esterification with the thermally tolerant pectin methylesterase from citrus fruit. Proceedings of Florida State Horticultural Society. 117:410-415. Interpretive Summary: Pectin, a major component of citrus fruit peel, is used in the food industry as a gelling and stabilizing agent. Potential industrial uses for pectin, modified pectin or pectin containing bio-based products includes additives for a variety of manufactured products, ion exchange resins, flavor or aroma encapsulators and as coatings. The functional properties of pectin depend on its chemical structure. Small changes in its structural properties can produce very different functional properties. One method of changing its structural properties is by enzymatic demethylation. In this report we used a monocomponent prepartion of a thermally tolerant pectin methylesterase that we prepared from citrus fruit peel to demethylate pectin and probed the resulting structural changes with enzymatic and chemical methods.
Technical Abstract: A non-calcium sensitive pectin, with a degree of esterification (DE) of 73%, was demethylated at pH 7.5 with a monocomponent preparation of a thermally tolerant pectin methylesterase (TT-PME) isolated form citrus fruit tissue. The DE of the parent pectin was lowered to 66.5% and 59%. Endo-polygalacturonase (EPG) was used to digest the pectin and estimate the maximum length of methyl-protected blocks in the homogalacturonan (HG). Following enzymatic demethylation and EPG digestion the pectin was exhaustively demethylated with 0.1 M LiOH to estimate the size of methyl-protected blocks within the HG. Methyl-protected block size was estimated by high performance anion exchange chromatography coupled to an evaporative light scattering detector. At a DE of 66.5% large peaks representing oligomers of 4-16 galacturonic acid (GA) residues were present. The largest EPG protected block for the 66.5% DE pectin was a 19-mer. Surprisingly, a much larger oligomer (DP 44) was observed in the overnight EPG digested, alkaline demethylated sample. This suggests that the TT-PME may have switched to a random mode of attack or the EPG did not require four adjacent demethylated GAs for cleavage.