Determination of Degree of Methylation of Food Pectins by Chromatography

Authors: Luzio, Gary; Cameron, Randall - Randy

Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/2013
Publication Date: 1/19/2013
Citation: Luzio, G.A., Cameron, R.G. 2013. Determination of Degree of Methylation of Food Pectins by Chromatography. Journal of the Science of Food and Agriculture. 93:2463-2469.

Interpretive Summary: Pectin, which is both a polyester and a polysaccharide, is a major component of citrus peel byproducts. In order to understand the functional properties of pectin being used to create new industrial materials from citrus waste it is important to verify its composition such as its ester content. The ester content of pectin has a significant for its functional properties. Measuring the ester content by traditional procedures is cumbersome and time consuming. We have devised a new approach for measuring the ester content which can be done completely using automated chromatography procedures. The chromatography procedure will enable efficient analysis when confronted with large numbers of samples for ester determinations.

Technical Abstract: After removal of soluble sugars and other compounds by washing, citrus peel is largely composed of pectin, cellulose and hemicelluloses. One of the major components, pectin can be modified using pectinesterases which reduce the degree of methylation (DM). Low DM pectins have great utility in the food industry and other applications. They have been shown to have calcium sensitivity which is an important functional property of pectins for use in applications which require suspension, metal ion binding or water absorption. Thus, an estimate of DM is an important to determine but most DM analyses are difficult to perform. A method has been developed for determination of pectin DM using hydroxide and Pectinex digest in sequence followed by analysis with ion exclusion chromatography to obtain methanol concentrations and anion exchange chromatography to obtain GA concentrations. IEC alone can be used to determine both GA and methanol in a single chromatography run but GA data may be unreliable due to possible interference from neutral sugars. Presence compounds typically found in pectins of acetate, ethanol and isopropyl alcohol do not appear to interfere with assay of GA and methanol by IEC and being volatile do not interfere with GA assay by ELSD – AEC. Colorimetric assay of GA is more difficult to perform and has been shown to be prone to errors when neutral sugars and alcohols are present which can interfere with color development. The chromatography procedure described in this report provides a facile method for determination of DM and will enable efficient analysis when confronted with large numbers of samples for DM determinations.